Volcanic and Tectonic Landforms

7/29/2019 Volcanic and Tectonic Landforms

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Visualizing Physical Geography

Copyright 2008 John Wiley and Sons Publishers Inc.

Volcanic and Tectonic Landforms


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Continental landforms are the result of endogenic and exogenicprocesses.

Endogenicprocess: works from within the Earth

Produces initial landformsUplifts; brings fresh rock to the surface

Powered by Earths internal energy

Exogenicprocess: works at Earths surfaceWears down initial landforms

Creates sequential landforms


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Volcanic Landforms

Volcanic ActivityVolcano: conical, circular structure built by accumulation of lava flows andtephra (volcanic ash)


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Volcanic Landforms

Volcanic Activity

Many volcanoes arelocated on subductionboundaries or riftzones.


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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: volcanoconstructed of multiple layers oflava and tephra (volcanic ash)


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Volcanic Landforms

Stratovolcanoes Most active stratovolcanoes on

circum-Pacific mountain belt

Associated with subduction zones Felsic lavas produce explosive

eruptionsLarge amounts of gas under highpressure

Central part of volcano mayexplode, leaving caldera: centraldepression


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Volcanic Landforms

Stratovolcanoes

Exogenic processes erodestratovolcanoes


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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, spreadsout in thin layers

Shield volcanoes are roundeddomes, with gentle slopes

Shield Volcano: low, often large, dome-like

accumulation of basalt lava flows emergingfrom long , radial fissures on flanks


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Volcanic Landforms

Shield Volcanoes

Some shield volcanoes

form overhotspots:stationary plumes ofbasaltic lava welling upfrom the mantle


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Volcanic Landforms

Shield Volcanoes

The Hawaiian chain was

formed by the movement ofthe Pacific Plate over ahotspot.

Chain of islands shows motionof the plate

Active volcanoes at thesouthern end

Guyots (sunken islands) at thenorthern end


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Volcanic Landforms

Shield Volcanoes

Basaltic lava also erupts:

Along midocean ridgesSeafloor spreadingMany volcanic islands alongmid-Atlantic Ridge

Beneath continental platesHotspot generates largevolume of basaltic lava

Forms flood basalts

Continental flood basalts,Columbia Plateau, U.S.

Basaltic lava on Heimaey Island,Iceland, on mid-Atlantic Ridge


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Volcanic Landforms

Geothermal Energy Sources

Geothermal energyis energy from the heat in the Earth

Regions near hot springs and geysers have hot water that can betapped and used to drive turbines to generate electricity.


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Tectonic Landforms

Fold Belts

Compression fromtectonic activityproduces folds in rockstrata

Anticlines: upbendsSynclines: troughs

Folds: corrugations of

strata caused by crustalcompression


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Tectonic Landforms

Fold BeltsFolds erode to form ridge-and-valley landscape

Ridges and valleys parallel

Folds may be plunging folds


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Tectonic Landforms

Faults and Fault Landforms

Fault: sharp break in rock with aslippage of the crustal block on oneside with respect to the block on theother

Fault lines may extend for manykilometers

Most major faults extend downseveral kilometers

Fault slippage varies from 1 cm to 15 m

Four main types of faults:Normal

Transcurrent

Reverse

Overthrust

T t i L df


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Tectonic Landforms


Normal faults are produced by crustal extension

T t i L df


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Tectonic Landforms


The East African Rift Valley is a graben

T t i L df


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Tectonic Landforms

Faults and Fault LandformsTranscurrentorStrike-slip Faults are producedwhen tectonic plates move past each other

horizontally

T t i L df


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Tectonic Landforms


Reverse and overthrustfaults are

produced by compression in thecrust

T t i L df


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Tectonic Landforms


Repeated faulting can produce high fault

scarps

Landforms are modified by erosion

E th k


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Earthquakes

Earthquake: a trembling orshaking of the ground

produced by passingseismic waves

Most earthquakes produced bysudden slippage along faults

Energy builds up until the faultslips, releasing seismic waves

Earthquake magnitudes may bedescribed on the Richter Scale

E th k


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Earthquakes

Earthquakes usually occur on plate boundariesLarge-magnitude earthquakes are generated along subduction zones

Transcurrent faults on transform boundaries cause moderate to strong

earthquakesSpreading plate boundaries produce moderate earthquakes

Some earthquakes occur in the centers of continents, away from plateboundaries

E th k


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Earthquakes

Earthquakes Along the San Andreas FaultSan 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

Earthquakes


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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%

Earthquakes


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Earthquakes

Seismic Sea WavesTsunami: train of sea waves triggered by an earthquake (or other seafloordisturbance) traveling over the ocean surface

Banda Aceh, Indonesia, beforeand after 2004 tsunami

Kalutara Beach, Sri Lanka,before and during 2004 tsunami

Landforms and Rock Structure


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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 asurrounding plain and that develops because itconsists of more resistant rock than the bedrock ofthe surrounding region

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Volcanic and Tectonic Landforms