Transcript Volcanic Landforms

Visualizing Physical Geography
by Alan Strahler and Zeeya Merali
Chapter 9
Volcanic and Tectonic Landforms
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Chapter Overview
Volcanic Landforms
Tectonic Landforms
Earthquakes
Landforms and Rock
Structure
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Continental landforms are the result of endogenic and exogenic
processes.
• Endogenic process: works from within the Earth
• Produces initial landforms
• Uplifts; brings fresh rock to the surface
• Powered by Earth’s internal energy
• Exogenic process: works at Earth’s surface
• Wears down initial landforms
• Creates sequential landforms
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Volcanic Activity
Volcano: conical, circular structure built by accumulation of lava flows and
tephra (volcanic ash)
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Volcanic Activity
Many volcanoes are
located on subduction
boundaries or rift
zones.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Stratovolcanoes
The nature of an eruption depends on the type of magma involved.
Felsic lavas associated with stratovolcanoes
•
•
•
•
Rhyolite, andesite
Thick, resistant to flow
Builds steep slopes around volcanic vents
Tall, steep cone, with crater
Stratovolcano: volcano
constructed of multiple layers of
lava and tephra (volcanic ash)
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Stratovolcanoes
• Most active stratovolcanoes on
circum-Pacific mountain belt
• Associated with subduction zones
• Felsic lavas produce explosive
eruptions
• Large amounts of gas under high
pressure
• Central part of volcano may
explode, leaving caldera: central
depression
• Stratovolcanoes may emit
“glowing avalanches”
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Stratovolcanoes
Exogenic processes erode
stratovolcanoes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Shield Volcanoes
Shield volcanoes are associated
with mafic lava (basalt)
•
•
•
•
Lava thin, not viscous
Holds little gas
Usually quiet eruptions
Lava travels long distances, spreads
out in thin layers
• Shield volcanoes are rounded
domes, with gentle slopes
Shield Volcano: low, often large, dome-like
accumulation of basalt lava flows emerging
from long , radial fissures on flanks
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Shield Volcanoes
Some shield volcanoes
form over hotspots:
stationary plumes of
basaltic lava welling up
from the mantle
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Shield Volcanoes
The Hawaiian chain was
formed by the movement of
the Pacific Plate over a
hotspot.
• Chain of islands shows motion
of the plate
• Active volcanoes at the
southern end
• Guyots (sunken islands) at the
northern end
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Shield Volcanoes
Basaltic lava also erupts:
• Along midocean ridges
• Seafloor spreading
• Many volcanic islands along
mid-Atlantic Ridge
• Beneath continental plates
• Hotspot generates large
volume of basaltic lava
• Forms flood basalts
Basaltic lava on Heimaey Island,
Iceland, on mid-Atlantic Ridge
Continental flood basalts,
Columbia Plateau, U.S.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Shield Volcanoes
Cinder cones form from basaltic lava ejected under high pressure from
a vent
• Produces tephra: particles of various sizes, ejected from a volcano
• Not usually large
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Shield Volcanoes
Erosion of shield volcanoes
differs from erosion of
stratovolcanoes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Volcanic Landforms
Geothermal Energy Sources
Geothermal energy is energy from the heat in the Earth
Regions near hot springs and geysers have hot water that can be
tapped and used to drive turbines to generate electricity.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Fold Belts
Compression from
tectonic activity
produces folds in rock
strata
Anticlines: upbends
Synclines: troughs
Folds: corrugations of
strata caused by crustal
compression
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Fold Belts
Folds erode to form ridge-and-valley landscape
• Ridges and valleys parallel
• Folds may be plunging folds
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Faults and Fault Landforms
Fault: sharp break in rock with a
slippage of the crustal block on one
side with respect to the block on the
other
• Fault lines may extend for many
kilometers
• Most major faults extend down
several kilometers
• Fault slippage varies from 1 cm to 15 m
• Four main types of faults:
• Normal
• Transcurrent
• Reverse
• Overthrust
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Faults and Fault Landforms
Normal faults are produced by crustal extension
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Faults and Fault Landforms
The East African Rift Valley is a graben
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Faults and Fault Landforms
Transcurrent or Strike-slip Faults are produced
when tectonic plates move past each other
horizontally
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Faults and Fault Landforms
Reverse and overthrust faults are
produced by compression in the
crust
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tectonic Landforms
Faults and Fault Landforms
• Repeated faulting can produce high fault
scarps
• Landforms are modified by erosion
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earthquakes
Earthquake: a trembling or
shaking of the ground
produced by passing
seismic waves
• Most earthquakes produced by
sudden slippage along faults
• Energy builds up until the fault
slips, releasing seismic waves
• Earthquake magnitudes may be
described on the Richter Scale
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earthquakes
Earthquakes usually occur on plate boundaries
•Large-magnitude earthquakes are generated along subduction zones
•Transcurrent faults on transform boundaries cause moderate to strong
earthquakes
•Spreading plate boundaries produce moderate earthquakes
•Some earthquakes occur in the centers of continents, away from plate
boundaries
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earthquakes
Earthquakes Along the San Andreas Fault
San Francisco Earthquake, 1906
•700 lives lost
•$30 billion damage
• Generated by movement on San Andreas Fault
• This portion of the San Andreas has not moved since 1906
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earthquakes
Earthquakes Along the San Andreas Fault
• Loma Prieta Quake, 1989
•62 lives lost
•$6 billion damage
•Occurred on fault near the San Andreas
•Did not fully relieve strain on San Andreas
• Southern California: likelihood of very large
earthquake within 30 years is 50%
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Earthquakes
Seismic Sea Waves
Tsunami: train of sea waves triggered by an earthquake (or other seafloor
disturbance) traveling over the ocean surface
Banda Aceh, Indonesia, before
and after 2004 tsunami
Kalutara Beach, Sri Lanka,
before and during 2004 tsunami
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landforms and Rock Structure
Rock structure controls locations of uplands and lowlands,
placement of streams, shape and heights of divides
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landforms and Rock Structure
Landforms of Horizontal Strata and Coastal Plains
Arid climate landforms: horizontal strata in an arid climate often produce
plateaus, mesas, and buttes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landforms and Rock Structure
Landforms of Horizontal Strata and Coastal Plains
On coastal plains along passive continental margins, consequent streams,
subsequent streams, and cuestas may develop
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landforms and Rock Structure
Landforms of Warped Rock Layers
Sedimentary domes are created when sedimentary strata are forced upward
into a dome
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landforms and Rock Structure
Metamorphic Belts
Folded metamorphic rocks also produce ridges (resistant rocks) and valleys
(weak rocks)
• Marble forms valleys
• Gneiss, schist, slate, quartzite form ridges and hills
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landforms and Rock Structure
Exposed Batholiths and Monadnocks
Batholiths: huge bodies of intrusive igneous rock
• Form hilly or mountainous uplands
• Monadnock: a mountain that rises out of a
surrounding plain and that develops because it
consists of more resistant rock than the bedrock of
the surrounding region
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Landform Types
•
•
•
•
•
•
Widely spaced mountains (basin and range)
High plateaus
Plains
Mountains
Hills and low plateaus
Depressions
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.