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Planet Earth/6b. Plate Tectonics: You are a Crazy Man, Alfred Wegener

Alfred Wegener and Plate Tectonics
It was a great surprise when Alfred Wegener appeared at the mid-ice station in the center of the vast snowy landscape in the frozen heart of Greenland. His dog sled pulled through the Arctic cold near the onset of winter on October 19, 1930, carrying supplies that would allow the 3-person crew to remain through the winter at the weather station. Their mission had been to record the year-round weather on the great ice sheet, but supplies had dwindled during the summer, and the arrival of fresh supplies was delayed until late fall. They were going to have to abandon the weather station, but the arrival of Alfred Wegener and his younger assistant Rasmus Villumsen, changed their plans. The two travelers suffered through the bitter cold, which reached lows of −60 °C (−76 °F) to arrive at the weather station, and they were only protected by thick furs and parkas. Rasmus had lost his toes to frost bite on the journey, and they looked to the 3-person crew at the station, as if on death’s solemn door. They had only brought enough food and fuel to feed and keep warm the 3-person crew, with the hopes of returning back to their main camp. But the weather had become colder and colder, as winter was setting in. Originally, they had carried more supplies, but at the risk of losing men, only Wegener, and his assistant pushed onward with the bare minimum of supplies to staff the 3-person weather station for the winter. If Wegener refused to make the journey, there would not be enough food for the crew stationed at the isolated outpost on the ice sheet and they would starve, so he and Rasmus Villumsen drove their dog sled onward across the ice and snow into the center of Greenland. After arriving at the station and emptying their supplies for the grateful crew, the two solemn men disappeared across the ice cover world.

Fifteen years before, a much younger Alfred Wegener taught physics, meteorology and applied astronomy at the University of Marburg in Germany, a small town dominated by the Marburger Schloss, an 11th century castle on the hill top above the college. It was an ideal place to teach, and Wegener was a well-respected professor during the peaceful years before World War I. His research for the past decade was focused on the temperature of the atmosphere, and with his brother’s help, he had been sending weather balloons high into the air to record air temperatures at different levels in the atmosphere. While the Wright Brothers were attempting to develop flying machines in the United States, Wegener was launching the first weather balloons, equipped with thermometers to measure the changes in temperature with elevation. His research was published in a well-received book, Thermodynamik der Atmosphäre (Thermodynamics of the Atmosphere), which also reported on his measurements of the atmospheric temperatures at different altitudes during a brief expedition to Greenland in 1906. The trip introduced him to arctic exploration, a fascination with which he would never lose interest in. During all this research on global atmospheric circulation Wegener would stare at geographic maps of the entire Earth, and notice the odd way that the continents seemed to fit together. The eastern coast of South America appears to mirror the western coast of Africa, while North America and Europe seem to fit against each other with Greenland between them. If you could cut out the oceans, the continents appeared like a jig-saw puzzle, locking together to form a single super continent.

In 1912, Wegener submitted his crazy and wild idea at a geology conference at the famous Senckenberg Museum in Frankfurt, home to a recently installed giant Diploducus dinosaur from the United States. His lecture argued that the continents had drifted apart and their split had given rise to the ocean basins. One of his strongest and most vocal critics was a geologist named Max Semper, who studied fossil shells to understand the history of ocean currents, his research strongly suggested that the continents did not move, and the distribution of fossils implied that sea level rose and fell through Earth’s long history, but the continents stayed fixed. However, to many other geologists in the audience Wegener’s idea was an interesting one, a hypothesis that needed much testing and evidence gathering to prove whether the continents had indeed drifted apart. Wegener returned to Greenland the next year, where he crossed the Greenland ice sheet between the Denmark Havn and Kangersuatsiaq, a distance much longer than the Norwegian explorer Fridtjof Nansen had done during his crossing of Greenland. Although the expedition garnished him some fame for the young scientist, he nearly died during the trip. On his return home, he married the daughter of the famous Russian geographer and climate scientist Wladimir Köppen, who was also his own mentor and teacher. In 1913 to 1915, Wegener did not give up on his hypothesis of drifting continents and continued to write about his ideas of an ancient super continent (Pangaea) and how it broke up over time. In 1914, World War I brought him to the front, as he served in the war effort, and despite the war, he remained dedicated to formulating his ideas. During the war he published a comprehensive book of his ideas, entitled Die Entstehung der Kontinente und Ozeane (The Origin of the Continents and Oceans). Wegener immersed himself into the study of isostasis theory; that is the study of the brittle strong lithosphere resting on a ductile weak asthenosphere, and how those layers may play a role in the motion of continents over longer periods of geologic time, as plates of lithosphere carried by the motion in the asthenosphere below. He wrote, as translated into English, “one can assume that the continental crust is capable of isostatic compensation in movement, not only in the vertical direction (as in the rise and fall of mountains), but also in the horizontal direction (with the movement of continents).” Wegener took his ideas beyond just a hunch or idea, to a formally argued scientific hypothesis, filled with numerous examples of how it could be further tested. But World War I would continue to rage across Europe for another three more years. His book and ideas were not widely read, and published only in German, so they did not make it to England or the Americas. At the end of the war, Wegener did not give up on his ideas, but moved onto new scientific interests including working with the now freed Serbian scientist Milutin Milanković on Earth’s past ice ages and Earth’s oscillating orbit. In 1926, he traveled to the United States to present a lecture on his ideas in New York City, and although by now he had expanded out his ideas more fully into a theory of plate tectonics, that is the motion of thick plates of the lithosphere forming the continents and how they floated across a weak asthenosphere. His ideas were still considered radical, even among American geologists, and were not well received. He returned to Germany where he was awarded funding by the government to return to Greenland to further his climate research, and to establish a weather station in the very center of Greenland’s ice sheet. He would be put in charge of the entire expedition to capture temperatures through the 1930-1931 winter from the center of the ice sheet.

Departing from the weather station located in the heart of Greenland, the two men pushed onward over the frozen landscape. They had saved the expedition from disaster, the crew would record the temperatures through the coming winter, but they had put themselves at great risk in crossing the ice sheet this late in the year. Winter was closing inward on them. With dog sleds and the bare minimum of food and supplies for themselves they pushed onward back to the main base camp. Wegener was fifty years old, and had loved his tobacco pipe smoke. He was not ready for the excursion that came when the last of the dogs perished in the cold, and he had to drag the sled himself. Half way across the ice sheet, in the frozen landscape of Earth’s vast ice sheets, he died. Rasmus Villumsen hastily buried him in the ice, and pressed onward, never to be seen again. With Alfred Wegener’s death, the most prominent promoter for the idea of plate tectonics was gone. The idea was shelved by geologists for several decades. It would take a new generation of scientists to unearth the evidence for the motion of the lithosphere, and advance the idea of plate tectonics.

The Geology of the Ocean Floor
One of the great limitations toward the pursuit for the scientific gathering of evidence to test the idea of plate tectonics stemmed from the poor understanding of the actual geology of the ocean floor. The ocean floor is hidden under the dark deep ocean waters, and while out of view, offers the most important source of information about the motion of continents. The ocean floor under the theory of plate tectonics is young thin crust, generated by the cooling of molten magma that rises up, splitting the ocean floor wider and pushing the continents apart. The advent of World War II established to the public a widespread lack of awareness of the topography of the ocean floor. The United States Government and U.S. Navy rushed to fund programs to map the ocean floor. World War II was fought as much at sea, as it was on land. Knowledge of the ocean floor, would be useful in the search of enemy submarines lurking in deep ocean waters off the coasts. New underwater surveys were carried out using echo sounders that transmitted sound waves to the ocean bottom and record the length of time they took to be retrieved by the ship floating above. The seafloor depth could be mapped by the passage of these ships, this is known as bathymetry; the measurement of water depth. The other advanced tool developed during World War II was magnetometers that could be dragged behind a ship to record magnetic anomalies along the sea floor. Submarines are made mostly with iron, so their presence in the ocean below would cause the Earth’s magnetic field to distort, like a compass brought close to a hulk of iron. Magnetic anomalies could signal a submarine below the ship. During and after World War II ended these two technologies were used to begin the comprehensive mapping of the Earth’s ocean floor—most of this task was undertaken by a single woman named Marie Tharp.

Marie Tharp arrived in New York in 1947. She was hired to draft maps based on a new project to map the world’s ocean floor at the Lamont Geological Laboratory at Columbia University. Tharp was well educated in geology and mathematics. During the war years, there was need of women scientists to study geology in pursuit of petroleum to fuel the war, and she was recruited to study geology at the University of Michigan, graduating with a master’s degree, and went on to study mathematics in Oklahoma. Arriving at the laboratory, Marie Tharp was teamed up with a geologist named Bruce Heezen, on a project to find ships and aircraft lost during the war years. As the sole woman on the team, Marie Tharp was unable to travel on any of the naval ships, which meant that she had to stay behind to work at her drafting table, while Bruce Heezen traveled the world recording information about the sea floor. Despite the lack of first-hand experience, Marie Tharp would use the data gathered by other members of the team to map the ocean floor. It was a historic opportunity for her to fill in the last blank unmapped region of the Earth’s surface, a place never explored before. Compiling huge sets of data that recorded each ship’s geographic location and bathymetry was tedious work. But by the 1950s, she revealed a mid-ocean ridge that ran down the central axis of the Atlantic Ocean.

A ridge that rose from the ocean floor, jagged cracked and shifted along canyons representing smaller perpendicular ridges and valleys. Seismic surveys revealed that the Moho discontinuity was extremely shallow under these mid-ocean ridges, the crust thin and elevated from the ocean floor. It was further confirmed by Bouguer gravity anomalies over these mid-ocean ridges which showed a drop indicating high topography beneath the ocean, and less dense and warmer rock layers composing these ridges. These mid-ocean ridges were like cracks on egg shell splitting the oceans into two halves. Survey of magnetic anomalies of the northeastern pacific coast, revealed a zebra pattern of magnetic reversals that baffled geologists at the time. But to Marie Tharp all this evidence she had revealed and gathered from her maps of the ocean floor supported Wegener’s theory of plate tectonics—that the ocean floor was growing and expanding from these mid-ocean ridges, pushing the continents further apart. They arose up from the ocean floor, driven by thermal convection in the underlying asthenosphere. Here the mid-ocean ridges mark the spreading of the ocean floor, as molten magma is brought to the sea floor as long series of underwater volcanoes and volcanic vents. These mid-ocean ridges were the divergent plate boundaries that pushed the ocean basin’s wider. Their higher topography was a result of hot magma moving upward, and as the crust diverged from the high ridge, cooled and sank down into the deep abyssal plains. The perpendicular ridges and canyons were a result of the different rates and speed of this spreading ridges on the ocean floor, resulting in transverse faults. The magnetic anomalies in the sea floor of the Pacific Ocean appeared as bands of reverse polarities in the orientation of the magnetic fields of the iron-rich rocks on the ocean floor, they would later be found across nearly the entire ocean floor. Ribbons that appeared to record a history of growth and movement away from these spreading ridges.

The Paleomagnetist
Allan Cox was not very good in school, and struggled in his chosen program of study, chemistry. After his first semester he failed out of the University of California, and joined the United States Merchant Marines. As a sailor he traveled the oceans, and became an avid reader while at sea, he wanted to return to school and learn more about the Earth. In 1950 he was hired by a geologist Clyde Wahrhaftig to help him map and study the glaciers of Alaska. The two men embarked on the work in the Alaska wilderness. Over the course of their close working relationship, the two men fell in love. Both Allan Cox and Clyde Wahrhaftig were closeted homosexuals, a secret they kept closely guarded. Clyde Wahrhaftig pushed Cox to return to school. Cox returned to the University of California to finish his degree in chemistry, but again failed, and was drafted into the army. In the army, Cox kept up his correspondence with Clyde Wahrhaftig, and after 2 years switched his major to geology, and spent more summers in Alaska with Clyde Wahrhaftig. In 1955, Cox realized that the geology faculty were not teaching him the full story, Alfred Wegener’s writings on continental drift were forbidden text, and only one professor, Dr. John Verhoogen even acknowledged its existence in the lecture halls of the school. Cox with fellow students formed a geology cub, to meet at a local pub and drink beer and discuss the forbidden field of geology; continental drift and plate tectonics.

As a magma or lava cools and solidifies, the magnetic iron minerals it contains become magnetized parallel with the Earth’s magnetic field. The orientation of a rock’s magnetism is fixed at the time of this cooling. Earth’s magnetic field has changed over time, with complete reversals in the past where the magnetic pole becomes the south pole and vice versa. These polarity reversals preserved in the once molten rock became the basis of Cox’s research as he believed they might offer a way to test the theory of continental drift and plate tectonics. In 1959 he graduated with a PhD in geology and was hired by the United States Geological Survey to work with a team to develop a geomagnetic polarity time scale. Dating of sedimentary rock layers using magnetostratigraphy was not yet possible because, while it was known that the polarity of Earth’s magnetic field reversed over the course of its history, as the inner and outer core rotated inside the Earth, the nature of this record of polarity reversals was not chronologically understood. Allan Cox teamed up with Richard Doell and Brent Dalrymple. The research required measuring magnetic reversals in the once molten rock layers as well as calculating the radiometric age of each layer to make a workable geomagnetic polarity time scale. Their work proved very influential in the dating of rock layers for the United States Geological Survey, and became known as the Cox-Doell-Dalrymple calendar.

The observed magnetic anomalies along the sea floor of the Pacific Ocean which appeared as zebra strips where held up to the pattern revealed by the Cox-Doell-Dalrymple calendar, like two matching bar codes, the record across the mid-ocean ridge exhibited on the sea floor matched the same carefully worked out chronological pattern in rock layers elsewhere. In 1973, the theory of plate tectonics became the standard model in geology with the publication of Allan Cox’s Plate Tectonics and Geomagnetic Reversals and Marie Tharp’s 1973 map of the entire ocean floor showing the distribution of mid-ocean ridges. Textbooks were changed and both became celebrated scientists for gathering the evidence for a radical theory first formulated by Alfred Wegener.


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English-Hanzi/Ningxia

Ningxia is an autonomous region in the northwest of China.

宁夏是中国西北部的一个自治区.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: English-Hanzi/Ningxia


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Eric 6 User's Guide/Getting Started

Eric is a wonderful tool to work with if what you're looking for is full-featured, comprehensive Integrated Development Environment (IDE) for developing Python applications.

This guide (and Eric) assumes that you have working installation of Python 3 and some experience using it. If you have limited or no experience with Python, head on over to the Python web site. It contains a tutorial, extensive documentation, instructions on installation and much more. Review the options for installing Python on your OS (Linux, MacOS, Windows). Take some time to get comfortable programming in Python with IDLE, Python’s built-in Integrated Development and Learning Environment.

There are innumerable Python resources on the web, including several WikiBooks.

If you plan to develop applications with a Graphical User Interface (GUI), some experience with event-driven, object-oriented GUI design software would be at least extremely helpful.

title: Eric 6 User's Guide/Getting Started


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Talk:Eric 6 User's Guide/Getting Started

Navigation to be added


text: User:PratNil

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Free Knowledge Culture Calendar/January 4

Following an agreement between Unisys and CompuServe to collect LZW patent fees from authors of GIF-supporting software, today in 1995 Thomas Boutell published a first draft of a Portable Bitmap Format (aka PNG), a better, smaller, more extensible replacement that made GIF largely obsolete.


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Free Knowledge Culture Calendar/February 14

Today in 1989 the .ZIP file format was released into the public domain. After a lawsuit against Phil Katz as a third party developer of an (improved) implementation of the then predominant ARC format, his better and free ZIP format supplanted ARC and sealed the end of the plaintiff company SEA.


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Free Knowledge Culture Calendar/April 12

Today in 2016 Let's Encrypt completed its test phase and was officially launched.


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Free Knowledge Culture Calendar/July 1

Today in 1970 the Xerox Palo Alto Research Center was opened. From here Apple and Microsoft stole the interface concepts that made modern personal computers accessible to masses of people: the computer mouse, graphical user interfaces with windows and icons, WYSIWYG editing, ...

title: Free Knowledge Culture Calendar/July 1


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Free Knowledge Culture Calendar/November 29

Today in 1974 was the announcement of the first commercially successful personal computer, the Altair 8800, which started the microcomputer revolution.


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Free Knowledge Culture Calendar/February 18

Today in 2000 Geekcorps was incorporated.


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Free Knowledge Culture Calendar/June 3

Today in 2004, revision 1 of x264 was released, an early and fast open source encoder implementation with uncompromising quality that contributed to the enormous success of the H.264/MPEG-4 AVC video format, which in turn is a commercial, patent-encumbered standard.

title: Free Knowledge Culture Calendar/June 3


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Free Knowledge Culture Calendar/May 8

Today in 2007 Sun finished the release of all parts of Java's core code they hold the copyright for. This eliminated “The Java Trap” and made Sun the biggest Free Software contributor.

title: Free Knowledge Culture Calendar/May 8


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Free Knowledge Culture Calendar/March 19

Today in 2007 the Free Software Foundation published the GNU Affero General Public License (AGPL).


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Free Knowledge Culture Calendar/May 1

Today in 2002 OpenOffice.org 1 was released.

title: Free Knowledge Culture Calendar/May 1


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Free Knowledge Culture Calendar/September 18

Today in 1992 the first JPEG standard was published. It allows perceptually nearly indistinguishable reproductions of natural images at a fraction of the uncompressed size of the original, while the degree of compression can also be increased until the image impression falls apart. This well-engineered open standard is ancestor to almost all following popular lossy (moving) image compression algorithms, having all their main building blocks already in place. For still images, it proved difficult to improve on. It is an example of particularly long-lived, so-called “golden formats” that are especially well suited for long-term archival. While the standard specifies additional features, only those not encumbered by patents got widely implemented. Nevertheless, even the patent status of the core technology had to be defended in court.


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Planet Earth/6c. Earth’s Volcanoes: When Earth Goes Boom!

Subduction
As points of lithospheric spreading, mid-ocean ridges are the divergent boundaries where new crust is formed. Over long geological intervals, this new crust on the ocean floor pushes continents apart. If new crust is formed from these mid-ocean ridges, there must be other places where crust is equally destroyed or recycled into the interior of the Earth. Although, some crazy theories early in the 1900s proposed that the Earth expanded over time, ever growing bigger, maps of the occurrence of earthquakes and volcanoes revealed other places where Earth’s crust appeared to be destroyed by a process of what is called Subduction. Subduction is the downward movement of a lithosphere plate into the deeper molten asthenosphere, and this downward motion of the lithosphere plate is a result the collision of one lithospheric plate overriding another downwelling lithosphere plate. Subduction was first discovered by two scientists on opposite sides of the Pacific Ocean closely listening to the music that comes from deep within the Earth. A piano produces sound by hammers that strike long strings of various length. Each string produces a sound at a specific frequency, which sends vibrations through the gas particles at a matching frequency. These sound waves are heard in the ear, as the particles of gas ripple with the waves of motion that vibrate the ear drum. Geologist Hugo Benioff would listen to the Earth in the same way as he did to music: listening to vibrations coming from the Earth’s deep, and mapping these in three dimensions. Sound waves change with distance, losing energy as they travel. Low frequency sound waves travel farther than high frequency sound waves, and by listening to the Earth, Benioff could map the places that sounds originated from deep in the interior of the Earth. In certain zones, the origin of these sounds is very deep inside Earth extending down below the surface to depths of nearly 670 kilometers. Benioff pin-pointed one of these regions of deep Earthquake producing sounds north of New Zealand below the Islands of Tonga in the South Pacific in the 1940s. Independently, a Japanese researcher named Kiyoo Wadati was also listening to Earth producing sounds, and who also discovered regions of super deep Earthquakes in the Pacific, this time near his home in Japan. Today these regions are known as Wadati–Benioff zones, and they mark areas where the crust is destroyed by the downward movement of one layer of lithosphere sinking below another layer of lithosphere. As these two gigantic layers of brittle rock rub against each other, vibrations from these deep Earthquakes, radiate from these Wadati–Benioff zones in the subsurface. Mapping the depth of Earthquakes marks the boundary between the two plates of lithospheric crust as one layer is subducted or pushed below the other. Such areas exhibit the most dangerous earthquakes and explosive volcanoes. In the Pacific Ocean this ring of earthquakes and volcanoes is known as the Ring of Fire!

Subduction is the downwelling of cold brittle lithosphere below another thick layer of lithosphere. This process subjects the plunging downward lithospheric plate to extreme heat and high temperatures. The downward moving layer melts into molten magma, which is less dense and rises, forming a zone prone to both massive earthquakes and gigantic explosive volcanoes. One place this is manifested is along the northwestern coastline of North America, as a chain of large volcanoes, including the famed Mount St. Helens that tower above the Cascade Mountain Range.

Saint Helens Erupts!
On May 17, 1980, four scientists stood on the edge of camp, looking out over a view of an active volcano in the Cascade Range of Washington. The Juan de Fuca Plate is a small lithospheric plate that arises from a divergent plate boundary from a mid-ocean ridge in the ocean off the coast of the Northwest Pacific shore. The plate’s motion is east, where it plunges under the edge of the North American continent in a subduction zone. Above this region, massive volcanoes like Mount Baker, Mount Rainer, Mount Hood, and Mount Adams poke up above the clouds, with snow capped peaks. Together they form the Cascade Mountain Range. One of the most picturesque of these mountains is Mount Saint Helens, which was often referred to as the Mount Fuji of America, because of its once symmetrical shape. In 1980, the mountain was a dormant volcano that last erupted nearly 150 years before in 1842, although the last major eruption was well back in time, around 1482. The four scientists had come to see the volcano and camp on the edge of an evacuation zone. Harry Glicken was the youngest member, only 22 years old, he was an enthusiastic lover of science. Described by those who knew him as socially awkward and obsessive about volcanoes, he was skinny with thick glasses and a rough scraggly beard. He had been camping at the spot for the last two weeks, and was leaving to travel to the University of California, where he hoped to continue his education in graduate school. David Johnston had arrived at the camp to continue monitoring the volcano, in Glicken’s soon to be absence. Johnston was 30 years old, and worked for the United States Geological Survey, originally the team leader Don Swanson was going to stay at the camp, but he had a meeting with a visiting student, so Johnston made the trip up the mountain from Vancouver, to continue observations of the volcano.

David Johnston was interested in the volcanic gasses that are emitted from volcanoes, and was hoping to monitor the eruption from the distant camp, which provided a beautiful view of the volcano’s rise into the sky. The camp was joined by two young female scientists, Mindy Brugman and Carolyn Driedger who had driven up to camp nearby for the night. Mindy Brugman had designed a laser surveying tool that could measure distances. The laser surveying tool had been set up on the ridge at the camp with an unobstructed view to the volcano six miles away, and was collecting data as to the distance to the mountains edge, as it appeared to bulge upward. They had arrived to study its movement, and help if they could in data collection. They were going to camp near by Johnston’s trailer in tents.

The arrival of the scientists was a result of a series of events that started on March 15th. On that day, in 1980 a series of earthquakes were detected by seismographs that had been put into place by the United States Geological Survey (USGS) in 1972, these earthquakes indicated that the volcano might erupt soon. USGS volcanologist David Johnston had started visiting the mountain and began measuring both temperatures and collecting air samples. Helicopters carried him out to remote ledges on the volcano. From these drop off points, he quickly scaled dangerous slopes to carry out his experiments and data collection. On March 27th a plume of volcanic ash and gases erupted nearly 7,000 feet into the air, but several weeks later the eruption bizarrely ceased. The volcano appeared to return to a dormant condition. At the camp, named Coldwater II, Mindy Brugman’s laser surveying tool demonstrated that the mountain was in fact bulging upward and outward, as gas began to build in the subsurface. The laser was reflected off mirrors that had been placed on the side of the mountain by Don Swanson. Astonishingly, the mountain was growing between 5 to 8 feet higher each day, based on their remote laser measurements. That night the weather was eerily clear. Bright stars glittered in the night sky. The camp was an idyllic location to watch the mountain and observe a geological process in action. The four young scientists were all trained geologists, but young, and hence willing to risk their lives for a spectacular view of a once in a lifetime volcanic eruption. David Johnston knew more than the others of the danger they were all in. He believed that the volcanic gasses were building below the rising dome, and the lack of a recent phreatic eruption belied a ticking bomb beneath the mountain. Phreatic eruptions are explosive venting of volcanic gasses and hot steam that are ejected from a volcano during an eruption, these explosive eruptions produce large amounts of ash and pyroclastic rocks high into the sky above a volcano. They are extremely dangerous.

What makes volcanoes explosive?
Volcanos can be characterized by how much silica (SiO2) the magma contains. Both Silicon (Si) and Oxygen (O) are lithophile elements that are common in continental rocks, and within the crust and lithosphere on Earth. Silica is the same molecule that is found in glass, and like glass, solid SiO2 will shatter into tiny pieces at Earth’s surface pressure and temperature. If you have ever broken a glass or ceramic bowl, or cut yourself on a jagged piece of glass in the kitchen, you realize how brittle silica can be. Silica is enriched in the crust above subducting plates in large part because of its melting temperature, and interaction with water (H2O). As H2O and SiO2 are subducted together, the water from the overlaying ocean fills in pore spaces in the rock and is superheated with depth into steam. This steam or very hot water vapor works to lower the melting temperature of surrounding silica rock, resulting in molten liquid and magma chambers at lower temperatures than would be possible in the absence of water. The magma as it rises also melts due to the decreasing pressure, crossing the melting point as the material moves upward through the crust. Magma containing a majority of silica is called Rhyolitic magma. Rhyolitic magma is the most explosive type of magma found in volcanoes. The opposite type of magma is Basaltic magma, which contains less silica, and as such tends to be less viscous; this type of magma will often flow out of volcanoes as slow-moving lava. Lava is molten liquid magma that has come to the surface and flows out of a volcano or volcanic vent, sometimes very quickly, other times very slowly. Basaltic magma, which has low amounts of silica, tends to be less explosive but can cause significant damage as lava encounters buildings and roads, in the form of molten rock, which burns everything that it encounters; wooden houses, steel cars, and concrete buildings.

Silica can react with other elements to form a variety of minerals called silicates. These are predominately quartz in continental crust; one of the most common minerals on Earth’s surface. Volcanologists measure the amount of silica in volcanoes to determine how explosive the volcano would be. Volcanoes with rocks that contain 50% or less silica are known as Basaltic. Basaltic volcanoes are the least explosive, and include many volcanoes that erupt out of basalt-rich ocean crust. Basaltic volcanoes, like those in Hawaii, produce flowing lava. Lava is liquid molten rock at the surface, while magma is the term used for liquid molten rock buried below the surface. Both are incredibly hot, with temperatures between 800° up to 2,000° Celsius (most are between 1,000° to 1,200° Celsius). Runny smooth lava will cool to form pahoehoe. Pahoehoe is basalt rocks that form smooth undulating or ropy masses, due to low viscosity molten lava. Aa (pronounced Ah-Ah) is basalt rocks that form very rough and rugged crumbly masses, due to high viscosity molten lava.

Explosive volcanoes that contain large amounts of silica and water will produce enormous amounts of volcanic ash during eruptions. This is due to the increase in volcanic gasses that are released during an eruption in these types of volcanoes. Pyroclasts are molten rocks and magma that is ejected out of a volcano, often propelled into the air by the buildup of volcanic gasses in the subsurface. Tephra is the name of thick deposits of pyroclastic material that accumulates near volcanoes. Volcanic ash, is composed of tiny pyroclastic particles that are ejected into the sky, and because of their tiny sizes can be blown by winds great distances. The eruption of Eyjafjallajökull in 2010, and Grímsvötn in 2011 both in Iceland produced enormous amounts of volcanic ash that caused the cancellations of thousands of flights in Europe. Such enormous eruptions of volcanic ash can cause a slight global cool down, such as the major eruptions of Tambora in 1815, Krakatau in 1883, and Mount Pinatubo in 1991, all in the southeastern Pacific. These major eruptions resulted in large releases of CO2 and SO2, but the darkened sky resulted from the release of large amounts of volcanic ash, which dimmed the amount of sunlight striking Earth’s surface, temporarily cooling the planet by around 1 degree Celsius.

Types of Volcanoes
Volcanoes are any geological feature on the planet that molten material erupts from. This includes submarine volcanoes along the mid-ocean ridges of the ocean floor, as well as volcanoes that erupt on the surface of the land. Volcanoes can also be located under ice sheets in Antarctica, and result in glacier melt at depth. Volcanoes are classified based on their size and shape.

Stratovolcanoes
Stratovolcanoes are volcanoes that have steep conical mountains, composed of layers of tephra or lava, and are the classic volcano shape, with a circular crater at its summit. These volcanoes are supported by a stock of magma that moves upward, with lava that flows out from the crater, or pyroclastic material ejected from the high crater. Mount Fuji in Japan and Mount Saint Helens are examples of this type of classic volcano.

Shield Volcanoes
Shield Volcanoes are much larger broadly shaped volcanoes that form a broad dome-shape topography. They are formed by the progressive build-up of flowing lava that cools, and less by the ejection of pyroclastic materials, and as a result will often be less steeply sloped. Mauna Loa, the volcano on the Big Island of Hawaii is an example of a shield volcano.

Tephra Cones
Tephra cones or Cinder cones are smaller volcanoes that form from the ejection of large amounts of pyroclastic tephra that builds up along the volcanic vent forming a pile of material. An example of a tephra cone is the Shit Pot (sometimes referenced as the S P Volcano) located north of Flagstaff, Arizona. These tend to be rather small, and often closely associated with other larger volcanoes. These can form from fissure eruption where a vent opens up within a volcanic field.

Caldera Volcanoes
Caldera volcanoes are the largest of active volcanoes, and include enormous areas measuring many kilometers in diameter. They form a large magma chamber that is so large it is unsupported by a volcanic stock, and will sink down, with center craters forming lakes, as they fill with water. Because of their larger size, caldera volcanoes can be the most explosive and dangerous due to the extent they can reach from their centers. Eruptions are less frequent, but there are histories of such mega-eruptions in the past. An example of a caldera volcano is Yellowstone, which sits on top of this super volcano, a smaller caldera volcano is Crater Lake in Oregon.

Flood Basalt Volcanoes
Flood Basalt Volcanoes are large volcanoes that flood the surrounding landscape with lava flows that can encompass enormous regions. Evidence of flood basalt volcanoes are found in the widespread layers of basalt that form during these eruptions. The Columbia River Flood Basalts are an example of this type of volcanic eruption pattern, where thick layers of lava flowed over a large province in Oregon.

Large Igneous Provinces
Large Igneous Provinces (LIPS) are volcanic eruptions that are of a massive scale, and result in very large eruptions of lava, with magma traveling through extensive dykes and sills. Dykes are vertical magma chambers while sills are horizontal magma chambers. Large Igneous Provinces encapsulate large regions of the Earth (thousands of kilometers), and often are associated with major biological extinctions. These eruptions produced the Deccan Traps in India and Siberian Traps in Russia. The term trap is used because the terrain of basalt rocks they leave behind is very steep and complex.

Where do volcanoes form?
The majority of volcanoes are typically found in regions of subducting lithospheric plates, but not all volcanoes form along these plate boundaries. Many volcanoes, especially submarine volcanoes are found along mid-ocean ridges. Other volcanoes are found in rifting valleys, where the overlaying lithospheric plate is stretched and thinned (sometimes pulled apart and breaking into normal faults), this allows the upward motion of molten magma below these thin regions in the crust of the Earth, while other volcanoes are associated with hot spots. Hot spots are a geologically intriguing features which are believed to be caused by a shallow convection of magma deep in the asthenosphere rising upward, or even coming from deeper layers in the Earth from the rising of heat from deep in the lower mantle. This extra heat results in melting the lithospheric plate that passes above. Like a candle held under a piece of paper passing above it, the hot spot will result in scorched line of volcanoes, fading from most active to dormant to extinct, as the lithospheric plate passes over this hot spot. The Hawaii Islands are believed to be formed by a hot spot that exists in the Pacific Ocean, while Yellowstone is also believed to be a result of a hot spot passing under the interior of North America. The idea of hot spots is very contentious, as some geologists suggest that they form not from mantle plumes of magma driven by convection, but by lithospheric plates cracking or breaking apart in these regions. The plume versus plate debate over the origin of hot spots is very active in geology.

Volcanic Hazards
Volcanoes pose major hazards to those that live in close proximity to them. Cities can be consumed by fast moving pyroclastic flows, poisonous gases can kill animals and people when released from volcanic vents, tephra can result in slope failure and major landslides, sweeping villages away, and associated earthquakes can trigger a tsunami. Thousands of human lives have perished due to the volatile nature of volcanoes. Over 23,000 people were killed during an eruption of Nevado del Ruiz in Columbia in 1985, when massive volcanic mud flow (called a lahar), swept away the city of Armero. The 1982 eruption of El Chichón in Mexico covered large areas in volcanic ash and resulted in major local agricultural loss, as well as killing 4,000 people that lived near the volcano. Closely monitored seismographs are important to give warning to evacuate nearby towns and cities, when earthquakes start, volcanic eruptions quickly follow. Drainage ravines from steep volcanoes are also prone to pyroclastic flows and should be abandoned for long term habitation because of the dangers they pose to people living in these dangerous places. Since volcanoes erupt infrequently, often on scales longer than people live, memories of their destruction are short, and often people are falsely lulled into a sense of safety. David Johnston knew the danger he was placing himself that night at the camp overlooking Mount Saint Helens. He told Mindy Brugman, Carolyn Driedger and Harry Glicken that they should drive back to Vancouver. They wanted to stay for the night, but realized the concern in his voice when he told them to all leave. They drove down the mountain, as only David Johnston stayed to watch the stars and waited for the mountain to erupt. At 8:32 a.m. on May 18th 1980, the morning sun shone down on his camping trailer as David Johnston suddenly watched the gigantic mountain before him begin to collapse. The bulge on the side of the mountain fell, and volcanic ash shot laterally directly toward his ridge. The entire side of a mountain was ejected upward and outward toward him, crossing the six miles in seconds. He reached for the ham radio and shuttered his final words, “Vancouver! Vancouver! This is it!” His last moments of his life were observed by Gerry Martin, a local Radio Amateur Civil Emergency Service operator who had camped at an observation post higher up. He messaged out “Gentlemen, the camper and car that’s sitting over to the south of me is covered. It’s going to hit me, too.” He was never heard of again. The blast reworked the topography of the terrain as the entire side of the mountain collapsed and was blasted outward toward the ridge where David Johnston was camped. About 300 square miles was utterly destroyed, and 57 people died during the eruption, including both David Johnston and Gerry Martin. The three survivors, Mindy Brugman, Carolyn Driedger and Harry Glicken who had driven back to Vancouver, would all dedicate their lives to studying volcanoes, and warning the public about their dangers.

The Earth is a dynamic planet, one that is being reformed by processes that work on both fast and slow scales of time. The intense heat and pressure locked within Earth’s interior can be unleashed, and result in devastation.


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Eric 6 User's Guide/Getting Started/Overview

Eric is a full featured Python editor and integrated development environment (IDE), written in Python. It has many uses: as an everyday quick-and-dirty Python editor and debugger, as GUI development platform, as a professional project management tool and as a multi-project portfolio manager.

In its most basic form, Eric is an excellent quick-and-dirty Python editor and debugger thanks in part to the tight integration of the highly flexible Scintilla editor control. Eric exposes many of the editor’s settings, allowing the user to customize the visual environment at will.

Eric can support rapid and sophisticated GUI development, through its integration of Qt’s UI toolkit and PyQt, and is itself an excellent demonstration of the power of Python, Qt and PyQt.

Among Eric’s multitude of features are: • Flexible editor with syntax highlighting, autocompletion and call tips • Built-in checkers for Python (syntax, issues, style,...) • Built-in documentation viewer (and web browser) • Interface to Mercurial and Subversion • A highly configurable interface

For a more comprehensive point-form list, see Feature Summary.

Like Python and Qt, Eric is cross-platform, installable in Windows, Linux or MacOS.

Eric includes a plug-in system, which supports easy extension of the IDE’s functionality with downloadable plug-ins.

The current stable version is eric6 based on PyQt5, Qt5 and Python 3. Eric is distributed under the GNU General Public License, version 3 of 29 June 2007. Other components are licensed differently – see Licensing.


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Planet Earth/6d. You Can’t Fake an Earthquake: How to Read a Seismograph

An Earthquake?
Horizontal coal layers erode out of the cliffs in central Utah west of the town of Huntington. The Crandall Canyon Mine provided coal for the nearby Huntington Power station, which uses coal to generate electricity. In the early morning of August in 2007, the roof of the mine collapsed trapping six miners 1,800 feet beneath the surface inside the coal mine. Emergency responders raced to the scene to find that the mine was completely buried in the collapse. As new media arrived to the scene and attempts were made to rescue the six miners, the owner of the mine, Bob Murray, emphatically argued that the mine collapse was due to a naturally occurring Earthquake, rather than an over-weakened mine shaft that had collapsed. As rescue attempts proved fruitless, and another 3 people died in attempts to locate the trapped Utah miners, the question of whether the mine collapse was due to poor supports holding the roof, or whether the mine collapse was a result of an Earthquake became a central question. Unknown to the mine owner, one of the largest geological experiments ever conceived was being conducted that summer in Utah, as hundreds of high-quality, portable seismographs were being deployed across the United States to record the motion of the North American continent. This network of seismographs is known as the US Array. High resolution GPS stations deployed by the National Science Foundation’s Earthscope initiative recorded the actual motion of the continental plate, with partnerships with many university seismologists who added to the research through the IRIS program (Incorporated Research Institutions for Seismology). This massive government effort to measure the motion of the Earth resulted in amazing insight into the dynamic nature of the North American lithospheric plate. Measurements demonstrated the quick motion of Southern California northwest, while in Oregon and Washington the motion is toward the northeast. The Pacific lithospheric plate under Southern California slides across the San Andreas fault, at a measured rate of over 50 millimeters a year. The San Andreas fault is a transverse plate boundary that separates the Pacific plate (including the Pacific Coast of California) from the North American plate, rather than the plates diverging or subducting they are actually moving laterally against each other making the region highly prone to Earthquakes. Utah on the other hand, in the interior of the continent, does not move very quickly, with motion restricted to only a few millimeters a year. Much of this motion is in the Great Basin in Western Utah near the Nevada border. The North American plate is colliding with the Pacific Plate, and spinning slowly clockwise as it spins, but only few millimeters a year. This motion is slowly pulling apart western Utah, forming an ever-widening basin region, called the Great Basin. [See: https://www.unavco.org/software/visualization/GPS-Velocity-Viewer/GPS-Velocity-Viewer.html] However, in eastern Utah the motion is nearly 0, with no motion detect at the many GPS stations deployed to the area. The region around the Crandall Canyon Mine is not near any plate boundaries, nor active or extinct volcanoes, and is in a tectonically quiet region of North America. It seemed unlikely that an Earthquake caused the mine collapse.

Locating Earthquakes
Seismographs not only record the motion of the Earth, but they can be used to detect exactly where an Earthquake originates from. The ability to pin-point an Earthquake’s location is a vital tool to geologists. To locate an Earthquake requires a minimum of three seismographs positioned near the Earthquake. The Earthquake will produce three propagating seismic waves. P-Waves, S-Waves and Surface Waves. P-Waves are the fastest traveling waves, followed by S-Waves with Surface Waves the slowest traveling seismic wave. P-Waves will always arrive at each seismograph first, while S-Waves will be the second arriving seismic wave, followed by the Surface Waves; each recorded as squiggly lines. Both P-Waves and S-Waves are called Body Waves, since they also travel through the subsurface (the body of the rock layers). The difference between the arrival times of the P-Waves and S-Waves is known as the S-P Interval, and is proportional to the distance from the Earthquake. Think of the P and S seismic waves as runners in a race on a track. They both start at the same line. The faster runner will win the race (P-Wave), while the slower runner will come in second (S-Wave). If the faster runner outpaces the slower runner at a constant speed, the distance between the two runners will grow farther apart, the farther they are from the starting line, if they run 10 meters they will be closer together than if they run 1000 meters. The greater the distance between the arrival times of P-Waves and the S-Waves, the farther the Earthquake is located from the seismograph. Each S-P Interval will give a unique distance from the station, and using three seismograph stations circles of each of these measured distances can pinpoint the epicenter of an Earthquake. An epicenter is the location on the surface of the Earth directly above the location of the Earthquake, and is found by triangulation of three (or more) seismographs. A focus is the actual location of the Earthquake in the subsurface, underground. The epicenter and focus of the 3.9 magnitude Earthquake that morning was directly over the Crandall Canyon Mine, but that did not necessarily distinguish a mine collapse from a natural occurring Earthquake.

Earthquake Magnitude
In 1930 Beno Gutenberg left Germany, and his failing father’s soap factory for a new life in the United States, it was a good choice to leave the country when he did. In the United States Gutenberg established the California Institute of Technology Seismological Laboratory to study Earthquake activity under the active Pacific Plate in California. Although struggling with English and the new culture of Southern California, he continued his research on seismic activity. In 1936 he hired an awkward physicist named Charles Richter. Richter was a native of Los Angeles, and involved in Earthquake research. The two scientists were opposite to each other, the reserved older German Gutenberg and the young American Richter who spent his free time at nudist colonies with his long-time wife (a romance writer), and rubbing shoulders with Hollywood stars of the 1930s. The two worked closely to develop a magnitude scale. The scale was a logarithmic scale to classify the strength of Earthquakes. Looking at seismographs, the vertical squiggles (amplitude) were taller the closer the Earthquake was, but also taller the bigger the Earthquake was. This was the same issue facing astronomers who classified a star’s brightness; as it is difficult to tell if a star is bright because it is close, or because it is big. The same was true of Earthquakes, so they developed an independent way to classify an Earthquake’s magnitude independent of its distance from the recording seismograph, this became known as the Richter Scale. To determine the Richter scale, a geologist will look at all the records of seismographs recorded of an event and select the largest ground motion recorded (highest amplitude). The logarithm of the vertical height of the maximum amplitude is taken (measured in micrometers/microns). A correction is applied based on the distance between the first arrival time and the log of the maximum amplitude. This simple procedure allowed earthquakes to be quickly assessed as to their Richter magnitude. On the Richter scale, Earthquakes between 0 to 3 are rarely felt, but are recorded on seismographs. Earthquakes above 3 to 5 are felt but do not cause much damage. Earthquakes above 5 are destructive, depending on where they occur. The 1906 San Francisco Earthquake was 7.9 on the scale, while the largest ever recorded Richter scale Earthquake was the 1960 Great Chilean earthquake, which was recorded as 9.5. The 3.9 magnitude Earthquake recorded directly over the Crandall Canyon Mine was not enough to cause much damage and would have been slightly felt in the motion of Earth to a nearby observer.

Push and Pull of Earthquakes
Earthquakes are produced by the motion across a fault. A fault is a plane or surface between two moving blocks of solid rock. Faults can be oriented as either mostly up/down vertically or more horizontally depending on the stresses subjected to the solid rock. Normal faults are faults that are oriented more vertically and are caused due to extension, when the rocks are pulled apart. In a normal fault one block of rocks will drop by sliding down the fault surface. Reverse faults are also oriented vertically, but are caused due to compression, when the rocks are pushed together. One rock block will ride over the other. Reverse faults are very rare, hence most vertically oriented faults are normal faults. Horizontally oriented faults are called thrust faults, and are a more commonly a result of compressional forces applied to rock blocks. In thrust faults one block will slide over another block, often in a more horizontally oriented plane. Normal faults are common in regions that are experiencing stretching or extension, while thrust faults are common in regions that are experiencing collision or compression. A strike-slip fault is a fault that where two blocks slide next to each other without much if any vertical motion. Faulting only occurs in rock layers that are within the brittle zone of the crust, rocks below this zone will plastically deform into folds. Structural geologists study the dynamic nature of faulting and folding observed in rock layers on the Earth. Earthquakes resulting from the motion of a fault will produce either a push or pull depending on their orientation and motion. If the first motion of the P-wave is upward on a seismograph, the motion was a push away from the epicenter, while if the first motion of the P-wave is downward on a seismograph, the motion was a pull away from the epicenter. If an Earthquake moves across a typical strike-slip fault, seismographs from each quadrate will record either push or pull motions. If an Earthquake moves across a thrust fault or normal fault, half the seismographs will record a pull and half a push. Study of the push-pull record in a group of seismographs can help geologists orient the direction of motion across a fault.

In 2008 Douglas S. Dreger, Sean R. Ford and William R. Walter examined the record of seismographs recorded during the Crandall Canyon Mine disaster in Utah as part of the US Array experiment. They noticed that all the seismographs recorded a pull motion, or dilation in the first arrival of the P-waves. Such motion suggested that the mine collapsed, resulting in a pull motion on the surrounding rocks inward into the mine. This was recorded by seismographs. The mine disaster thus was concluded as being caused by the roof of the mine collapsing on the workers, and not an Earthquake.


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Planet Earth/6e. The Rock Cycle and Rock Types: Igneous, Metamorphic and Sedimentary

What are Rocks?
Rocks are any solid inorganic substance that occurs naturally. This includes nearly all the solids in Earth’s interior and surface, and is the material that is most frequently used in the construction of houses, buildings, roads, and items used in everyday life.

What are the major types of rocks?
Rocks can be divided into three major types based on their formation. Rocks can be solids that have been cooled from molten liquid magma or lava (igneous rocks). Rocks can be changed or altered by deep pressures and intense heat in the subsurface, which does not completely melt the rock (metamorphic rocks). Or rocks can be composed of smaller fragments of other rocks or organic matter that have been glued or adhered together by a process called lithification (sedimentary rocks).

The Rock Cycle
These three types of rocks form a cycle. Magma and lava cool to form igneous rocks, which are eroded at the surface to break apart and be transported, where they are buried and become sedimentary rocks, which can be further buried with increasing pressure and temperature, until they turn into metamorphic rocks, and if they continue to be heated, and melt into magma and are returned to igneous rocks when cooled. This rock cycle is a continuous process on Earth’s surface caused by the continued creation of rocks by cooling magma, erosion caused by water and wind, and the burial of rocks in subduction zones, that result in metamorphic rocks. This long history of recycling Earth’s solid rocks has resulted in a surface shaped over long spans of time into a unique configuration, when compared to the more static rocks found on other planets.

One of the key aspects of the Earth’s rock cycle is that the type of rocks found in different regions of the Earth are directly related to this long-term rock cycle of melt, cool, erode, transport, burial, change, and melt. The ocean floor of the Earth’s surface is dominated by igneous rock that have recently been formed by mid-ocean ridges. These young igneous rocks will move over time into subduction zones and be melted back down into the mantle. Above the subduction zones, magma will also be brought to the surface in volcanoes and mountains which will erode and these transported fragments will be carried into basins both on land, and on the sea floor. These sediments of rock fragments will be buried and form sedimentary rocks. These sedimentary rocks can be eroded themselves when exposed to the Earth’s surface, or undergo metamorphism with deep burial, and change. These metamorphic rocks might be brought up to the surface and eroded forming sedimentary rocks. The interchange of the three types of rocks is common on Earth. If we compare the Earth’s rock cycle to that of the dormant Moon, we see a striking difference. The Moon lacks active volcanoes, tectonic plates, and is only subjected to impact structures as a process for changing rocks on its surface. This means that the moon’s rocks have existed in their current state for billions of years, dating back to when the moon cooled down to the point that magma and lava was no longer melting rocks. Since the moon lacks oceans or an atmosphere, the rocks are not eroded or transported beyond where they have cooled and formed. The only way rocks on the moon are transported is during rare impacts of asteroids or meteors on its surface, otherwise these rocks stay in place. This permeance of the surface of the moon is one reason that the Apollo 11 astronauts’ footprints will last billions of years, while footprints on Earth will last only days. It is also why impact craters are visible, as unlike on Earth, impact structures are fairly permanent features on the Moon’s surface.

Mars is also less dynamic when it comes to its rock cycle. Although it has an atmosphere, which results in wind erosion. Sedimentary rocks are formed on Mars by transported grains by the action of these winds, and the recent discovery of sedimentary rocks by the Martian rovers from water transported grains. These rocks are evidence of a very early history of liquid water on Mars, with transported rock fragments by flowing water several billion years ago. However, the vast majority of rocks on Mars are igneous rocks and cooled from their early formation. Mars has several large volcanoes, but lacks large scale tectonic plates, indicating a cooler mantle that lacks the convection of heat as on Earth.

One of the great mysteries in geology is what makes Earth rock cycle so dynamic? This is likely due to the combined motion of tectonic plates, active volcanism, presence of liquid water on its surface and a thick atmosphere. Exploration of the surfaces of larger gas planets (Saturn, Jupiter and Neptune) or the extremely hot surface of Venus, may reveal rock cycles as dynamic as those found on Earth, but likely dynamic in very different ways.

One of the challenges that will face you when you pick up a rock is how to identify the rock as either igneous, metamorphic or sedimentary. To do this, you need to think about the processes that led to the formation of that rock. But here are some tips for identifying a rock’s type.

Igneous rocks
The best way to identify igneous rocks is that they have crystals that intergrow with each other. This is because the rock has cooled down from molten hot magma or lava, which allows crystals to grow as it cooled. The problem you may face is when the crystals are very tiny, these tiny crystals are a result when the rock cooled very quickly from magma or lava, before the crystals could grow to a large size. Often you need to look very closely at the rock with a hand lens and see if there are tiny crystals present. Crystals in igneous rocks tend to be sparkly, bright, sometimes transparent, often with a variety of colors. But often igneous rocks are mostly black or gray, with tiny crystals that are not very shiny or colorful, unless you look at them closely.

Sedimentary rocks
The best way to identify sedimentary rocks is to see if they are composed of grains or pieces of other rocks. Pieces of other rocks are called clasts. A clast, is a fragment of another rock. Grains or clasts are typically dull colored, because they have been eroded and transported by wind or water. They can be well rounded or angular in shape. These grains or clasts are glued together by cement composed of minerals that easily dissolve in water, such as calcite and silica. This glue can be shiny, and form large crystals if there are spaces or cavities in the rocks. Geodes are frequently found in sedimentary rocks resulting from a cavity or space within the rocks that was infilled with cement or glue that grew into crystals, other geodes can form inside igneous rocks resulting from cavities in magma or lava, in which large crystals grow into. Some sedimentary rocks can be sparkly, but the majority are dull colored. Not all sedimentary rocks are composed of grains or clasts (often called clastic sedimentary rocks), some sedimentary rocks can be formed from organic matter. Limestone is a unique sedimentary rock composed of fossilized shells of aquatic organisms. These organisms when they die result in the burial of calcium carbonate (CaCO₃), the material that they form shells with. This accumulation of calcium carbonate is deposited and buried on the ocean floor and lake bottoms. These sedimentary rocks are called carbonate sedimentary rocks. Some organic matter, such as wood, when buried will turn into coal, another sedimentary rock. Any organic matter buried and turned to stone is a sedimentary rock. Sedimentary rocks are the only rock type that preserves fossils, and the only type of rock in which fossil fuels (coal, petroleum, and natural gas) are found.

The last type of sedimentary rock are rocks formed from the evaporation of salt water, that leaves behind salts. These are evaporitic sedimentary rocks. These salt deposits are crumbly and typically white to gray in color. They can form unusual rock layers, due to their propensity to dissolve or flow in the presence of ground waters.

Metamorphic rocks
Metamorphic rocks have undergone intense pressure and heat to result in changes in the structure of the rock and crystals, without completely melting the rock. Metamorphic rocks typically are very shiny and will sparkle in the light, because the grains or crystals have partially melted or recrystallized with this intense pressure and heat. The one thing that characterizes metamorphic rocks is something called foliation. Foliation is sheet-like wavy planar structures in the rock caused by shearing forces or differential pressures. These resemble wavy lines, often where one mineral has formed by partial melting or recrystallization. Unlike sedimentary rocks, which can have bedding or individual layers, foliation is typically wavy. The sparkly and wavy patterns in metamorphic rocks typically make them easy to identify, although there is a gradient between sedimentary and igneous rocks and metamorphic rocks. Low grade metamorphic rocks are rocks that have not been subjected to heat and pressure may closely resemble sedimentary or igneous rocks, while rocks subjected to intense heat and pressure will be radically different. This swishy definition can be somewhat subjective. A classic type of metamorphic rock is marble, which is limestone that has undergone intense pressure through burial and heat, recrystallizing the rock, making it sparkle and adding wavy lines of color (foliation).

All rocks can be classified into one of these three types; igneous, sedimentary or metamorphic. Geologists will often specialize in the study of one of the rock types. Such as the colloquial use of the terms hard rock geologists, to refer to geologists that study only igneous and metamorphic rocks, and soft rock geologists, to refer to those that study only sedimentary rocks; ironically, despite all three rock types being equally hard. Each rock type can be divided into unique rock names, which are classified based on the mineral content of each rock. Before you can learn how to identify rock names, you will need to learn about minerals, and how you can identify those in hand samples.