1 Natural Disasters Volcanoes: Types and Eruption Styles

2 Magma Review Magma TypeBasaltAndesiteRhyolite SiO %55-65%65-75% ViscosityLowIntermediateHigh Gas contentLowIntermediateHigh Temperature °C °C °C BasaltAndesiteRhyolite

3 Types of Volcanoes Basaltic Volcanoes Shield volcanoes Cinder cones Andesitic Volcanoes stratovolcanoes Rhyolitic Volcanoes Lava domes calderas

4 Basaltic Volcanoes Shield Volcanoes Large, broad gentle slopes – resembles a “warrior’s shield” Fluid basalt able to travel great distance Low volatile (gas) content – generally non-explosive

5 Shield Examples Hawaiian Islands “Big Island” – Mauna Loa, Kilauea, and Mauna Kea Mauna Loa (largest volcano)

6 Basaltic volcanoes Cinder Cones Small size, steep slope Erupt when magma encounters groundwater Single eruptive period (months to few years) Built up by loose cinders around small crater

7 Cinder Cone Examples Amboy Crater Cima Volcanic Field Red Hill California Cinder Cones

8 Andesitic Volcanoes Stratovolcanoes Alternating layers of lava, debris, and ash Moderate volume and size Moderate to high volatile content Violently explosive Erupts repeatedly

9 Stratovolcano Examples Cascade Ranges Mt. Hood Mt. Rainier Mt. Lassen

10 Rhyolitic Volcanoes Lava Domes Rough dome with many spines Very high viscosity – magma does not travel far Low volatile (gas) content

11 Lava Domes Examples Central California Wilson Butte Panum Crater Mono Craters

12 Rhyolitic Volcanoes Giant Continental Calderas Circular, enclosed depressions Typically filled with water to form lakes Result from collapse volcanic structure –Due to underlying emptying of magma

13 Continental Caldera Example Yellowstone National Park Crater Lake, Oregon

14 Explosive Eruption Styles Hawaiian Phreatomagmatic Strombolian Vulcanian Pelean Plinian

15 Hawaiian Low-viscosity, fluid basalt Non-explosive

16 Phreatic & Phreatomagmatic Hot magma comes in contact with shallow groundwater Water heats up and erupts steam, rock fragments, and magma Violently explosive Phreatic = no new magma on surface

17 Strombolian Distinct blasts of magma Produce incandescent bombs Small tephra cone results Mildly explosive

18 Vulcanian Sustained eruption of rock or viscous magma to several km Collapse to produce pyroclastic flow Widespread tephra fall Very explosive

19 Pelean Collapse of lava dome Produce glowing avalanches (nuée ardentes) Violently explosive

20 Plinian Sustained eruption columns up to 45 km Produce widespread ash deposits Collapse of column to pyroclastic flow Violently explosive

21 Eruption Warning: Volcanic Precursors Active Volcano –Has shown activity in recorded history Extinct Volcano –Has not shown any historic activity Dormant Volcano –Has not shown activity in recorded history but shows evidence of activity in geologic past

22 Long-Term Forecasting Ancient studies help scientist assess hazards and risk posed by future volcanoes

23 Short-Term Forecasting Seismic waves Magnetic field changes Electrical Resistivity Ground Deformation Changes in groundwater heat flow Gas composition