- formed in two ways;
- collapse of surface rock into empty magma chamber
- explosive volcanic eruption
- Explosive caldera formation
- very large magma chambers filled with silica-rich melt and abundant gas move upwards from depth.
- very high viscosity that enables them to hold gas bubbles under very high pressures.
- As it rises to the surface the reduction of pressure causes the gases to expand.
- break-through occurs the result can be an enormous explosion which blasts away large volumes of rock to form the caldera.
- Crater Lake Oregon
- Yellowstone supervolcano
- fluid basaltic lava
- released through vents (fissures)
- low magnitude due to constant release of pressure
- Distinct bursts of fluid lava (basaltic-andesite)
- Explosions usually occur every few minutes at regular or irregular intervals
- Explosions are due to trapped gas bubbles
- Producces tephra
- Least violent of explosive eruiptions
- volcanic eruption from fracture in earths surface
- underlain by reservoirs of basaltic magma
- Mid-oceanic ridges- divergent plate boundaries
- Iceland, an extention of the Mid-Atlantic ridge
- Hawaiian shield volcanoes
- Steep-sided and cone-shaped
- Made up of layers of ash and lava
- Andesitic// Ryolitic lava
- Mount Etna Italy
- Typically hot spot locations where the crust is particually thin or weak
- Balsitic lava
- Only explosive if water gets into vents
- Gasses escape very easily
- Gently sloped & made from layers of lava
- Mauna Loa Hawaiian islands
- Formation; within stratocolcanos
- large eruptions empty out the magma chamber in the summit of the composite volcano.
- It collapses forming a depression.
- Inside the depression magma oozes out to begin forming a small lava dome.
- Formation; steep sided volcanosAndesitic/ Rhyolitic lava
- Lava domes form on the steep sides of volcanoes
- they can become dislodged during an eruption
- most dangerous type of lava domes due to exposure of molten rock that become pyroclastic flows as the gases are released
- Mt St Helens
- Mt Pelee Caribbean
Cinder Cone Volcano
- Smallest and most common volcano
- Occurs in basaltic lava fields or parasitic cones on stratovolcanoes or shield volcanoes.
- Balsitic lava released
- Tephra released if gas is trapped
- Cinder cones generated by strombolian eruptions
- Sunset crater Arizona US
- Short, violent and relatively small explosion of viscous magma
- Andesitic lava
- Produce tephra, ash clouds, and pyroclastic flows
- Largest and most violent of all eruption types
- Caused by the fragmentation of gassy very viscousmagma
- Rhyolitiic magma
- Releases enormous amounts of energy
- Produce falls of ash, scoria and lava bombs and pyroclastic
- Mt St Helens
- Mt Vesuvius
Intrusive Igneous Activity
Intrusive igneous activity- materials injected into the crust are intrusive landforms, which are exposed through erosion or overlaying rock.
Sills: Whin N- England
- parallel bedding planes
- cracks run horozantally and provide lines of weakness where magma flows
- As it cools, the magma contracts providing cracks in the rock
Dykes: Channel Islands
- Cut accross the bedding planes of rock
- Magma forms cracks and weaknesses.
- It cools and solidifies before reaching the surface forming liniar ridgs where its exposed.
- Large masses of intrsive rock
- Forms doming on surface
- Heat transfered from the magma created metamorphic rock.