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Salt Lake Community College - GEOG 1700 - Class Notes - Week 4

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Salt Lake Community College - GEOG 1700 - Class Notes - Week 4

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background image Module 4 - Volcanoes Sunday, September 24, 2017  10:29 PM Objectives Understanding where volcanoes are located around the world and why. Determining how the composition of magma determines the explosiveness of the volcanic eruption. Explaining how volcanic activity is monitored and why. Describing the various types of volcanoes and the land-forms they create. Describing the hazards and benefits of volcanic activity.   Notes Highlight = Vocabulary Highlight = Important Terms Highlight = Examples & Places Intro Information Volcanoes can occur at divergent and convergent boundaries, or within the center of plates. 
Subducting (Convergent) Boundaries Crust heats up as it moves lower under the surface, pushing water with it Found along the Pacific Ocean Basin (aka the Ring of Fire) Middle American Trench subduction creates volcanoes in Central America Subduction of the Juan de Fuca plate under the North American plate creates volcanoes in the 
Cascades (i.e. Mount St. Helens, Mount Hood)
Subduction of the Pacific plate under the North American plate creates volcanoes in Alaska o Divergent Boundaries Magma rises to the surface as plates spread apart Found along the Mid-Atlantic Ridge, East Africa Ridge, Arabia Plates, Great Basin and Range in the 
Can also create islands (like in Iceland) o Hotspots:  a plume of hot rock rises through the mantle, pressure is released via a volcano as the 
mantle melts (in the center of plates)
Example:  Hawaii Eruption:  sudden occurrence of a violent discharge of steam and volcanic material
Each eruption is different based on eruption style, type of volcanic cone that forms, and the 
composition of the rocks found at the volcano
Volcanoes are studied by volcanologists. Currently, they are almost as difficult to predict as earthquakes
As magma moves, it can cause the earth to shake, creating earthquakes with volcanoes in the 
epicenter; increased earthquakes around a volcano may indicate an impending eruption
o The ground on or around the volcano may swell (like "blisters") Generally won’t be noticed without measuring with a tiltmeter
Gases may reach the surface prior to eruption
Satellites can be used to find high concentrations of sulfur dioxide, carbon dioxide, and 
hydrochloric acid in the air over volcanoes
Hazards & Benefits of Volcanic Activity
background image Hazards: 
Tephra:  volcanic ash that is made of tiny glass shards Cause problems with weather, pollution, plane and car engines, can block sunlight Stays in the atmosphere for years o Lahars:  mixture of lava and snow or precipitation; creates a hot mudflow that is extremely 
o Lava Flows:  lava flowing over the surface and later solidifying o Pyroclastic Flows:  caused by composite volcanoes; made of hot rock and tephra traveling 100mph  or more down mountainsides; very dangerous o Lava Bombs:  large chunks of pyroclastic material ejected from the volcano o Poisonous gas can be emitted, contributing to acid rain and ozone destruction Benefits: 
Creates fertile land nearby for agriculture o Can create minerals and precious metals (like gold, silver, nickel, copper, lead) o Beautiful landscapes leading to tourism (boosting the economy) o Geothermal Power:  heat from volcanoes used to create power and electricity; a renewable  resource o Renewable Resource:  resource providing power/electricity without creating pollution or using  limited fossil fuels Magma & Lava Composition Magma:  molten material inside the earth's surface; may never reach the surface
Mafic Magma:  low in silica, high in magnesium and iron; low viscosity  o Felsic Magma:  high silica and quartz; high viscosity o Magma Chambers:  place under the surface where magma collects; usually about 100 m under the 
Lava:  molten material on the earth's surface; may cool and turn to rock quickly
Pahoehoe Lava:  type of lava that has a ropy texture/consistency o Aa Lava:  type of lava that has a chunky texture/consistency Viscosity:  a liquid's resistance to flow (i.e. water has LOW viscosity because it flows so easily) Eruptions Erupt when mantle rock melts because of high temperatures, lowering of lithospheric pressure, and/or 
water being added.
Large Explosive Eruption:  creates more devastation than the atom bomb; eruption with felsic magma 
and extreme pressure
o Results in a large upward explosion of magma, rock, and tephra AND a pyroclastic flow down the
mountain slopes
Effusive Eruptions:  eruptions with mafic magma; gentler than explosive eruption type
People can generally be evacuated so these are less deadly o Magma pushes toward the surface through fissures, then comes out through volcanic vents Volcano Types & Activity Levels Volcanic activity is listed as 1 of 3 levels: 
Active:  currently erupting or showing signs of erupting soon o Dormant:  not current activity but has erupted recently o Extinct:  no current activity and probably won't erupt again There are 4 major types of volcanoes: 
Composite Volcanoes:  tend to occur at oceanic-to-oceanic/oceanic-to-continental boundaries 
because of subduction zones
Examples:  Mount Shasta, Mount Hood, Mount St. Helens, Mount Pinatubo Most dangerous (excluding SuperVolcanoes); contain felsic to intermediate rock; have a Large 
 eruption type
Can be so explosive that they cave in on themselves, creating a caldera Yellowstone and Crater Lake are examples of calderas.

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School: Salt Lake Community College
Department: OTHER
Course: Natural Disasters
Professor: Sally Timmins
Term: Fall 2017
Tags: Natural Hazards and volcanoes
Name: GEOG-1700, Module 4 Notes
Description: These notes cover Module 4-Volcanoes
Uploaded: 09/27/2017
3 Pages 36 Views 28 Unlocks
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