Video on Youtube: Volcano Eruption – The Eruption of Mount St Helens minutes

VOLCANOES

Lithosphere Side vent Pipe Central vent Lava flows Dike Sill Magma chamber Magma chamber Magma, which originates in the asthenosphere......rises through the lithosphere to form a crustal magma chamber. Lavas erupt through a central vent and side vents,......accumulating on the surface to form a volcano.

Magma reservoir Lava flow Flank eruption Central vent 10 km 60 km Shield volcanoes are built up by the accumulation of thin basaltic flows. Most commonly found in Hawaii – Mafic lava flows out and runs parallel to oceans (not the triangle type of some other volcanoes)

Mauna Loa (Hawaii) Mauna Loa (Hawaii)

Crater Lava dome Volcanic domes are bulbous masses of felsic lava, which are so viscous that they pile up over the vent. Similar to Mt St Helens – The lava is so viscous that they end up piling up and then later blow all in one time.

Mount St. Helens (Washington) Mount St. Helens (Washington)

Central vent filled with rock fragments Cinder-cone volcanoes are made of layers of ejected material that dip away from the crater at the summit. The vent is filled with fragmental debris. Successive layers of ejected material

Cerro Negro (Nicaragua) Cerro Negro (Nicaragua)

Central vent filled from previous eruption Stratovolcanoes are built from alternating layers of pyroclastic material and lava flows. Riblike dikes strengthen the cone. Pyroclastic layers Lava flows Radiating dikes Alternating layers of pyroclastic and lava

Mount Fuji (Japan) Mount Fuji (Japan)

Craters are found at the summits of most volcanoes. Mt. Etna (Sicily, Italy) Mt. Etna (Sicily, Italy)

Calderas result when a violent eruption empties a magma chamber, which collapses, leaving a large, steep-walled basin. Crater Lake (Oregon) Mount Mazama created Crater Lake in Oregon

Mt. Mazama STAGE 1 Fresh magma triggers an eruption of lava and ash.

STAGE 2 Eruption continues, and the magma chamber becomes partly depleted.

STAGE 3 The mountain summit collapses into the empty chamber.

STAGE 4 A lake forms in the caldera. Crater Lake

Lava Cinder cones Cinder cones Earlier flows Fissures Highly fluid basalt erupting from fissures… …forms widespread layers rather than mountains.

Continental crust Continental crust Continental mantle lithosphere Continental mantle lithosphere Continental volcanic belt Active volcano over hot spot Active volcano over hot spot Mid-ocean ridge Island arc Ocean plate Ocean plate Mantle plume Mantle plume Rising magma Rising magma Hot spot Hot spot Extinct volcano At ocean-ocean convergent boundaries, magmas give rise to volcanic island arcs erupting basaltic and andesitic lavas. Magmas formed at ocean-continent convergences give rise to volcanoes erupting andesitic lavas. Plate separation at a mid-ocean ridge results in basaltic volcanism. Plate motion over hot spots creates midplate chain of basaltic volcanic islands.

Direction of plate movement Older extinct volcanoes Hot-spot volcano Asthenosphere Lithosphere Hot-spot ASIA NORTH AMERICA PACIFIC OCEAN Equator Emperor Seamounts Midway Hawaii Tahiti Galápagos Islands 64.7 Ma Midway 27.7 Direction of plate movement Nihau 5.5 Kilauea 0 Hawaii hot spot The Pacific Plate has moved northwest over the Hawaiian hot spot… …resulting in a chain of volcanic islands. The ages of the mountains suggest plate movement of about 100 mm/yr… A sharp change in direction has been dated at about 43 Ma.

PACIFIC OCEAN Washington Oregon CaliforniaNevadaUtah Idaho Montana Wyoming Yellowstone Caldera Chain Yellowstone National Park Hot spot 0.8 Ma

Yellowstone National Park Hot spot 0.8 Ma The North American Plate is moving southwest over the Yellowstone hot spot.

10 things you didn’t know about volcanoes (58:52) - Youtube

Lithosphere Outer core Mantle Plume head Core-mantle boundary Core-mantle boundary Instability at the core-mantle boundary causes a mantle plume to arise. Flood basalts Basaltic magma penetrates the lithosphere and erupts as flood basalts. Hot-spot volcano Plume tail Plate movement The plume tail may form a hot-spot volcano. Active volcano Active volcano Extinct volcano Extinct volcano Continued plate movement creates a hot- spot volcano chain.