Volcanoes: eruptive style and associated landforms
Viscosity Resistance to flow Which test tube contains the fluid with high viscosity? Left? Right?
Viscosity Which eruption was produced by high viscosity lava? What are the clues? Eruption A Eruption B
Why does one type of lava have a higher viscosity than the other?
Why does one type of lava have a higher viscosity than the other? Tectonic setting Source of lava Composition Basalt: asthenosphere and oceanic crust Andesite: sediments, water, oceanic crust and continental crust Lower percentages of silicon and oxygen Intermediate composition
The Silicon Tetrahedron Acts as a thickening agent Building block to all rock forming minerals Higher percentage = higher viscosity Rhyolite > 65% Andesite = 55-65 % Basalt < 55%
Rhyolite is the lava type with the highest percentages of silicon and oxygen Most violent eruptions
Hot spot under continental crust Notice the direction of plate movement
Andesite Intermediate composition lava
Landforms associated with viscous lava Andesitic lava produces stratovolcanoes Rhyolitic or dacitic lava produces plugs.
Mt. Rainier
Mt. St. Helens: before the 1980 eruption Bulge: plug that is pushed out by magma within the conduit.
Mt. St. Helens: after the eruption Plug dome
Mt. St. Helens: dome plug The plug is nearly the height of the Washington Monument and the width of four football fields.
Plug dome: andesitic to rhyolitic in composition
Lassen Peak Lassen Peak is a plug dome volcanic landform Built from felsic lava One of the largest on Earth Carved by glaciers during the Ice Age
Crater Lake: volcanic caldera
Caldera formation and subsequent plug Volcanic eruption Large volume of material extruded Magma chamber empties Volcano collapses into the empty magma chamber
Yellowstone: hot spot under continental crust Three large eruptions in the last 2 million, 1.3 million and 600,000 years ago Calderas formed when felsic lava produced enormous eruptions.
Yellowstone caldera formation
Long Valley Caldera An enormous eruption 760,000 years ago, forming a caldera
Landforms associated with low viscosity lavas Basaltic lava flows produce shield volcanoes and lava plains or flood basalts.
Shield volcano Mauna Loa is 9 miles high Built over a long period of time Associated with basaltic lava
Modoc Plateau, northeastern California (extension) Medicine Lake volcanic field Mt. Shasta is in the background Tectonic setting?
Columbia River Basalts Basaltic lava flows from fissures Layer upon layer of lava flows Covers continental crust Columbia River Basalts 14-16 million years old
What happened in Iceland? Eyjafjallajokull's eruption creates an ash cloud that closed Europe’s airports for weeks Shield volcano eruption under a layer of ice
Size comparison
Cinder cones: found in most setting Hawaii Short lived events made of cinders generally about 1000 feet high Mojave Desert
Composition,Viscosity and Eruptive Style Basalt Andesite Rhyolite Fluid Viscosity Pasty Eruptive Style Quiet Violent Temperature Cool Hot
The three Vs Viscosity Strombolian Icelandic Volatiles Volume Plinian
Volcanic material Pyroclastic debris Lava flow Pieces of older rock and magma Ash size to bombs Smooth or chuncky
Volcanic Explosivity Index Volume of material How high the eruption column reached How long the main eruption occurred