Ch. 23.3 Water Shapes the Land

Objectives:•What is the most important factor influencing the ability of a stream to cause erosion?•What features are formed by surface water erosion?•What features are deposited by running water?•What causes ground water erosion?

Water moves sediment (Erosion) & that changes Earth’s surface features

Deposition = Sediment is laid down in a new location

Stream Erosion – Depends on…(1) Speed of water: Faster streams – carry more

sediment & carry larger sediments = more erosion

(2) Volume: Floods = More water = more erosion(3) Slope: Steeper slope = more erosion.

Features formed by water erosion:

V shaped Valleys

Waterfalls

Meanders

Oxbow Lakeshttp://www.youtube.com/watch?v=ednXhLcwZz0

Features formed by Water Erosion:V shaped Valleys

meanderStreams flow fast down slopes & carry sediments from the stream bed with them – creating a V pattern

V-valleys involve fast moving water in Mt. regions

Yellowstone River has cut a V-shaped valley

Waterfalls form where streams move over rocks that are less resistant to weathering (softer). As this rock erodes faster than surrounding rock a drop is created.

V-shaped valleys can widen into broader river banks and flood plains.

Rivers change shape. Faster moving water on outside bend erodes riverbank (cutbank). Slower moving water on inside bends deposit sediment. Over time this creates BENDS or MEANDERS.

Flooding in a flood plain

Meandering river processes

Features formed by Water Erosion

Meanders & Oxbow Lakes

Meander in Canyonlands N.P., Utah

Green River, NY

Features Formed by Water Deposition• Deltas & Alluvial Fans: Fan-shaped mound of sediments.

Deltas: Rivers dump sediments into large bodies of water (ocean).

Fans: Rivers dump sediment into a valley at the base of a mountain.

Triangle shape of Deltas & Fans

Copper Canyon Alluvial Fan(Death Valley N.P., CA)

Mississippi River Delta

Ground Water Erosion

• Chemical weathering dissolves calcium containing rocks like limestone.

Results:

Caves/Caverns and Sink Holes form

Carlsbad Caverns

Sink hole

Cave Formation: Chemical Weathering (usu. Limestone)

Stalactites: Grow from ceiling (icicles)

Stalagmites: Grow from base & form columns

Water drips into cave. Carbon dioxide enters air, minerals come out of solution to form stalactites & Stalagmites

Stalagtites: Grow from ceiling

Carlsbad Caverns (NM) Limestone slowly dissolving away

Karst Topography (caves and sinkholes in limestone) Ex: Kentucky

Ch. 23.4 Glaciers & Wind

Objectives:

How do glaciers form?

What landscape features are created by glacial erosion & deposition?

What are the effects of wind erosion & deposition

HW QUIZ

1. Describe 2 features/landforms created by glacial erosion.

2. What’s “Moraine” and how is it created?

1. How are dunes created?

Glaciers – Where more snow falls than melts or sublimates

• Continental: Thick ice sheet on huge land mass (Antarctica or Greenland)

• Valley: Occurs in high mountain valley

• (icebergs “calve” off continental marine glaciers)

Glaciers are move slowly

Weight of snow pressing down, makes ice.

Weight of ice layers also melts bottom layer of ice so that glacier can slide.

Glacial Erosion1. Abrasion – boulders trapped under glaciers

gouge and scratch our land and rock surfaces (Glacial striations = claw marks)

2. Plucking – frost wedging that occurs at the base of the glacier breaks up rock.

Glacial Erosion produces…

1. U shaped Valley (Cirques)

2. Horns

3. Glacial Lakes

Glacial Signatures…

5. Till = Glacial sediment of assorted size (Boulders, gravel, sand, pulverized rock dust) formed as glacier erodes surface

6. Moraine – mounds of “poorly sorted” sediment at downhill end of glacier and along sides (Poorly sorted = big clasts/cobbles & fine sediment)

4. “Erratic” Boulder =

deposited by receding glacier

Central Park, NYC• Striations in rock

show the motion of ancient ice sheets.

Poorly Sorted Glacial Till

www.uaf.edu/.../McCall_travelogue_aug03.htm

Glacier Features

Glaciation in our Area

Wind Erosion & Deposition

• Wind erodes land by deflation (wind picks up & carries loose surface material) and abrasion

Wind Deposits: Dunes & Loess

Sand Dunes

Loess – silt deposits from glaciers or deserts