Presentation on theme: "Volcanoes: eruptive style and associated landforms."— Presentation transcript:
Volcanoes: eruptive style and associated landforms
Viscosity Resistance to flow Which test tube contains the fluid with high viscosity? Left? Right?
Which eruption was produced by high viscosity lava? What are the clues? Viscosity Eruption AEruption B
Why does one type of lava have a higher viscosity than the other?
Tectonic setting Source of lava Composition Why does one type of lava have a higher viscosity than the other? Andesite: sediments, water, oceanic crust and continental crust Intermediate composition Basalt: asthenosphere and oceanic crust Lower percentages of silicon and oxygen
The Silicon Tetrahedron Acts as a thickening agent Building block to all rock forming minerals Higher percentage = higher viscosity Basalt < 55% Andesite = % Rhyolite > 65%
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. St. Helens: before the 1980 eruption 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 calderacaldera
Caldera formation and subsequent plug 1.Volcanic eruption 2. Large volume of material extruded 3. Magma chamber empties 4. 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.
ShieldShield volcano Mauna Loa is 9 miles high Built over a long period of time Associated with basaltic lava
Medicine Lake volcanic field Mt. Shasta is in the background –Tectonic setting? Modoc Plateau, northeastern California (extension)
Basaltic lava flows from fissures Layer upon layer of lava flows Covers continental crust million years old Columbia River Basalts
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
Cinder cones: found in most setting Hawaii Mojave Desert Short lived events made of cinders generally about 1000 feet high
Composition,Viscosity and Eruptive Style Basalt AndesiteRhyolite FluidPasty Viscosity Composition Quiet Violent Eruptive Style Hot Cool Temperature
The three Vs Viscosity Volatiles Volume Icelandic Strombolian Plinian
Volcanic material Pyroclastic debris Pieces of older rock and magma Ash size to bombs Lava flow Smooth or chuncky
Volcanic Explosivity Index Volume of material How high the eruption column reached How long the main eruption occurred