Glacial and AridLandscapesChapter 4 LectureNatalie Bur

Glacial and Arid
Landscapes
Chapter 4 Lecture
Natalie Bursztyn
Utah State University
Foundations of Earth Science
Eighth Edition
© 2017 Pearson Education, Inc.
Explain the role of glaciers in the hydrologic and rock cycles.
Describe the different types of glaciers and their present-day
distribution.
Focus Questions 4.1
A glacier is a thick mass of ice formed over 100s or 1000s of
years
Originates by accumulation, compaction, and recrystallization
of snow
Glaciers move slowly because of gravity
Accumulate, transport, and deposit sediment
Glaciers and the Earth System

Many landscapes were shaped by glaciers during the last Ice
Age
Alps, Cape Cod, Yosemite Valley, Long Island, the Great
Lakes, fiords of Norway and Alaska…
Glaciers play an important role in both the hydrologic cycle and
the rock cycle
Precipitation can be trapped in glaciers for thousands of years
Ice is an agent of mechanical weathering
Glaciers and the Earth System
Valley or alpine glaciers occur in valleys in high mountains
Relatively small
Advance slowly (a few cm per day)
Flow down valley from an accumulation center
Generally, width is narrow relative to length
Valley (or Alpine) Glaciers
Ice sheets are found at the poles
Flow out in all directions from a center of snow accumulation
Large-scale, obscure underlying terrain
Greenland and Antarctica
Ice Sheets

Extensive ice sheets during the Last Glacial Maximum (~18,000
years ago)
Also covered North America, Europe, and Siberia
Ice sheets have advanced and retreated several times over the
last 2.6 million years
Ice Sheets
The Arctic Ocean is covered by sea ice (frozen seawater)
Floats
Ranges from a few cm to 4 m thick
Expands and contracts with the seasons
Ice shelves form when glacial ice flows into the ocean
Large, relatively flat
Attached to land and flow outward away from coast
Become thinner seaward
Ice Sheets
Ice caps
Cover uplands and high plateaus
Smaller than ice sheets but bury underlying terrain
Piedmont glaciers
Form in broad lowlands at the base of mountains
Form when glaciers emerge from the confining walls of a valley
Outlet glaciers
Extend out from ice caps and ice sheets
Other Types of Glaciers

Describe how glaciers move, the rates at which they move, and
the significance of the glacial budget.
Focus Question 4.2
Glaciers move in two ways
Plastic flow within the ice
Bonds between layers of ice are not as strong as bonds within a
layer
Layers remain intact but slide over one another
The entire body of ice slips along the ground
Uppermost 50 m of ice is the zone of fracture
Low pressure so ice behaves as a brittle solid
Tension creates cracks called crevasses

How Glaciers Move
How Glaciers Move
Glacial movement is slow
<2 m/year to >800 m/year
Occasional rapid advances (surges)
Flow is greatest at the center
Drag along valley walls and floor slows flow at edges
Observing and Measuring Movement
Glaciers form when winter snowfall is greater than summer
snowmelt
Net accumulation of snow
Snow accumulation and ice formation occur in the zone of
accumulation
Area where there is a net loss to the glacier is the zone of
wastage
Glaciers also lose ice because of calving
Generates icebergs
Budget of a Glacier: Accumulation Versus Wastage

Glacial budget
Balance or lack of balance between accumulation and wastage
Accumulation > wastage = glacial advance
Accumulation = wastage = stationary terminus
Accumulation < wastage = glacial retreat
Even if front is retreating, ice is always flowing
Glaciers are very sensitive to temperature change
Almost all glaciers are retreating at unprecedented rates

Discuss the processes of glacial erosion and the major features
created by these processes.
Focus Question 4.3
Glaciers erode and transport tremendous volumes of rock
Debris cannot settle out like sediment carried by water or wind
Capable of carrying very large pieces of debris
Glacial Erosion
Glaciers erode land in two primary ways:
Plucking
Flowing ice lifts fractured blocks of bedrock from the surface
Meltwater penetrates cracks and expands when it refreezes
Rocks break loose and are carried away by the glacier
Abrasion
Ice grinds bedrock and polishes the surface
Rock flour is finely ground bedrock
Glacial striations form when large rock fragments scrape
scratches and grooves in the bedrock
Linear features provides evidence for direction of flow
How Glaciers Erode

How Glaciers Erode
Rate of glacial erosion depends on
Rate of glacial movement
Thickness of ice
Shape, abundance, and hardness of rock fragments carried in the
ice
The erodability of the surface beneath the glacier
How Glaciers Erode
Glacial landforms created by valley (alpine) glaciers are more
pronounced than those created by ice sheets
Ice widens, deepens, and straightens valleys into
U-shaped glacial troughs
Tributary glaciers create hanging valleys
Cirques are bowl-shaped depressions at the head of a glacial
valley
Arêtes are sharp ridges and horns are pyramid-like peaks
associated with enlarged cirques
Fiords are deep, steep-sided inlets of the sea
Landforms Created by Glacial Erosion

Glacial Erosion
Glacial Erosion
Glacial Erosion
Distinguish between the two basic types of glacial deposits.
Briefly describe the features associated with each type.
Focus Questions 4.4
Material picked up by glaciers is eventually deposited when
they melt
Glacial drift
Any sediment of glacial origin
Till
Material deposited directly by ice when it melts

Stratified drift
Sorted and deposited by glacial meltwater
Glacial erratics
Boulders different from bedrock below found in the till or lying
on the surface
Types of Glacial Drift
Moraines are layers or ridges of till
Lateral moraines form along the sides of the valley
Medial moraines form between two advancing glaciers
Dark stripe of debris within the glacier
End moraines form at the terminus of a glacier
Deposited while glacial balance in equilibrium
Ground moraines are gently rolling layers of till deposited as
the terminus retreats
Moraines, Outwash Plains, and Kettles

End moraines from the last Ice Age are prominent in the
Midwest and Northeast
Kettle Moraine near Milwaukee, Long Island, and
Cape Cod
Braided meltwater streams form a broad ramp of stratified drift
Outwash plains associated with ice sheets
A valley train is confined to a mountain valley
Kettles are basins or depressions in the outwash plain formed by
buried ice that eventually melts
Typically <2 km in diameter and <10 m deep
Drumlins
Streamlined asymmetrical hills made of till
Steep side faces direction of ice advance and gentle side

indicates direction of ice flow
Occur in clusters (drumlin fields)
Eskers
Sinuous ridges of sand and gravel made by streams flowing in
tunnels underneath the ice
Kames
Steep-sided hills of stratified drift
Glacial Deposits
Glacial Deposits
Describe and explain several important effects of Ice Age
glaciers other than the formation of erosional and depositional
landforms.
Focus Question 4.5
Forced migration of animals
Alterations in stream courses
Rebounding of land
Ice sheets dam meltwater and create lakes
Proglacial lakes
World-wide change in sea level
Up to 100 m lower during the Ice Age

Pluvial lakes formed during cooler, wetter climates
Other Effects of Ice Age Glaciers
Discuss the extent of glaciation and climate variability during

the Quaternary Ice Age.
Focus Question 4.6
Last ice age began between 2 and 3 million years ago during the
Quaternary period
Antarctic Ice Sheet formed at least 30 million years ago
Ice sheets and alpine glaciers were far more extensive than they
are today
Almost 30% of Earth’s land was glacially influenced
Extent of Ice Age Glaciation
Extent of Ice Age Glaciation
Describe the general distribution and causes of Earth’s dry
lands.
Describe the role that water plays in modifying desert
landscapes.
Focus Questions 4.7

30% of Earth’s land surface is arid
Affected by many geologic processes
Mountain building, running water, wind
Deserts
Dry climate
Yearly precipitation less than the potential loss of water by
evaporation
Desert (arid)
Steppe (semiarid)
Marginal and more humid variant of desert
Transition zone that surrounds the desert
Concentrated in subtropics and middle latitudes
Distributions and Causes of Dry Lands
African, Arabian, and Australian deserts are a result of
prevailing winds
Subtropical highs in the lower latitudes
Subsiding air is compressed and warmed
Creates clear skies and ongoing dryness

Middle-latitude deserts and steppes occur in the deep interiors
of large landmasses
Little precipitation because of distance to oceans
Example of how geologic processes (mountain building) can
affect climate
Ephemeral streams only carry water during specific rainfall
events
Little vegetation to mediate runoff
Flash floods are common
Responsible for most erosion in deserts
Wind primarily transports sediment
The Role of Water in Arid Climates

The Role of Water in Arid Climates
[insert Figure 4.29 here]
Discuss the stages of landscape evolution in the Basin and
Range region of the western United States.
Focus Question 4.8
Regions with internal drainage have ephemeral streams that do
not flow out of the basin in to the ocean
E.g., Basin and Range region in western U.S.
Characterized by over 200 small fault-block mountain ranges
separated by basins
Water causes erosion following uplift
Basin and Range: The Evolution of a Mountainous Desert
Landscape
Occasional heavy rain loads rivers with sediment
Alluvial fans deposited at mouth of a canyon
A bajada is created when several alluvial fans from adjacent
canyons merge
A playa lake forms when rainfall is sufficient to cover the basin
floor

Salt flats can form when water evaporates
Continued erosion gradually diminishes local relief
Eventually only bedrock knobs called inselbergs remain
Landscape
Landscape
Landscape
Describe the ways in which wind transports sediment and the
features created by wind erosion.
Distinguish between two basic types of wind deposits.
Focus Questions 4.9
Moving air can pick up and transport loose material

Similar to a river
Velocity of wind increases with height above surface
Transports fine particles in suspension and heavier particles as
bed load
Different from a river
Less capable of transporting coarse material
Not confined to a channel
Relatively insignificant erosional agent
Wind Erosion
Deflation
Lifting and removal of loose material
Clay and silt only
Saltation
Rolling or skipping of larger particles along the surface
Blowouts
Shallow depressions caused by deflation
Desert pavement
Stony veneer left behind after deflation removes finer material
Wind Erosion
Wind Erosion

Wind Erosion
Wind can also erode via abrasion
Occurs in dry regions and along some beaches
Windblown sand polishes exposed rock surfaces
Generally <1 m above the surface
Wind Erosion
Generally two distinctive types:
Extensive blankets of silt from suspended load called loess
Mounds and ridges of sand from bed load called dunes
Wind Deposits
Loess is windblown silt
Tends to erode in vertical cliffs
Lacks bedding
Deserts and glacial deposits of stratified drift are primary
sources of silt
Wind Deposits

Sand accumulates in mounds and ridges where the path of wind
is obstructed
Many dunes have asymmetrical profiles
Leeward (sheltered) slope is steep and windward slope is gently
inclined
Sand accumulates on the slip face (leeward side) because wind
velocity is reduced just beyond the crest of the dune
Dunes migrate slowly in windward direction
Inclined layers in the windward direction are called cross
bedding
Wind Deposits
Wind Deposits
Wind Deposits

Landscapes
Fashioned by Water
Chapter 3 Lecture
Natalie Bursztyn
Eighth Edition
Three important external processes.
Describe where they fit into the rock cycle.
Focus Questions 3.1
2
External processes
Occur at or near Earth’s surface
Powered by energy from the Sun
Internal processes
Powered by energy from Earth’s interior
Earth’s External Processes
3
External processes include:

Weathering
Disintegration and decomposition of rock
Mass wasting
Transfer of rock and soil downslope under influence of gravity
Erosion
Physical removal of material by a mobile agent (e.g., flowing
water, waves, wind, ice)
Earth’s External Processes
4
Explain the role of mass wasting in the development of valleys.
Discuss the factors that trigger and influence mass-wasting
processes.
Focus Questions 3.2
5
Earth’s surface is covered by slopes
Slopes are unstable
Gravity causes material to move downslope
This movement is called mass wasting
May be slow and imperceptible, or catastrophic
Does not require a transporting medium
Mass Wasting: The Work of Gravity

6
Mass Wasting: The Work of Gravity
7
Mass Wasting and Landform Development
8
Landform evolution:
Weathering breaks rocks apart
Mass wasting transfers materials downslope
Erosion (transportation) carries the materials away
Most sediment is eventually transported to the sea
Mass wasting shapes stream valleys
Most common landform
Generally much wider than they are deep

Mass wasting increases width
Eventually transforms steep, rugged landscapes into gentle,
subdued terrain
9
10
Gravity is the controlling force
Other factors overcome inertia to create downslope motion
Slope material is gradually weakened
Slope gets closer and closer to being unstable until a trigger
initiates downslope movement
Saturation with water
Oversteepening
Removal of vegetation
Earthquakes
Controls and Triggers of Mass Wasting

11
Saturation
Water in pore space reduces cohesion and allows particles to
slide
Water adds weight to sediment
Oversteepening
Unconsolidated sediment forms a stable slope at a certain angle
of repose depending on the size and shape of the particles
Stream undercutting a valley
Waves undercutting a cliff
Human activity
12
Removal of vegetation root systems that bind sediment
Forest fires, deforestation, development, farming
Earthquakes can dislodge rock and unconsolidated material
Many mass wasting events occur without an identifiable trigger

14
List the hydrosphere’s major reservoirs.
Describe the different paths that water takes through the
hydrologic cycle.
Focus Questions 3.3
16
Water moves between the ocean, atmosphere, and land via the
hydrologic cycle
Hydrosphere is all of the reservoirs where water is held
Oceans
Glaciers
Rivers
Lakes
Air
Rock
Soil

Living tissues
The Hydrologic Cycle
17
18
96.5% of hydrosphere is the global ocean
1.76% is ice sheets and glaciers
~2% is lakes, streams, groundwater, and atmosphere
19
Hydrologic cycle is powered by the Sun
Water enters atmosphere from the oceans via evaporation
Winds transport water through the atmosphere
Precipitation either falls to the ocean or continents

Precipitation to the oceans completes the hydrologic cycle
Precipitation to the continents must return to the ocean
20
Some water soaks into the ground (infiltration)
Surplus water flows over the surface (runoff)
Water absorbed by plants is eventually released via
transpiration
Evapotranspiration is the combined effects of evaporation and
transpiration
Precipitation in cold regions becomes part of glaciers
Significant reservoirs: melting all glaciers would cause sea
level rise of dozens of meters
21
Hydrologic cycle is balanced
Average annual precipitation equals amount of water entering
the atmosphere from evapotranspiration
Precipitation exceeds evaporation over land
Evaporation exceeds precipitation over oceans

22
Describe the nature of drainage basins and river systems.
Focus Question 3.4
23
Precipitation that forms runoff depends on:
Intensity and duration of rainfall
Amount of water already in the soil
Nature of the surface material
Slope of the land
Extent and type of vegetation
Running Water
24
Runoff starts as unconfined thin sheets across hillslopes
Flow develops threads of current in tiny channels called rills
Rills converge to form gullies
Gullies converge to form streams and rivers that carry water

from broad areas
Running Water
25
Running Water
26
Drainage basins (separated by divides) are the land area that
contribute water to a river system
Divides vary in scale
Drainage Basins
27
A river system carries water from an entire drainage basin
Includes three zones:
Sediment production (erosion dominant)

Where most water and sediment is derived
Headwater regions
Sediment transport
Transportation through the channel network occurs via trunk
streams
Sediment deposition
Rivers slow when they enter a body of water; sediment
accumulates forming a delta
River Systems
28
River Systems
29
Discuss streamflow and the factors that cause it to change.
Focus Question 3.5
30

Water flow in slow-moving streams can be laminar
Moves in roughly straight-line paths parallel to stream channel
Most streamflow is turbulent
Water moves erratically in a swirling motion
Lifts sediment from streambed
Increasing flow velocity increases turbidity
Streamflow Characteristics
31
Streamflow
Flow velocity varies along a stream and through time
Flow velocity depends on:
Channel slope or gradient
Channel size and cross-sectional shape
Channel roughness
Amount of water flowing in the channel
Factors Affecting Flow Velocity

33
Gradient is the vertical drop over a specified distance
Varies from stream to stream and over a single stream’s length
Steeper gradient provides more energy for flow
Shape, size, and roughness of channel affect the amount of
friction between channel and water
Higher friction creates turbulence and slower flow
Discharge is the volume of water flowing past a certain point in
a given unit of time (m3/s)
Intermittent streams only flow during wet periods
Ephemeral streams carry water after heavy rainfall
Factors Affecting Flow Velocity
34
The cross-sectional view of a stream from headwaters to mouth
is called longitudinal profile
Overall shape is concave curve with local irregularities
Gradient, sediment size, and channel roughness decreases from
head to mouth
Discharge and channel size increases
Flow velocity increases
Changes from Upstream to Downstream
35

36
Outline the ways in which streams erode, transport, and deposit
sediment.
Focus Question 3.6
38
Streams are an important erosional agent
The Work of Running Water

39
Raindrops knock sediment particles loose
Flow of water in a stream can dislodge and lift particles from
the channel
Erodes poorly consolidated material quickly
Can undercut banks
Hydraulic force can also cut bedrock
Enhanced by particles carried in water
Swirling pebbles can carve potholes in channel floors
Stream Erosion
40
Stream Erosion
41
Stream Erosion

Streams transport sediment in three ways:
Dissolved load is material in solution
Delivered by groundwater
Not effected by velocity
Suspended load is material suspended in the water
Clay and silt particles
Larger particles can be moved during floods
Largest component of load
Bed load is material moving along the channel bed
Sand, gravel, large boulders
Only in motion intermittently
Smaller particles move via saltation
Larger particles roll or slide
Transportation of Sediment by Stream
43
Transportation of Sediment by Streams
Capacity is the maximum load of solid particles a stream can
transport per unit time
Increases with discharge

Competence is a stream’s ability to transport particles based on
size
Increases with flow velocity
Transportation of Sediment by Streams
45
As flow decreases competence is reduced
Particles settle when flow reaches critical settling velocity for
that particle size
Sorting separates particles of various sizes
Alluvium is material deposited by a stream
Deposition of Sediment by Streams
46
Contrast bedrock and alluvial stream channels.
Distinguish between two types of alluvial channels.
Focus Questions 3.7
47

Streamflow is confined to a channel
Two types of stream channels:
Bedrock channels are actively cut into solid rock
Alluvial channels are composed of unconsolidated sediment
Stream Channels
48
Bedrock channels are cut into rock
Common in headwaters with steep gradient
Transport coarse particles
Alternate between gentle gradients (alluvium accumulates) and
steep segments (bedrock is cut)
Rapids and waterfalls common
Channel pattern is controlled by underlying geologic structure
Often winding and irregular
Bedrock Channels
49
Alluvial channels are composed of loosely consolidated
sediment
Continually being eroded, transported, and redeposited
Shape is controlled by average sediment size, gradient, and
discharge

Two common types
Meandering channels
Braided channels
Alluvial Channels
50
Meandering channels have sweeping bends called meanders
High suspended load
Deep, smooth channels
Banks are resistant to erosion
Most erosion occurs on the outside of the meander, or the cut
bank, where velocity is highest
Sediment is deposited along the inside of the meander where
turbulence and velocity are low, forming point bars
Meanders migrate laterally and downstream
May form a cutoff and oxbow lake through narrow neck of land
Alluvial Channels
51
Alluvial Channels

Alluvial Channels
Braided Channels are a complex network of converging and
diverging channels
Form where most of stream load is coarse (sand and gravel) and
discharge is variable
Wide and shallow (bank material erodes easily)
Common at the end of glaciers
Alluvial Channels
54
Alluvial Channels
Contrast narrow V-shaped valleys, broad valleys with
floodplains, and valleys that display incised meanders.
Focus Question 3.8

56
A stream valley is the channel and surrounding terrain that
contributes water to the stream
Includes valley bottom and sloping walls
Top is generally broader than channel width because of mass
wasting
Divided into two general types:
Narrow, V-shaped valleys
Wide valleys with flat floors
Shaping Stream Valleys
Base level is the lower limit to how deep a stream can erode
Usually occurs where a stream enters another body of water
Velocity and ability to erode are greatly reduced
Sea level is the ultimate base level
Temporary or local base level includes lakes, resistant rock
layers, main streams, etc.
Change in base level causes readjustment of stream
Base Level and Stream Erosion
Base Level and Stream Erosion

Downcutting is dominant when gradient is steep and channel is
above base level
Abrasion and hydraulic power
Produces V-shaped valley with steep sides
Rapids and waterfalls common
Valley Deepening
Valley Deepening
Downward erosion becomes less dominant as channel reaches
base level
Channel becomes meandering
Lateral erosion creates a broad, flat valley floor called a
floodplain
Valley Widening
Valley Widening

Incised meanders flow in steep, narrow valleys
Meanders develop when stream is near base level, but base level
falls and stream starts downcutting again
Sea level fall
Uplift
Stream terraces are the remnants of former floodplains
Form after river adjusts to relative drop in base level then
floods again
Floodplain is produced at a level below the old one
Incised Meanders and Stream Terraces
Incised Meanders and Stream Terraces
Discuss the formation of deltas and natural levees.
Focus Question 3.9
66

Streams transport sediment and deposit it downstream
Bars are deposits of sand and gravel
Temporary: material will eventually be carried to the ocean
Longer life span depositional features:
Deltas
Natural levees
Depositional Landforms
Deltas form where streams enter still bodies of water
Flow decreases and sediment falls
Delta grows outward and gradient lessens
Channel chokes with sediment, divides, and moves to higher-
gradient areas
Distributaries carry water and sediment away from main channel
Deltas
Deltas
Deltas

Natural levees are built by successive floods on rivers in broad
floodplains
Flow decreases when streams overflow
Coarse sediment deposited in thin strips parallel to channels
Fine sediment distributed across floodplain
Back swamps form because drainage is poor behind levees
Yazoo tributaries parallel the river until they can breach the
levee
Natural Levees
Natural Levees
Discuss the causes of floods and some common flood control
measures.
Focus Question 3.10
73
Floods occur when stream discharge exceeds channel capacity
Among most common and most destructive natural hazards

Floods and Flood Control
Most floods occur because of weather
Snowmelt, heavy rains over large regions
Flash floods
Limited geographic extent
Influenced by rainfall intensity, surface conditions, and
topography
Common in urban areas (rapid runoff)
Failure of dams or artificial levees
Causes of Floods
Causes of Floods
Floods can be controlled by:
Artificial levees
Earthen mounds increase volume of water the channel can hold
Flood control dams
Store flood water and let it out slowly
Channelization
Artificial cutoffs shorten the stream and increase gradient and
velocity

Nonstructural approaches may be more efficient
Flood Control
Discuss the importance of groundwater.
Describe its distribution and movement.
Focus Questions 3.11
78
Groundwater exists in tiny pore spaces between grains of soil
and sediment plus narrow joints and fractures in bedrock
Groundwater: Water Beneath the Surface
Groundwater is the largest reservoir of freshwater readily
available to humans
Source of 40% of water
Drinking water for ~44% of population
40% of irrigation water
25% of water used in industry
Overuse can cause streamflow depletion, land subsidence, and
increased pumping cost
The Importance of Groundwater

The Importance of Groundwater
Important erosional agent
Forms sinkholes and caves
Stabilizes streamflow
Groundwater’s Geologic Roles
Comes from infiltration of rainfall into the ground
Amount is influenced by slope, surface material, intensity of
rainfall, vegetation
Belt of soil moisture
Film of water on soil particles near the surface
Zone of saturation
All pore space is filled with water: groundwater
Upper limit is water table
Area above the water table is called the unsaturated zone
Distribution of Groundwater

Water table is irregular
Subdued replica of the surface
Highest below hills
Contributing factors:
Groundwater moves slowly
Water “piles up” between stream valleys
Variations in rainfall
Changes in permeability of sediment
Water table falls during droughts
Porosity
Percentage of total volume of rock or sediment that consists of
open pore space
Spaces between particles, joints, faults, dissolution cavities,
vesicles
Depends on size and shape, packing, and sorting of grains
10–50% in sediment
Quantity of groundwater depends on porosity
Factors Influencing the Storage and Movement of Groundwater

Permeability
A material’s ability to transmit fluid
If spaces are too small, water can’t move through
Aquitards
Impermeable clay layers that prevent water movement
Aquifers
Rock or sediment that water moves through easily
Groundwater moves slowly from pore to pore
Typical rate is a few cm/day
Moves from high water table to low water table because of
gravity
Usually towards a stream channel, lake, or spring
Pressure increases with depth in zone of saturation
Groundwater Movement
Groundwater Movement

Compare and contrast springs, wells, and artesian systems.
Focus Question 3.12
91
A spring is a natural outflow of groundwater
Occurs where the water table intersects Earth’s surface
Aquitard prevents downward movement of water
A perched water table is a localized zone of saturation above an
aquitard
Springs
Springs
A well is a hole drilled into the zone of saturation to remove
groundwater
Drawdown is the lowering of a water table when water is
withdrawn

Decreases with increasing distance from the well
Creates a cone of depression
Wells
Wells
An artesian system
Free flowing groundwater from an outlet far above the water
table
A confined water table
The aquifer is inclined
Aquitards border above and below an aquifer
Increased pressure in a confined water table causes water to rise
and create an artesian system
Artesian Systems
Springs, Wells, and Artesian Systems

Springs, Wells, and Artesian Systems
List and discuss three important environmental problems
associated with groundwater.
Focus Question 3.13
99
Overuse threatens groundwater supply
Excessive groundwater withdrawal causes land surface to sink
Contamination
Environmental Problems of Groundwater
Groundwater system is at equilibrium
Imbalance raises or lowers water table
Long-term drop can occur with a prolonged drought of an
increase in discharge or withdrawal
Depletion of groundwater can be sever in regions of intense
irrigation
Treating Groundwater as a Nonrenewable Resource

Treating Groundwater as a Nonrenewable Resource
Ground subsidence occurs when water is removed faster than it
is replenished
Pronounced in areas underlain by thick layers of loose
sediments
Land Subsidence Caused by Groundwater Withdrawal
Common sources of contamination include septic tanks, sewer
systems, and farm wastes
Purification by natural processes can occur with correct aquifer
composition
Sand or permeable sandstone
Once pollution is identified water supply can be abandoned or
treated
Groundwater Contamination

Explain the formation of caverns and the development of karst
topography.
Focus Question 3.14
107
Most groundwater contains carbonic acid
CO2 dissolved from air and decaying plants
Dissolves limestone
Forms caverns, sinkholes, and karst landscapes
The Geologic Work of Groundwater
Caverns form due to the erosional work of groundwater
Created in the zone of saturation
Dissolved load is discharged into streams

Decorated by calcium carbonate deposits
Form when cavern is above water table
Stalactites hang from the ceiling
Stalagmites develop upward from the floor
Caverns
Caverns
Karst topography results from groundwater dissolution
Common in Kentucky, Tennessee, Alabama, Indiana, and
Florida
Not enough groundwater in arid or semiarid regions
Karst Topography
Sinkholes, or sinks, are depressions where limestone has been
dissolved

Tower karst landscapes have isolated,
steep-sided hills
Rocks: Materials
of the Solid Earth
Chapter 2 Lecture
Natalie Bursztyn
Eighth Edition
1
Sketch, label, and explain the rock cycle.
Focus Question 2.1

Focus Question 2.1
The rock cycle describes the interactions between the
components of the Earth system
Origin of igneous, sedimentary, and metamorphic rocks and how
they are connected
Any rock can be transformed into any other rock type under the
right conditions
Earth as a System: The Rock Cycle
The rock cycle begins with magma
Forms from melting in Earth’s crust and upper mantle
Less dense magma rises toward the surface
Erupts at surface as lava or cools within crust
Cooling is called crystallization or solidification
Igneous rocks are crystallized from
Magma (within the crust)
Or lava (at Earth’s surface)
The Basic Cycle

Igneous rocks exposed at Earth's surface undergo weathering
Atmosphere decomposes rock
Generates loose material or dissolves it
Loose material is called sediment
Transported by gravity, running water, glaciers, wind, waves,
etc.
Most sediment is transported to the ocean, but some is deposited
in other environments
The Basic Cycle
Deposited sediment undergoes lithification
“Conversion into rock” by
Compaction
Cementation
Deformed by great heat and pressure if deeply buried or
incorporated into a mountain chain
Metamorphism
Eventually enough heat will melt the rock and generate magma
The Basic Cycle
The Basic Cycle

Rocks are not stable unchanging masses over geologic time
scales
Rock cycle happens over millions or billions of years
Different stages of the rock cycle are occurring today all over
Earth’s surface
New igneous rocks are forming in Hawaii
The Colorado Rockies are eroding and material is being carried
to the Gulf of Mexico
The Basic Cycle
Rocks do not always go through the rock cycle from igneous to
sedimentary to metamorphic
Igneous rocks may remain deeply buried and then become
metamorphosed
Sedimentary and metamorphic rocks may be uplifted and eroded
into sediment instead of melted
The rock cycle is driven by Earth’s internal heat and external
processes, including weathering and erosion
Alternative Paths
Describe the two criteria used to classify igneous rocks.
Explain how the rate of cooling influences the crystal size of
minerals.
Focus Questions 2.2

Igneous rocks form when magma or lava cools and crystallizes
Magma is generated most commonl y by melting in the mantle,
but some is generated by melting the crust
Rises because it is less dense than surrounding rock
Magma that reaches Earth’s surface is known as lava
Igneous Rocks: “Formed by Fire”
Solidification of lava at Earth’s surface creates extrusive or
volcanic igneous rocks
Most volcanic eruptions are not violent
Abundant in the northwest (Cascades, Columbia Plateau)
Many oceanic islands are volcanic (Hawaii)
Most magma never reaches the surface, and instead solidifies as
intrusive or plutonic igneous rocks
Only exposed at the surface by uplift and erosion
Mount Washington (New Hampshire)
Stone Mountain (Georgia)
Mount Rushmore and the Black Hills (South Dakota)
Yosemite National Park (California)

Magma contains ions including silicon and oxygen, gas (water
vapor) confined by pressure, and some solid crystals
Crystallization occurs as mobile ions arrange into orderly
patterns during cooling
As cooling continues, more ions are added to the crystals until
all of the liquid becomes a solid mass of interlocking crystals
From Magma to Crystalline Rock
Rate of cooling strongly influences crystal size
Slow cooling results in fewer, larger crystals
Quick cooling results in a large number of small intergrown
crystals
Instantaneous cooling (“quenching”) results in randomly
distributed atoms, no crystal growth, and formation of volcanic
glass
Volcanic ash is actually tiny shards of glass
Crystallization is also influenced by magma composition and
dissolved gas
From Magma to Crystalline Rock

Igneous rocks are mainly composed of silicate minerals
Silicon and oxygen + Al, Ca, Na, K, Mg, and Fe make up 98%
of most magmas
Also includes small amounts of trace elements
Titanium, manganese, gold, silver, uranium, etc.
During crystallization, these elements combine to form two
major groups of silicate minerals
Igneous Compositions
Dark silicates are rich in iron and/or magnesium and relatively
low in silica
Olivine, pyroxene, amphibole, biotite mica
Light silicates contain greater amounts of potassium, sodium
and calcium and are richer in silica
Quartz, muscovite mica, feldspars
Feldspars are most abundant mineral group
40% of most igneous rocks
Igneous rocks can be divided into broad groups according to
proportions of light and dark minerals

Granitic (felsic) rocks
Igneous rocks of granitic composition are made up almost
entirely of light-colored silicates
Quartz and potassium feldspar
Felsic = feldspar + silica
Most contain ~10% dark silicate minerals
Biotite mica, amphibole
~70% silica
Major constituent of continental crust
Basaltic (mafic) rocks
Contain at least 45% dark silicate minerals and Ca-rich
plagioclase but no quartz
Mafic = magnesium + ferrum (iron)
Darker and more dense than granitic rocks because of iron
content
Andesitic (intermediate) rocks
Andesitic falls between granitic and basaltic composition
Mixture of both light- and dark-colored minerals
Contain at least 25% dark-silicate minerals
Amphibole and plagioclase feldspar
Associated with volcanic activity at continental margins

Ultramafic rocks
Contain mostly dark-colored minerals
Olivine and pyroxene
For example, peridotite and dunite
Rare at Earth’s surface
Main constituent of upper mantle
The texture of a rock is described based on the size, shape, and
arrangement of mineral grains
Texture can be used to make inferences about a rock’s origin,
for example:
Large crystals indicate slow cooling
Slow cooling is common in magma chambers deep in the crust
A rock with large crystals probably formed deep in the crust
What Can Igneous Textures Tell Us?
Fine-grained texture
Cooled rapidly at the surface or in small masses in the upper
crust
Individual crystals are too small to see with the naked eye
Coarse-grained texture
Solidified at depth while insulated by surrounding rock
Masses of interlocking crystals roughly the same size (large
enough to be seen by the naked eye)

Porphyritic texture
Different minerals crystallize under different temperature and
pressure conditions
One mineral can reach a large size before other minerals start to
form
Large crystals (phenocrysts) in a matrix of smaller crystals
(groundmass)
Vesicular texture
Exhibits voids left by gas bubbles that remained when lava
solidified
Form in upper zone of a lava flow
Glassy texture
Develops when rocks cool rapidly
Ions freeze in place before they can arrange themselves in an
orderly crystalline structure
Pyroclastic (fragmental) texture

Composed of individual rock fragments ejected during
explosive volcanic eruptions
Particles could be very fine ash, molten blobs, or large angular
blocks
Igneous rocks are classified by texture and mineral composition
Texture results from cooling history
Mineral composition derives from parent magma and
environment of crystallization
Common Igneous Rocks
Granite
Coarse-grained

Forms when magma solidified slowly at depth
Uplifted during mountain building
Rhyolite
Extrusive fine-grained equivalent of granite
Light-colored silicates, usually buff, pink, or light grey
Frequently contains voids and fragments of volcanic glass
Cooled rapidly at Earth’s surface
Obsidian
Natural volcanic glass
Dark in color (from metallic ions), but felsic composition

Pumice
Vesicular volcanic glass
Gas escape from molten lava forms a frothy, gray rock
Many pieces float in water because of vesicles
Andesite
Medium-gray extrusive igneous rock
Fine-grained or porphyritic with phenocrysts of plagioclase
feldspar or amphibole
Major constituent of volcanos along the Pacific Rim
Andes Mountains
Cascade Range
Diorite
Coarse-grained intrusive equivalent of andesite
Few or no visible quartz crystals
Basalt
Most common extrusive igneous rock
Dark green to black, fine-grained
Contains pyroxene, olivine, and plagioclase feldspar
Relatively common at Earth’s surface
Volcanic islands (e.g., Hawaii, Iceland)
Upper layers of the oceanic crust
Central Oregon and Washington
Gabbro

Coarse-grained intrusive equivalent of basalt
Not commonly exposed at Earth’s surface
Significant component of oceanic crust
Magma can evolve
Different rock types can be generated from the same melt
Bowen’s reaction series describes which minerals solidify at
specific temperatures
First to crystallize is olivine, then pyroxene and plagioclase
Amphibole and biotite at intermediate temperatures
Muscovite and potassium feldspar during late cooling
Quartz is last to solidify
Minerals that form in the same temperature range tend to be
associated in the same igneous rocks
How Different Igneous Rocks Form

Magmatic differentiation is the formation of one or more
secondary magmas from a single parent magma
Explains diversity of igneous rocks
Magma composition continually changes during cooling
As crystals form, certain elements are selectively removed,
resulting in a depleted magma
Crystal settling occurs when dense minerals sink to the bottom
of a magma chamber
Define weathering.
Distinguish between the two main categories of weathering.
Focus Questions 2.3

Weathering is the transformation of a rock to reach equilibrium
with its environment
Natural response of materials to a new environment
Two basic categories: mechanical and chemical
Generally occur simultaneously
Erosion transports weathered rock
Weathering of Rocks to Form Sediment
Mechanical weathering is the process of breaking down rocks
into smaller pieces
Each piece retains the same physical properties of the original
material
Increases surface area available for chemical weathering
Mechanical Weathering
Frost wedging
Ice expands ~9% when it freezes
Traditional explanation: water fills cracks in rocks and expands

Recent research: lenses of ice grow within cracks and pore
spaces of rock until rock is weakened and fractures
Salt Crystal Growth
Sea spray or salty groundwater evaporate in rock’s crevices and
pore spaces
Salt crystals grow larger and weaken the rock by pushing apart
surrounding grains or enlarging tiny cracks
Common on rocky shorelines and in arid regions
Sheeting occurs when concentric slabs of intrusive igneous rock
break loose
Removal of overlying rock reduces pressure and outer layers
expand and separate
Continued weathering results in exfoliation domes

Biological activity also breaks rocks apart
Plant roots grow into cracks and wedge the rock apart
Burrowing animals expose rock to increased weathering
Decaying organisms produce acids, which contribute to
chemical weathering
Chemical weathering alters the internal structure of minerals
Elements are removed or added
Original rock is transformed into new stable material
Makes outer portions of some rocks more susceptible to
mechanical weathering
Water is most important agent of chemical weathering
Oxygen dissolved in water causes oxidation
Carbon dioxide dissolved in water is carbonic acid
Feldspar minerals are broken down into clay minerals
Silica is carried away by ground water
Quartz is very resistant to chemical weathering
Chemical Weathering

Chemical weathering of a silicate rock by carbonic acid
Feldspar minerals are broken down into clay minerals
Silica is carried away by ground water
Quartz is very resistant to chemical weathering
Products of Chemical Weathering
Products of Chemical Weathering
List and describe the different categories of sedimentary rocks.
Discuss the processes that change sediment into sedimentary
rock.
Focus Questions 2.4
Sedimentary rocks form after weathering breaks rocks down,
gravity and erosional agents transport and deposit the sediment,
and the sediment becomes lithified
Most sedimentary rock is deposited by solid material settling
out of a fluid
Sedimentary rocks make up ~5% of Earth’s outer 10 miles, but
account for 75% of all continental rock outcrops

Used to reconstruct details about Earth’s history
Economically important
Coal, petroleum and natural gas, metals, fertilizer, construction
materials
Sedimentary Rocks: Compacted and Cemented Sediment
Sedimentary Rocks: Compacted and Cemented Sediment
Sedimentary rocks are classified in two groups
Detrital sedimentary rocks form from solid particles weathered
from other rocks
Chemical and biochemical sedimentary form from ions carried
in solution
Types of Sedimentary Rocks
Detrital sedimentary rocks
Contain a wide variety of minerals and rock fragments
Clay and quartz are most common
Distinguished by particle size
Also useful for determining environment of deposition
Higher energy carries larger particles
Mineral composition is also used to classify detrital
sedimentary rocks

Chemical sedimentary rocks
Water carries ions in solution
Solid material precipitates to form chemical sediments
E.g. salt left behind when saltwater evaporates
Materials precipitated by organisms are known as biochemical
sediments
E.g. shells and hard parts
Limestone is composed of calcite (CaCO3)
Nearly 90% is formed by organisms
Examples of chemical sedimentary rocks:

Coquina: loosely cemented shell fragments
Chalk: hard parts of microscopic organisms
Travertine: inorganic limestone that forms in caves
Chert, flint, jasper, and agate: microcrystalline quartz
Salt and gypsum form in evaporite deposits
Coal consists mostly of organic matter

Lithification is the process by which sediment is transformed
into sedimentary rock
Compaction occurs when grains are pressed closer together so
that pore space is reduced
Weight of accumulated sediment
Most significant in fine-grained rocks
Cementation occurs when water containing dissolved minerals
moves through pores
Cement precipitates, fills pores, and joins particles together
Calcite, silica, and iron oxide are common cements
Significant in coarse-grained rocks
Lithification of Sediment
Sedimentary rocks form in layers called strata
or beds
Characteristic of sedimentary rocks
Thickness ranges from microscopic to tens of meters
Bedding planes ark the end of one episode of sedimentation and
the beginning of another
Fossils are traces or remains of life found in some sedimentary
rocks

Important clues of ancient environment
Can be used to match up rocks of the same age found in
different places
Features of Sedimentary Rocks
Sedimentary rocks provide evidence for deciphering past
environments
Features of Sedimentary Rocks
Define metamorphism.
Explain how metamorphic rocks form.
Describe the agents of metamorphism.
Focus Questions 2.5
Metamorphic rocks are produced when preexisting parent rock
is transformed
Parent rock can be igneous, sedimentary, or metamorphic
Metamorphism occurs when parent rock is subjected to a
different physical or chemical environment
Elevated temperature and pressure
Changes mineralogy, texture, and sometimes chemical
composition
Equilibrium with new environment

Metamorphism progresses incrementally
Low-grade (slight changes) to high-grade (substantial changes)
Metamorphic Rocks: New Rock from Old
Most metamorphism occurs in one of two settings:
Contact metamorphism
Rock temperature increases because of intruding magma
Regional metamorphism
Pressure and high temperature during mountain building
Agents of metamorphism
Heat (from intrusion of magma or burial)
Chemical reactions and recrystallization of new minerals
Confining pressure (equal in all directions because of burial)
Compaction and recrystallization of new minerals
What Drives Metamorphism?

Differential stress (greater in one direction because of mountain
building)
Deformation and development of metamorphic textures
Rocks can react by breaking (brittle) or bending (ductile)
depending on temperature
Chemically active fluids (hydrothermal fluid rich in ions)
Catalyze recrystallization reactions
Can dissolve a mineral from one area and precipitate it in
another
Can change chemical composition of surrounding rock
What Drives Metamorphism?
What Drives Metamorphism
Metamorphism can change the texture of a rock
Low-grade metamorphism makes rocks compact and more dense
High-grade metamorphism causes recrystallization and growth
of visible crystals
Metamorphic Textures
Foliation is the development of a flat arrangement of mineral
grains or structural features

Foliation is characteristic of regional metamorphism
Driven by compressional stress
Causes mineral grains to develop parallel alignment
Includes:
Parallel alignment of micas
Parallel alignment of flattened pebbles
Separation of light and dark minerals
Development of rock cleavage
Nonfoliated rocks occur when deformation is minimal and
parent rock is composed largely of stable minerals
Metamorphic Rocks Textures
Common Metamorphic Rocks

Common foliated metamorphic rocks:
Slate has characteristic rock cleavage
From metamorphism of shale or volcanic ash
Phyllite has larger mineral grains than slate, which give it a
glossy sheen and wavy surface
Schist is formed by regional metamorphism of shale
Gneiss is a banded metamorphic rock that may have intricate
folds
Common nonfoliated metamorphic rocks:
Marble is a coarse crystalline rock
From metamorphism of limestone
Quartzite is very hard because of fused quartz grains
From metamorphosed quartz sandstone

Glacial and AridLandscapesChapter 4 LectureNatalie Bur

Glacial and AridLandscapesChapter 4 LectureNatalie Bur

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