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VOLCANISMThe Walker School
Geology
Volcanism is a Constructive Process
Atmosphere
Water
Crust
Painting of Early Earth’s Volcanism
Current Volcanism
Iceland
Hawaiian Islands
Azores
Galapagos Islands
Volcanism at Hawaii’s National Park
Notable Volcanic Eruptions
Table 5-1, p. 135
Mount Vesuvius Continues to Errupt
Fig. 5-1, p. 134
Maps of the World’s Major Volcanoes
•550 Are Currently
Active
•About 1 dozen
are erupting at
anyone time
•Responsible for
extrusive igneous
rock
Viewing Volcanoes in Google Earth
Basic Volcanic Structure
Pyroclastic Materials
Blocks
Bombs
Lapilli
Ash
Volcanic Bomb
Size
Lava Tubes at Volcanic National Park, HI
Fig. 5-3a, p. 137
Lava Tube
in Hawaii
Lava Textures
Fig. 5-4a, p. 137
Pahoehoe (pah-hoy-hoy) is
characterized by its smooth and
often ropey or wrinkly surface and
is generally formed from more
fluid lava flows.
Aa (ah-ah) is characterized by a
rough, clinkery surface and is
what most viscous and hot lava
flows look like.
Lava Composition
Felsic Lava: high percentage (>63%) of silica, and
trapped gasses; highest viscosity, lowest temperatures
Andesitic Lava: (52-63%) of silica
Mafic Lava: (45-52%) of silica + high percentage of
Magnesium (Mg); typically occur at subduction zones
Balsitic Lava: (45-52%) of silica + high percentage of
Iron (Fe); typically occur at oceanic divergent pages
Ultramafic Lava: (=<45%) of silica; lowest vicsosity,
highest temperatures
Columnar Jointing at Devil’s Post Pile
National Monument, CA
Fig. 5-5b, p. 138
Inversion of Topography
1. Lava flows into the valley
2. Lava cools and crystallizes, forming extrusive igneous rocks.
3. Areas adjacent to the flow erode more easily then the flow
4. Over time, an inversion is produced.
Fig. 5-6ab, p. 139
Craters of the Moon National Monument, IDhttp://www.nps.gov/crmo/
Fig. 5-3b, p. 137
VOLCANIC TYPES
Types of Volcanoes
Fig. 5-18, p. 149
Plutonic Bodies
Formation of a Caldera
Fig. 5-9a-d, p. 142
Crater Lake, OR Caldera
Caldera Floor of Crater Lake
Wizard Island, Crater Lake, OR
Shield Volcanos
Fig. 5-10a, p. 143
Shield Volcano, Mauna Loa, HI
•Low Viscosity Basalt Flows
•Lava fountains
•Most common in ocean basins
Cinder Cones
Fig. 5-11a, p. 144
Cinder Cones, Mojave Desert, CA
•Eruptions are short-lived.
•Large, bowl-shaped craters.
•Ash builds up rapidly.
•Few lava flows.
•Lava flows typically from base of cone.
Stratovolcanoes (Composite Cones)
Fig. 5-13a, p. 146
Stratovolcano, Mt. Rainier, WA
From Space
•Composed of layered sills.
•Lahars, or volcanic mud flows are common.
•Have steep slops near summit.
•Lava flows from andesite.
Lahar Flows, Mt. Pinatubo, Philippines
Fig. 5-14a, p. 146
Mt. Pinatubo
from Space
Lava Domes
Fig. 5-15b, p. 147
Lava Dome, Mt. St. Helens, WA
Fig. 5-15a, p. 147
•Composed of felsic magma.
•Formed from intermediate magma forced up under great pressure.
•Highly unstable, will collapse under weight of rock.
Mt. Saint Helens Eruptionhttp://www.youtube.com/watch?v=bgRnVhbfIKQ
VOLCANIC ERUPTIONS
Types of Erruptions
Fig. 5-17, p. 148
Fissure Eruptions
Generated along a linear fracture
Composed of low-viscosity melt
Commonly occur along divergent plate boundaries
Also common on the edges of large volcanoes.
Produces a curtain of fire.
Fissure eruption in Iceland
Columbia River Basalt Plateau
Fig. 5-19, p. 150
Volcanic Explosive Index
Primary Effects of Volcanoes
Pyroclastic Flows
Fumaroles
Landslides
Ash Fall
Earthquakes
High Temperatures
Secondary Effects of Explosions
Suffocation from Ash
Asphyxiation from Volcanic Gasses
Tsunamis
Temperatures Decreases
Environmental Effects
Involved in the formation of continental crust and
offset weathering and erosion
Provide nutrient rich soils
By trapping clouds at their peaks, water for
agriculture
Agriculture based cultures are attracted to their
bases
Volcanic Gasses
Water Vapor
Carbon Dioxide
Nitrogen
Sulfur Dioxide
Hydrogen Sulfide
Carbon Monoxide
Hydrogen
Chlorine
Fig. 5-2, p. 136
Gasses emitted from fumaroles at the Sulfur Works in
Lassen Volcanic National Park, CA
Effects of Volcanoes on Climate
Nucleation, condensation, and sedimentation of aerosols (acid rain)
Change in Albedo from ash cloud
Tropospheric cooling from the addition of sulfur to the stratsophere
Ozone destruction through the formation of atomic chlorine
SUPER ERUPTIONS
Supereruptionshttp://www.pbs.org/wgbh/nova/megavolcano/about.html
Discovery Questions
What does it take to be classified as a super
eruption?
When did the last one occur? Why is their
controversy about the date?
What would be the primary effects of such an
eruption?
For those who survived the initial eruption, what
would happen in the following months, or years?
How did the Toba explosion effect the evolution of
humans?
DISTRIBUTION &
MONITORING
Distribution of Volcanoes
Circum-Pacific
Belt (60%)
Mediterranean
Belt (20%)
Mid-Oceanic
Ridges (20%)
Fig. 5-20, p. 151
More common along both divergent than convergent plate boundaries.
Mainly composed of intrusive magma flows.
Composed of mafic magma that forms beneath spreading plates.
Pyroclastic materials are not common because lava is fluid.
Water pressure prevents gasses from expanding and escaping.
Alaska’s Volcanoes
Lassen Peak, CA
Largest Lava Dome in the World
Lassen Peak Diagram
Concept Art, p. 154
Mid-Atlantic Ridge & Iceland
Formation of Surtsey Island, Icelandhttp://www.youtube.com/watch?v=4MmX_i7S9u4
Important Monitoring Techniques
Fig. 5-23, p. 159
Fumarole Gas Monitoring
Chemically-selective sensors
for SO2 and CO2 measure
gas concentrations and a wind
sensor measures wind speed
and direction.
Data from solar-powered
stations are transmitted to
GOES geostationary satellite
and then down to
observatories every 10
minutes, providing near real
time data on degassing of
volcanoes
Ground Deformation Monitoring
Paint
Electronic Distance Meters
determine the horizontal movements that occur on active volcanoes
Tiltmeters
leveling surveys to measure vertical motions
Global Positioning Systems
allows us to measure horizontal motions much more accurately and conveniently, and also to estimate vertical motions in the same survey
Remote Sensing
The Advanced Very High Resolution Radiometer (AVHRR) is a space-borne sensor embarked on the NOAA family of polar orbiting platforms.
The primary purpose of these instruments is to monitor clouds and to measure the thermal emission (cooling) of the Earth.
The main difficulty associated with these investigations is to properly deal with the many limitations of these instruments, especially in the early period (sensor calibration, orbital drift, limited spectral and directional sampling, etc).
WHAT ARE BLACK
SMOKERS?
Hydrothermal Vents
Distributes heat and
drives water circulation
in the ocean through
convection
Provides energy source
in the form of hydrogen
sulfide to benthic
chemotrophs
Distributes minerals and
influences the
composition of the ocean
Hydrothermal Plume
Magma
Black smoker
Sulfide
deposit
White crab
White clamTube worms
White
smoker
Location of Major Vent Systems
Learn More About Ventshttp://www.divediscover.whoi.edu/vents/index.html
Hydrothermal Vent Chemistry
