Types of Volcanic Eruptions
In order to understand volcanoes it is important to understand the types of volcanic eruptions which are what in the end a volcano will mostly be known for. When people hear about an eruption the first thing that comes to mind is the explosive spew of lava which is seen in movies and even most of the documentaries but the fact is that some eruptions are very small and the amount of lava that will come out will not put anyone in danger. During an eruption other things besides lava are also expelled from the vent and that includes ash, blocks, gas and tephra. By observing the volcano’s activity prior to a possible eruption you can tell which type of eruption is possible.
The Hawaiian eruption will have fluid lava, which is sent into the air from the vent or the line of vents in jets. In these types of volcanic eruptions, the jets could last for several hours which is called a “fire fountain.” When the bits of lava fall down after being shot up they can create lava flows or in other cases they will build hills which are called spatter cones. The flows of lava may also show up at the vents even when the fountaining has stopped. If the lava is flowing fast enough it could travel several miles before it hardens after cooling down.
The reason why these types of volcanic eruptions are called Hawaiian eruptions is because of the Kilauea volcano which can be found on Hawaii’s Big Island. This volcano is famous for its amazing fire fountains. In 1969 through 1974, Mauna Ulu had Hawaiian eruptions, which produced lava fountains that shot up over 1,000 feet while the eruption was taking place.
A Strombolian eruption is a type of eruption that could be classified as low level. These types of volcanic eruptions were named after the Stromboli volcano in Sicily, which experienced this type of ejection several times. These eruptions can be small to medium when it comes to the volume with some periods of violence. A Strombolian eruption is a very distinct burst of lava that takes place at the mouth of a lava filled summit conduit. Because the lava flows during these eruptions are more viscous, they are thicker and shorter than other eruptions, such as Hawaiian ones.
However, because the eruption does not strongly affect the conduit system, these eruptions can last a long time. In fact, some volcanoes have produced continuous Strombolian eruptions for many decades. An example of a Strombolian eruption that lasted a shorter duration is the Paricutin volcano, which erupted continuously from 1943 to 1952. A longer lasting one is Mount Erebus in Antarctica which has had these eruptions for many decades and of course the namesake for this type of eruption, the Stromboli volcano in Italy has actually been producing these types of volcanic eruptions for thousands of years.
Another one of the short but violent types of volcanic eruptions is the Vulcanian eruption. These eruptions can create extremely powerful explosions that cause material to travel at speeds greater than 800 miles per hour and gain an altitude of several kilometers. In addition, Vulcanian eruptions produce ash clouds and tephra in addition to pyroclastic density currents, which is a mixture of rock, gas and hot ash that flows in a manner very similar to fluids. The tephra from these flows is generally spread out over larger areas than the tephra emitted during Strombolian eruptions. Generally, the pyroclastic rock will create a volcanic cone made of ash and the resulting ash will cover a large area surrounding the volcano.
These eruptions are caused by either a lava dome rupturing or when a plug of the lava from a volcanic conduit fragments and explodes. In addition to lasting anywhere from days to months or even years, these Vulcanian eruptions may also be a precursor to larger and more explosive eruptions. These types of volcanic eruptions are named after the small volcano found on Vulcano, an island in Italy.
The most spectacular and most violent of all types of volcanic eruptions is what is known as a Plinian eruption. This type of eruption happens when gassy magma is fragmented and associated with very viscous magma. The combination releases a huge amount of energy, which will create an eruption column which will contain ash, gas and could rise up to an altitude of 50 kilometers at very high speeds. Because the ash goes up so high, it could end up several thousand miles away from the volcano’s location. This type of eruption has been compared to a nuclear explosion because of the mushroom shaped eruption column it will create.
These types of volcanic eruptions are named after Pliny the Younger who was a Roman historian that made the comparison back in 79 A.D. when Mount Vesuvius erupted so Plinian eruptions were named after him. These types of eruptions do happen and the one that took place at Mount St. Helens in 1980 is one of the best examples. They are extremely dangerous and destructive and could destroy the entire top of the mountain. Ash and lava bombs can land several miles away from the volcano and the currents of lava will destroy anything in the surrounding area. Because of the amount of material released during an eruption it is possible that the mountain will go into a resting period right after the eruption.
The Surtseyan eruption is a hydromagmatic eruption. The lava or magma will interact with water in an explosive manner. Most of these eruptions will take place underwater when a volcano becomes too large, enough to break to the surface. When the water expands and turns into steam, any water that touches the hot lava will explode creating plumes of ash, scoria and steam.
In 1963, a Surtseyan eruption took place in Surtsey and that is where the name comes from. This eruption eventually switched from a Surtseyan to a Hawaiian type of eruption. In more recent times in 2009 near Tonga the volcanic island of Hunga Ha’apai started to erupt. The steam and ash rose over 5 miles in altitude.
How The Eruption Type Is Determined
There are several things that will help determine the types of volcanic eruptions. The first thing that you will be looking at is the gas and crystal content as well as the temperature of magma. Magma which contains a lot of crystal will be more likely to produce an explosion rather than a flow so some scientists are able to examine that before an eruption takes place. Another thing that influences the type of eruption that you will see is the gases in the volcano. When the gas cannot escape from the magma then it could cause an explosion but if it can be released without any explosion or maybe a few minor ones, the eruption may be a little milder.