Lava Tubes at Volcanic National Park, HI
Fig. 5-3a, p. 137
Pahoehoe (pah-hoy-hoy) is Aa (ah-ah) is characterized by a
characterized by its smooth and rough, clinkery surface and is
often ropey or wrinkly surface and what most viscous and hot lava
is generally formed from more flows look like.
fluid lava flows.
Fig. 5-4a, p. 137
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,
Columnar Jointing at Devil’s Post Pile
National Monument, CA
Fig. 5-5b, p. 138
Inversion of Topography
1. Lava flows into the
2. Lava cools and
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, ID
Fig. 5-3b, p. 137
Types of Volcanoes
Fig. 5-18, p. 149
Formation of a Caldera
Fig. 5-9a-d, p. 142
Crater Lake, OR Caldera
Caldera Floor of Crater Lake
Wizard Island, Crater Lake, OR
Fig. 5-10a, p. 143
Shield Volcano, Mauna Loa, HI
•Low Viscosity Basalt Flows
•Most common in ocean basins
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
•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
Fig. 5-15b, p. 147
Lava Dome, Mt. St. Helens, WA
•Composed of felsic magma.
•Formed from intermediate magma forced up under great pressure.
•Highly unstable, will collapse under weight of rock.
Fig. 5-15a, p. 147
Mt. Saint Helens Eruption
Types of Erruptions
Fig. 5-17, p. 148
Generated along a
Composed of low-
Commonly occur along
Also common on the
edges of large Fissure eruption in Iceland
Produces a curtain of
Columbia River Basalt Plateau
Fig. 5-19, p. 150
Volcanic Explosive Index
Primary Effects of Volcanoes
Secondary Effects of Explosions
Suffocation from Ash
Asphyxiation from Volcanic Gasses
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 based cultures are attracted to their
Gasses emitted from fumaroles at the Sulfur Works in
Lassen Volcanic National Park, CA
Fig. 5-2, p. 136
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
What does it take to be classified as a super
When did the last one occur? Why is their
controversy about the date?
What would be the primary effects of such an
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
Distribution of Volcanoes
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.
Fig. 5-20, p. 151
USGS Volcano Hazards Program
Lassen Peak, CA
Largest Lava Dome in the World
Lassen Peak Diagram
Concept Art, p. 154
Mid-Atlantic Ridge & Iceland
Formation of Surtsey Island, Iceland
Important Monitoring Techniques
Fig. 5-23, p. 159
Fumarole Gas Monitoring
for SO2 and CO2 measure
gas concentrations and a wind
sensor measures wind speed
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
Ground Deformation Monitoring
Electronic Distance Meters
determine the horizontal movements
that occur on active volcanoes
leveling surveys to measure vertical
Global Positioning Systems
allows us to measure horizontal
motions much more accurately and
conveniently, and also to estimate
vertical motions in the same survey
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
WHAT ARE BLACK
Distributes heat and
drives water circulation
in the ocean through
Provides energy source
in the form of hydrogen
sulfide to benthic
Distributes minerals and
composition of the ocean
Black smoker smoker
Magma White clam
Location of Major Vent Systems
Learn More About Vents