Answer four Earth Science Essays with a minimum of 200 words in APA Format

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Foundations of Earth

Science, 6e

Lutgens, Tarbuck, & Tasa

Glacial and Arid

Landscapes Foundations, 6e - Chapter 4

Stan Hatfield

Southwestern Illinois College

Glaciers

• Glaciers are parts of two basic cycles

• Hydrologic cycle

• Rock cycle

• Glacier—A thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow

Glaciers

• Types of glaciers

• Valley (alpine) glaciers • Exist in mountainous areas

• Flow down a valley from an accumulation center at its head

• Ice sheets • Exist on a larger scale than valley

glaciers

• Two major ice sheets on Earth are over Greenland and Antarctica

Glaciers

• Types of glaciers

• Ice sheets • Often called continental ice sheets

• Ice flows out in all directions from one or more snow accumulation centers

• Other types of glaciers • Icecaps

• Outlet glaciers

• Piedmont glaciers

Present-day continental ice

sheets

How glaciers move

• Movement is referred to as flow

• Two basic types

• Plastic flow

• Occurs within the ice

• Basal slip

• Entire ice mass slipping along the

ground

• Most glaciers are thought to move by

this process

How glaciers move

• Movement is referred to as flow

• Zone of fracture

• Occurs in the uppermost 50 meters

• Tension causes crevasses to form in

brittle ice

• Rates of glacial movement • Average velocities vary considerably from one

glacier to another

How glaciers move

• Rates of glacial movement

• Rates of up to several meters per day

• Budget of a glacier

• Zone of accumulation—The area where

a glacier forms

• Elevation of the snowline varies greatly

How glaciers move

• Budget of a glacier

• Zone of wastage—The area where there

is a net loss to the glacier due to

• Melting

• Calving—The breaking off of large pieces of

ice (icebergs where the glacier has reached

the sea)

How glaciers move

• Budget of a glacier

• Balance between accumulation at the upper end of the glacier, and loss at the lower end is referred to as the glacial budget • If accumulation exceeds loss (called

ablation), the glacial front advances

• If ablation increases and/or accumulation decreases, the ice front will retreat

The glacial budget

Glacial erosion

• Glaciers are capable of great erosion and sediment transport

• Glaciers erode the land primarily in two ways

• Plucking—Lifting of rocks

• Abrasion • Rocks within the ice acting like sandpaper

to smooth and polish the surface below

Glacial erosion

• Glacial erosion

• Glacial abrasion produces

• Rock flour (pulverized rock)

• Glacial striations (grooves in the bedrock)

Glacial abrasion

Glacial erosion

• Landforms created by glacial erosion

• Erosional features of glaciated valleys • Hanging valleys

• Cirques

• Tarns

• Fiords

• Arêtes

• Horns

Glaciated

topography

The Matterhorn in

the Swiss Alps

A fiord in Norway

Glacial deposits

• Glacial drift—Refers to all sediments of

glacial origin

• Types of glacial drift

• Till—Material that is deposited directly by

the ice

• Stratified drift—Sediments laid down by

glacial meltwater

Glacial till is

typically

unstratified

and unsorted

Glacial deposits

• Landforms made of till

• Moraines

• Layers or ridges of till

• Moraines produced by alpine glaciers

• Lateral moraine

• Medial moraine

Glacial deposits

• Landforms made of till

• Other types of moraines

• End moraine—Terminal or recessional

• Ground moraine

Glacial depositional features

Glacial deposits

• Landforms made of till

• Drumlins

• Smooth, elongated, parallel hills

• Steep side faces the direction from which

the ice advanced

• Occur in clusters called drumlin fields

Glacial deposits

• Landforms made of stratified drift

• Outwash plains (with ice sheets) and valley trains (when in a valley) • Broad ramp-like surface composed of

stratified drift deposited by meltwater leaving a glacier

• Located adjacent to the downstream edge of most end moraines

• Often pockmarked with depressions called kettles

Glacial deposits

• Landforms made of stratified drift

• Ice-contact deposits

• Deposited by meltwater flowing over, within,

and at the base of motionless ice

• Features include

• Kames

• Eskers

Glaciers of the past

• Ice Age

• Ice covered 30 percent of Earth’s land area

• Ice age began between 2–3 million years ago

• Most of the major glacial episodes occurred during a division of geologic time called the Pleistocene epoch

Maximum extent of ice

during the Ice Age

Glaciers of the past

• Indirect effects of Ice Age glaciers

• Forces migration of animals and

plants

• Changes in stream courses

• Rebounding upward of the crust in

former centers of ice accumulation

• Worldwide change in sea level

• Climatic changes

Deserts

• Dry regions cover 30 percent of

Earth’s land surface

• Distribution and causes of dry lands

• Two climatic types are commonly

recognized

• Desert or arid

• Steppe or semiarid

Desert and steppe

regions of the world

Deserts

• Dry lands are concentrated in two

regions

• Subtropics

• Low-latitude deserts

• Areas of high pressure and sinking air

that is compressed and warmed

Deserts

• Dry lands are concentrated in two

regions

• Middle-latitudes

• Located in the deep interiors of continents

• High mountains in the path of the prevailing

winds produce a rainshadow desert

Rainshadow desert

Deserts

• Role of water in arid climates

• Most streambeds are dry most of the time

• Desert streams are said to be ephemeral • Carry water only during periods of

rainfall

• Different names are used for desert streams in various region

• Wash and arroyo (western United States)

• Wadi (Arabia and North Africa)

Deserts

• Role of water in arid climates

• Ephemeral streams

• Different names are used for desert streams

in various regions

• Donga (South America)

• Nullah (India)

• Desert rainfall

• Rain often occurs as heavy showers

Deserts

• Role of water in arid climates

• Desert rainfall • Because desert vegetative cover is sparse,

runoff is largely unhindered and flash floods are common

• Poorly integrated drainage systems and streams lack an extensive system of tributaries

• Most of the erosion work in a desert is done by running water

A dry channel contains water only

following heavy rain

Basin and Range: Evolution

of a desert landscape

• Characterized by interior drainage

• Landscape evolution in the Basin and Range region

• Uplift of mountains—Block faulting

• Interior drainage into basins produces • Alluvial fans

• Bajadas

• Playas and playa lakes

Basin and Range: Evolution

of a desert landscape

• Landscape evolution in the Basin and

Range region

• Ongoing erosion of the mountain mass

• Produces sediment that fills the basin

• Diminishes local relief

• Produces isolated erosional remnants

called inselbergs

Wind erosion

• Transportation of sediment by wind

• Differs from that of running water in

two ways

• Wind is less capable of picking up and

transporting coarse materials

• Wind is not confined to channels and can

spread sediment over large areas

Wind erosion

• Transportation of sediment by wind

• Mechanisms of transport

• Bedload

• Saltation—skipping and bouncing along

the surface

• Particles larger than sand are usually not

transported by wind

• Suspended load

Wind erosion

• Mechanisms of transport • Deflation

• Lifting of loose material

• Deflation produces blowouts (shallow depressions) and desert pavement (a surface of coarse pebbles and cobbles)

• Wind is a relatively insignificant erosional agent when compared to water

Creation of blowouts by deflation

Formation of

desert pavement

Wind deposits

• Wind deposits

• Significant depositional landforms are created by wind in some areas

• Two types of wind deposits • Dunes

• Mounds or ridges of sand

• Often asymmetrically shaped

• Windward slope is gently inclined and the leeward slope is the slip face

Sand dunes near

Preston Mesa, Arizona

Wind deposits

• Wind deposits

• Two types of wind deposits

• Loess

• Blankets of windblown silt

• Two primary sources are deserts and

glacial outwash deposits

• Extensive deposits occur in China and

the central United States

Loess deposits in

southern Illinois

End of Chapter 4