THE ROCK CYCLE VOLCANISM I Introduction From Roman

THE ROCK CYCLE

VOLCANISM

I. Introduction From: Roman god of fire, Vulcan

I. Introduction From: Roman god of fire, Vulcan A. 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

I. 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 • 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 – Molten rock – Si affects viscosity

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. 06 mm – Coarse ash – 0. 06 mm to 2 mm – 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 64 mm – Molten rock solidifies in the air – Shapes vary

II. Volcanic materials C. Volcanic gases (“the gases”) – Volatiles • • • H 2 S – Hydrogen sulfide H 2 O – Water vapor SO 2 – Sulfides CO 2 – Carbon dioxide N 2 – Nitrogen HCl – Hydrochloric Acid – Significance?

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

II. Volcanic materials B) Effects on global climate – CO 2 – Greenhouse gas – SO 2 – Blocks sunlight

II. Volcanic materials • Hazards to humans – Clouds of CO 2 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

A. Volcanic cones 1) Shield volcanoes – Tall volcanoes – 3 or 4 miles tall – Wide base – Diameter of ten of miles

A. Volcanic cones • Mauna Loa volcano, Hawaii

A. Volcanic cones 2)Cinder cones – – Smallest volcanic cone – Layered ash and cinders Ex: El Paricutin

A. Volcanic cones 2) Cinder cones – Short, narrow cone, – Steep sides – Violent eruptions

A. Volcanic cones Lassen National Monument, CA

A. Volcanic cones 3) Composite or stratovolcanoes – – Layered ash, lava, and mud – Intermediate to felsic lava – Steep sides, due to lava’s high viscosity

A. Volcanic cones 3) Composite or stratovolcanoes – – Tall volcanoes – 1 to 2 miles high – Violent eruptions

A. Volcanic cones • Mt. St. Helens, WA

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

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

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

C) Calderas Two methods of formation: Method 1: 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, OR

C) Calderas Two methods of formation: Method 2: Volcano blows its top, leaving behind a void Inside the cone.

C) Calderas Two methods of formation: Method 2: Volcano blows its top, leaving behind a void Inside the cone.

IV. Volcanic hazards

IV. Volcanic hazards A) Lahars (hot mud flows)

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

IV. Volcanic hazards B) Nuee Ardentes (Glowing Ash flows) – Clouds of dense gas and debris – French for “glowing cloud” – High speeds and high temperatures

IV. Volcanic hazards • How does a Nuee Ardente form? – Volcano erupts – Hot debris rises – Gravity takes over

IV. Volcanic hazards • How does a Nuee Ardente 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 slowly (<10 mph) – 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 – CO 2 – SO 2 – H 2 S – 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 • Benefits of volcanoes – Soils – Energy from heat – Rock (Pumice) – Gases for industry