THE ROCK CYCLE

VOLCANISM

I. Introduction From: Roman god of fire, Vulcan

I. Introduction From: Roman god of fire, Vulcan What is a volcano? A conical mountain formed around a vent where lava, pyroclastic materials, and gases are erupted.

I. Introduction B. Volcanic activity: Active Dormant Extinct

B. Volcanic Activity 1. Active volcanoes activity in the last few centuries Ex: Vesuvius, 79 A.D. (50 times in 2000 yr) Ex: Mt. St. Helens (1980)

B. Volcanic Activity 2. Dormant volcanoes “quiet” for the last hundred to thousands of years, but still have potential to erupt. Mt. Rainier

B. Volcanic Activity 3. Extinct volcanoes No eruption in historical times No signs of erupting again

Introduction C. Volcano Distribution Most volcanoes occur in one of three areas: Circum-Pacific (i.e. The Ring of Fire) 60% Mediterranean 20% Spreading centers (Divergent boundaries) 10 – 15%

Volcano Distribution

II. Volcanic materials Three types of material expelled from volcanoes

Volcanic materials A. Lava (“the liquid”) Molten rock

Volcanic materials A. Lava Silica affects viscosity Molten rock Silica affects viscosity Viscosity is resistance to flow

II. Volcanic materials A. Lava 1) Pahoehoe lava Basaltic lava Low viscosity

II. Volcanic materials A. Lava 1) Pahoehoe lava Basaltic lava Low viscosity Cools moderately slowly Ropelike appearance

II. Volcanic materials A. Lava 2) Aa lava (pronounced aa-aa) Basaltic lava Higher viscosity Solidifies while flowing Angular pieces

II. Volcanic materials A. Lava 3) Pillow lavas Lava extruded underwater Cools and contracts Spherical masses Ocean floor

II. Volcanic materials A. Lava (“the liquid”) B. Ash and pyroclastic material (“the solid”) Airborne material ejected by a volcano Classified based on size:

B. Ash and pyroclastic material (“the solid”) * Volcanic ash Fine ash - <0.06mm Coarse ash – 0.06mm to 2mm Composition = rock, mineral, and volcanic glass

B. Ash and pyroclastic material (“the solid”) * Cinders 2 mm and 64 mm Composition - same as ash Hazardous when falling

B. Ash and pyroclastic material (“the solid”) C) Bombs Larger than 64mm Molten rock solidifies in the air Shapes vary

II. Volcanic materials C. Volcanic gases (“the gases”) Volatiles H2S – Hydrogen sulfide H2O – Water vapor CO2 – Carbon dioxide N2 – Nitrogen HCl – Hydrochloric Acid SO2 – Sulfides

II. Volcanic materials A) Determines violence of an eruption High amount of gas = violent eruptions Violent eruptions = felsic magmas (high silica) High viscosity magma traps gas Expansion is prevented, pressure builds

II. Volcanic materials B) Effects on global climate CO2 – Greenhouse gas Particulates – Blocks sunlight

II. Volcanic materials Hazards to humans Clouds of CO2 get released Travels across the ground

III. Volcanic Landforms

III. Volcanic Landforms An erupting volcano will produce a number of distinct landforms including: A. Volcanic cones B. Flood basalts C. Calderas

A. Volcanic cones Three types of volcanic cones:

A. Volcanic cones 1) Shield volcanoes Multiple layers of basaltic lava Shallow sides due to magma’s low viscosity Gentle eruptions Wide base

A. Volcanic cones Mauna Loa volcano, Hawaii

A. Volcanic cones 2) Cinder cones – Smallest volcanic cone High viscosity Narrow Steep sides Violent eruptions shoot material straight up

A. Volcanic cones Lassen National Monument, CA

A. Volcanic cones 3) Composite or stratovolcanoes – Layered ash, lava, and mud Intermediate to felsic lava Medium steepness, due to lava’s medium viscosity Between a shield and cinder cone

A. Volcanic cones Mt. St. Helens, WA

III. Volcanic Landforms B) Flood basalts Large outpourings of basaltic lava Multiple, quiet eruptions

B) Flood basalts A portion of the Columbia Flood Basalts in WA

III. Volcanic Landforms C) Calderas Large depressions (> 1km) from violent eruptions Ugashik Caldera, AK Yellowstone

C) Calderas Two methods of formation: Volcano rapidly empties its magma chamber, and support is lost

C) Calderas Method 1 (cont.): Overlying material collapses into magma chamber Caldera forms

C) Calderas Ex: Crater Lake

C) Calderas Two methods of formation: Volcano blows its top, leaving behind a void Inside the cone.

C) Calderas Two methods of formation: Volcano blows its top, leaving behind a void Inside the cone.

IV. Volcanic hazards

IV. Volcanic hazards Lahars (hot mud flows)

IV. Volcanic hazards Lahars Sources of water Melting ice caps Excess rainfall

IV. Volcanic hazards B) Pyroclastic flows Clouds of dense gas and debris French for “glowing cloud” High speeds and high temperatures

IV. Volcanic hazards How does a pyroclastic flow form? Volcano erupts Hot debris rises Gravity takes over

IV. Volcanic hazards How does a pyroclastic flow form?(cont’d) Debris descends rapidly (200 mph) Flows down mountain slopes Travel up to 80 miles

IV. Volcanic hazards C) Tsunamis Wave generated by volcanic explosion Japanese for harbor wave

IV. Volcanic hazards Tsunamis are extremely hazardous Travel vast distances Strike with short notice Krakatoa (1883) - 36,000 people died

IV. Volcanic hazards D) Lava flows Least dangerous Lava flows pretty slowly Dangerous to property

V. Predicting Eruptions Why try to predict eruptions? Minimize damage Minimize loss of life Four ways to predict an eruption:

V. Predicting Eruptions 1) Harmonic tremors Small earthquakes From moving magma Last for hours

V. Predicting Eruptions 2) Increased gas emissions CO2 SO2 H2S Large tracts of healthy forests die off

V. Predicting Eruptions 3) Changes in mountain shape Pressure from the magma deforms the mountain Detected by tiltmeters

V. Predicting Eruptions Tiltmeter Tiltmeter measures ground tilt Stable ground = zero tilt Change from zero indicates shape change

V. Predicting Eruptions Mt. St. Helens and the orange line

V. Predicting Eruptions 4) Observe material from past eruptions Geologists map out past: Lahars Lava flows Count number of past eruptions Date each eruption Calculate periodicity

VI. Benefits of Volcanoes Soils Energy from heat Rock (Pumice) Gases for industry