Log entry: environmental studies: earth science

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Chapter 9 Volcanic and Tectonic Landforms

Visualizing Physical Geography by Timothy Foresman and Alan Strahler

Visualizing Physical Geography

Chapter Overview

Plate Tectonics

Tectonic Activity and Earthquakes

Volcanic Activity and Landforms

Visualizing Physical Geography

Plate Tectonics

Major and minor lithospheric plates of the globes

Plate tectonics = The theory of tectonic activity, which deals with lithospheric plates and their motions

Movement of these plates is driven by heat from Earth’s core

Visualizing Physical Geography

Plate Tectonics

Types of Plate Boundaries

Extensional tectonic activity

Spreading boundary

Plates pulled apart

Compressional tectonic activity

Converging boundary

Plates pushed together

Plates move past each other

Transform boundary

Transform faults

Plate Tectonics

Diverging boundaries

A boundary where two lithospheric plates move apart

Oceanic spreading center (mid-ocean ridge)

Continental spreading centers (eventual new ocean basin)

Visualizing Physical Geography

Plate Tectonics

Transform boundaries

Plates slide past each other without colliding

The Dead Sea Fault marks the transform boundary between the African Plate on the west and the Arabian Plate on the east.

Courtesy NASA Images

Visualizing Physical Geography

Plate Tectonics

Visualizing Physical Geography

Plate Tectonics

Convergent boundaries

Subduction zones = Descent of the edge of a lithospheric plate under an adjoining plate and into the asthenosphere; density & plate thickness important

Oceanic trenches form

Mariana Trench

Japan Trench responsible for Great Tohoku earthquake of 2011

Andes mountains

Visualizing Physical Geography

Plate Tectonics

Convergent boundaries

Subduction zones

Associated with volcanoes and earthquakes

Which way does the oceanic plate move?

Visualizing Physical Geography

Plate Tectonics

Collision zones

Continental plates collide

Folds

Orogeny is a mountain- building process

Himalayas

Appalachian

Synclines

Anticlines

Overthrust faults

Which letter is an anticline and which one is a syncline?

Courtesy NASA

Visualizing Physical Geography

Plate Tectonics

Differential erosion of strata

The ways in which fold areas erode to form sequential landforms depend on the rock strengths of different strata

Weaker formations (shale and limestone) erode away to leave long, narrow ridges of hard strata (sandstone or quartzite)

Visualizing Physical Geography

Plate Tectonics

Continental suture

Two continents can converge to eliminate an ocean between them

A continental suture permanently unites the two plates, so that there is no further tectonic activity along that collision zone

Appalachian and

Ural mountains

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Faults and fault landforms

Faults occur when a sharp break associated with a slippage of the crustal block on one side of a tectonic plate with respect to another

Depth of fractures can be several kilometers

Fault slippage varies (1 cm to 15 m)

Four main types of faults

Normal

Strike-slip

Reverse

Overthrust

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Faults and fault landforms

Normal faults occur when the crust on one side of normal fault drops down relative to the other side.

Strike-slip faults are produced when tectonic plates move past each other horizontally

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Faults and fault landforms

Reverse faults are produced by compression in the crust

Overthrust faults involve mostly horizontal movement. One slice of rock rides over the adjacent ground surface.

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Faults and fault landforms

Graben = a crustal block is dropped down between two normal faults.

Horst = A crustal block

pushed up between

two normal faults.

Fault scarps: exposed rock due to fault activity (cliffs)

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Earthquakes

Earthquakes = A trembling or shaking of the ground produced by movements along a fault.

Focus = Location where fault slipped

Epicenter = The location on the Earth’s surface directly above where a fault slipped to produce an earthquake

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Earthquakes

P-waves (primary): faster

S-waves (secondary); slower moving with up and down motion

Epicenters are calculated by triangulating the readings from three different seismometer reading centers (A, B, and C), using the difference in travel times

for P and S waves.

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Earthquakes

Magnitude = the amount of energy released by an earthquake

Richter scale

Magnitude related to length of section of fault that broke

Magnitude not a direct indicator of damage; damage can be caused by

Proximity of epicenter to populated areas

Depth of focus

Type of ground

Building codes

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Tectonic Activity and Earthquakes

Tectonic environments of earthquakes

Pacific Ring of Fire

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Tectonic Activity and Earthquakes

Earthquakes

Subduction zone

Greatest earthquakes, including those in Japan, Alaska, North America, Central America, and Chile

Java Trench 9.0 earthquake and resulting tsunami (2004)

Tohoku 9.0 earthquake and tsunami (2011)

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Earthquakes

Transform boundaries

San Andreas Fault in California

1906 San Francisco Quake

1989 Loma Prieta Quake

1992 Landers Quake

Moderate to strong earthquakes



Visualizing Physical Geography

Tectonic Activity and Earthquakes

Earthquakes

California earthquakes, identified as circles with size proportional to the earthquake magnitude, are overlaid on top of delineated and mapped fault lines.

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Earthquakes

Spreading center earthquakes mostly occur along mid-ocean ridges (shallow quakes); tend to be moderate

Earthquakes can also occur away from plate boundaries; spreading plates may be cause

New Madrid 1811

Washington, DC 2011

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Tectonic Activity and Earthquakes

Earthquakes can occur along blind faults (faults that are not apparent on the Earth’s surface)

Barn, Iran 2003 Earthquake (30,000 dead)

©Christine Osborne Pictures/Alamy

Visualizing Physical Geography

Tectonic Activity and Earthquakes

Space-based instruments imaging Earth movements (InSAR)

Landform deformation of tectonic stresses after the Northridge, California earthquake

Courtesy NASA

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcano = conical, circular structure built by accumulation of lava flows and tephra (volcanic ash)

Magma (molten mineral matter)

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic activity

Many volcanoes are located on subduction boundaries or rift zones

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic activity

Hot spots = A center

of volcanic activity

thought to be located

over a rising mantle

plume.

Volcanoes not confined to plate edge

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic eruptions

When lava is forced out of a volcano violently, in the form of a volcanic eruption, it is a severe hazard

Various impacts from eruptions (ash deposition, cooling, etc.)

Mt. Pelée on the island of Martinique in 1902

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Volcanic Activity and Landforms

Volcanic eruptions

Atmospheric impacts from volcanic ash and gases have been shown to affect global weather and surface temperatures for months or years after an event

Mt. Tambora in 1815 was the year without a summer

Based on this graph, what can you conclude about the role of volcanoes on CO2 levels?

Data from NOAA

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic eruptions

Types of Volcanoes

shape, size, and explosiveness depend on the type of magma

Magma comes from two main types of igneous rocks: felsic and mafic

Two most common volcanoes:

Stratovolcano

Shield

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic eruptions

Stratovolcano = volcano constructed of multiple layers of lava and tephra (volcanic ash)

Felsic lavas (silicates)

Rhyolite, andesite

Thick, resistant to flow

Builds steep slopes around volcanic vents

Tall, steep cone, with crater

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Volcanic Activity and Landforms

Volcanic eruptions

Stratovolcano

Most active stratovolcanoes on circum-Pacific mountain belt

Associated with subduction zones

Felsic lavas produce explosive eruptions

Caldera

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Volcanic Activity and Landforms

Volcanic eruptions

Stages of stratovolcano erosion

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic eruptions

Shield Volcano = low, often large, dome-like accumulation of basalt lava flows emerging from long , radial fissures on flanks

Mafic lava (basalt) is thin, not viscous (iron, magnesium)

Holds little gas

Usually quiet eruptions

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic eruptions

Shield Volcanoes

Lava travels long distances, spreads out in thin layers

Shield volcanoes are rounded domes, with gentle slopes

Visualizing Physical Geography

Volcanic Activity and Landforms

Volcanic eruptions

Erosion of shield Volcanoes

Mauna Kea, Hawaii

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Volcanic Activity and Landforms

Other volcanic landforms

Flood basalts

Cinder cones

Wizard Island in Crater Lake

Continental flood basalts, Columbia Plateau, U.S.