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Landform Geography Chapter 13. Tectonic Processes and Landforms. Volcanoes. Mts or hills w/ a conduit down into upper mantle through which magma, ash & gases are ejected 3 basic types: Cinder-cone Volcanoes Composite (strato) Volcanoes Shield Volcanoes. Volcanoes. - PowerPoint PPT Presentation
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Landform Geography
Chapter 13
Tectonic Processes
and Landforms
Volcanoes
• Mts or hills w/ a conduit down into upper mantle through which magma, ash & gases are ejected
• 3 basic types:– Cinder-cone Volcanoes– Composite (strato) Volcanoes– Shield Volcanoes Volcanoes
• Where to find volcanoes– Subduction zones, Sea-floor spreading, and Hot spots
Cinder-Cone Volcanoes
• Small, steep-sided volcano made of magma fragments & rock debris from central vent
Composite Volcanoes• Large, steep-sided volcano built up by layers of lava &
rock debris – over subduction zones – viscous, silicate magma - explosive eruptions
Cross Section Mt. Fuji
Composite Volcanoes
Pacific “Ring of Fire”• Concentration of composite volcanoes around the
Pacific Basin over subduction zones
Shield and Composite Volcanoes
Shield Volcanoes• Broad, gentle-sided volcanoes formed from low-
silica, low-viscosity magma – lava flows cool & harden to become basalt
Mauna Loa, Hawaii
Volcanic Output
• Volcanic ash consists of powder-size to sand-size particles of igneous rock material that have been blown into the air by an erupting volcano.
• An ash field is a geographic area where the ground has been blanketed by the fallout of an ash plume.
• Silicosis
• Dry ash weighs about ten times the density of fresh snow
Volcanic Ash
Volcanic Lightning
• Volcanoes produce 2 kinds of lightning:– First occurs in the smoke– The second is produced by the mouth of the
volcano
• Not all volcanoes produce lightning
Hot Spots• Stationary points in asthenosphere from which a
magma plume intermittently pushes through the crust above
• Plates move over hot spots, carrying deposits of basalt with them
• Hawaii (& the Emperor Seamount Chain) & Yellowstone have been shaped by hotspots
Formation of HawaiiEmperor Seamount Chain70 M yrs old – Pac. Plate1st moved North, then NW
HawaiiKauai Oldest – Big Island (Hawaii) still over hot spot
70 mya
Present
Hot Spot Tracks
Yellowstone Hot SpotNorth American Plate has moved west, then northwest over past
16.5 M yrs
Calderas from eruptionsin past 2 M yrs
Supervolcano• A supervolcano is an eruption that rates a magnitude
of 8 on the Volcanic Explosivity Index. • The VEI is a scale that rates eruptions on their ejected
volume, plume height and duration. The scale ranges from 0 through 8.
• Only a few dozen eruptions in all of Earth's history are known to have a VEI of 8.
• Two of those eruptions, the Lava Creek eruption (640,000 years ago) and the Huckleberry Ridge eruption (2.2 million years ago), occurred at Yellowstone.
• These eruptions were given the VEI rating because their ejected volume exceeded 1000 cubic kilometers
Geyser Cross Section
Old Faithful
Calderas• Large depression formed when a volcanic
mountain collapses after erupting
• Caldera unrest reflects tectonic, magmatic, and hydrologic processes.
• Crater Lake Caldera, Oregon
• Long Valley Caldera, California
• Carbon dioxide
• Geothermal power plants
Calderas
Earthquakes
• Sudden release of tectonic stress creates movement in Earth’s crust & shockwaves through lithosphere
• Fault – fracture between adjoining plates along which plates can move
• Focus – point in lithosphere where fault breaks
• Epicenter – point on surface directly above focus
Earthquake Processes
Earthquake Energy
• Waves released by an earthquake:– P-waves – primary, compressional waves that
travel 1.5-8 km/sec– S-waves – secondary, vertical waves that travel
60-70% slower than P waves
• Difference in arrival time of p-waves and s-waves, helps estimate distance to epicenter
• Known distance to 3 stations yields location
Triangulation to Locate ‘QuakeKnown distance to stations A, B and C shows location of epicenter
Measuring Earthquakes• Richter Scale – logarithmic measure where
each whole number represents 10X the shaking of the next smaller number
Faulting• Earthquakes occur along faults – cracks in
Earth’s crust where rocks or plates are displaced
• Fault Types:– Normal – vertical fault, diverging force– Reverse – vertical fault, compressional force – Strike-Slip – horizontal fault, blocks slide past one
another – larger scale called Transform– Overthrust – upthrown block slides over downthrown
block
Fault Types Earthquake
Normal Fault
Reverse Fault
Strike-slip Fault
San Andreas Fault(Transform Fault)
Movement
Movement