landform geography earthquakes and volcanoes. earthquakes sudden release of tectonic stress creates...
TRANSCRIPT
Earthquakes
• Sudden release of tectonic stress creates movement in Earth’s crust & shockwaves through lithosphere
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
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 –
– Reverse –
– Strike-Slip –
– Overthrust –
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
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
Pacific “Ring of Fire”• Concentration of composite volcanoes around the
Pacific Basin over subduction zones
Shield Volcanoes• Broad, gentle-sided volcanoes formed from low-
silica, low-viscosity magma – lava flows cool & harden to become basalt
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 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. Plate
1st moved North, then NW
HawaiiKauai Oldest – Big Island (Hawaii) still over hot spot
70 mya
Present
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