Glaciers and Glaciation Chapter 21

Why do we care 1. Erosion 2. Climate change

Glacier erosion and transport: who cares? 1. topography, sediments, rock cycle

Glacial Valley with LAKES

Glacier erosion and transport: who cares? 2. records of climate change

Glacier erosion and transport: who cares? 3. Sea level change

What causes the snow that falls on a glacier to become ice? A) changing humidities B) colder temperatures C) pressure from the overlying snow D) heat from the sun

How snow turns to ice

AB

OU

T 50

MET

ERS

(160

feet

)

Glaciers, Glaciation and Landforms

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

• Types of glaciers • Valley (alpine) glaciers

– Exist in mountainous areas – Flows down a valley from accumulation

center at head

Valley Glacier Flows off Ice Sheet

Valley glacier off ice cap

• Types of glaciers • continental glaciers or ice caps

– Cover huge areas: Antarctica, greenland – Flows from accumulation center, but not

down a valley

The dry valleys

Alpine or valley glaciers

Greenland

Continental glaciers or ice caps

500 km

Movement of glacial ice (“flow”)

1. Plastic flow » Occurs within the ice » Under pressure, ice behaves as a plastic

material

2. Basal slip » Entire ice mass slipping along the ground » Most glaciers move this way by this

process

Glaciers move by basal sliding and internal flow

Movement of glacial ice

• Rates of glacial movement • Rates of up to several meters per day • Some glaciers exhibit extremely rapid

movements called surges

Record of a surging glacier

Part II. Glacier mass balance

Accumulation zone: snow > melt Ablation zone: melt > snow

Glacier mass balance

Change in ice volume = input – output Change in ice volume = snow – melt

What will happen if??? Change in ice volume = snow – melt If snow > melt, ice volume increases A) Terminus retreats B) Terminus advances

When does terminus ADVANCE

Change in ice volume = snow – melt If snow > melt, ice volume increases COLDER temperature or MORE PRECIPITATION

Sierra Nevada, California

Simulated ice thickness and distribution

When does terminus RETREAT

Change in ice volume = snow – melt If snow < melt, ice volume decreases WARMER temperature or LESS PRECIPITATION

• Budget of a glacier

• Balance between accumulation and loss – If accumulation exceeds loss the glacial front

advances – Of loss exceeds accumulation, front retreats

Why did glacier front retreat?

• A) colder temperature • B) warmer temperature • C) more precipitation • D) A and C

Basic Idea: 1. Glaciers advance: when temperature lower or more

precipitation 2. Glaciers retreat: when temperature higher or less

precipitation

When did this happen? How many times did this happen? Why did it happen? could it happen again?

Glacial deposition 1. Glacial ice flows towards terminus 2. Sediment deposited at terminus 3. Largest deposits when terminal position steady

TERMINUS

Terminal moraine

Moraines - Eastern Sierra Nevada, California

Glacier erosion and transport glaciers are world champions of erosion and transport

How do glaciers erode? Glaciers move by: 1. basal sliding 2. internal flow

3 main processes of glacial erosion

1. Plucking – lifting of rocks from “bed” 2. Abrasion – sliding over bed smoothes the surface

– Sediment within the ice is critical

3. Mass movements onto ice surface – Rock fall

PLUCKING

Glacial Polish

ABRASION

Glacial Striations

ABRASION

Mass movements

Glacial erosion produces

spectacular topography

Matterhorn in the Swiss Alps

Sharp Peaks, Horns and Cirques

Cirque

Glacial Valley with LAKES

Fjord - a drowned glacial valley

Hanging Valley - Yosemite Natl Park

Glacier transport lots of sediment in the ice and at the surface a wide range of grain sizes

Moraines (lateral or medial)

Glacial transport Boulders and other sediment

Where do glaciers deposit material they carry?

TERMINUS

Glacial deposition 1. Glacial ice flows towards terminus 2. Sediment deposited at terminus 3. Largest deposits when terminal position steady

TERMINUS

Terminal moraine

Lateral Moraines - Eastern Sierra Nevada, California

Terminal moraines from continental glaciers

Glacial deposits are typically unstratified and unsorted

Unsorted Glacial Till

Glacial deposits can be sorted and stratified: liquid water sorts material

Glacial depositional features

Drumlins – Occur in clusters called drumlin fields

Glaciers and climate change Widespread evidence that size of glaciers

change through time Important because it tells us: 1. Climate varies 2. The impacts of climate change are

DRAMATIC (big sea level changes)

1. Terrestrial records 2. Glacier mass balance reviewed 3. Oceanic records and orbital forcing

1. Terrestrial records of glaciations Two types of glaciers

Alpine or valley glaciers

Greenland

Continental glaciers or ice caps

500 km

Shelton photo Field trip up a valley Another moraine

Trip up a valley Near top of valley Small, sharp moraine No vegetation

Cirque in top of valley may have a small glacier

Field Trip II. Massachusetts; Glacial erratic:

1. A big rock 2. different rock type than bedrock

Glacial deposits stretching for 100’s km 1. Poorly sorted, no stratification 2. Sorted with bedding

Large portion of N. America covered by continental glaciers

Terminal moraines from continental glaciers

Glacial deposits are typically unstratified and unsorted

Unsorted Glacial Till

Basic Idea: 1. Valley glaciers larger in the past 2. Large portions of northern continents covered by ICE SHEETS

When did this happen? How many times did this happen? Why did it happen? could it happen again?

The little ice age: historical records

Why did glacier front retreat?

• A) colder temperature • B) warmer temperature • C) more precipitation • D) less precipitation • E) B & D

Little Ice Age 1800’s

What about the other glaciations?

Which order is correct, from oldest to youngest

a) tahoe, tioga I, tioga II b) tioga I, tioga II, tahoe c) Tioga II, tioga I, tahoe d) None of the above

What about the other glaciations?

3-4 distinct moraines; Relative dating cross-cutting

relationships

Soil development

Why did glaciers advance and retreat?

Basic Idea: 1. Glaciers advanced: when temperature lower or more

precipitation 2. Glaciers retreated: when temperature higher or less

precipitation

When did this happen? How many times did this happen? Why did it happen? could it happen again?

The number of protons determines the element

The neutrons of a given element

may vary ISOTOPE: variations of the same

element, with different # of neutrons, and so different atomic weight

Isotope

Part III. Oceanic records

Isotope of Oxygen

Oxygen 16 Oxygen 17 Oxygen 18

Isotopes of H2O

H2O16 most common

Marine organisms make skeletons out of CaCO3

A diatom: SiO2 skeleton

H2O18 accounts for 1 in 1000 water molecules

Ratio of O16/O18 of sea water

ICE SHEET

Water stored in ice sheets has relatively few H2O18 molecules

Record of ice volume from ocean sediments Lots of ice: H2O18 relatively high in oceans Little ice: H2O18 relatively low in oceans

WOW 1. Many, many ice ages !!!!!!! 2. Interval varies; timescales of 10,000 to 100,000 years

Maximum extent of ice during the last Ice Age

Last warming

trend leads to

rise in sea level

Present level is

very high!

Ice sheet reconstructions 21 ka 14 ka 12 ka

10 ka 8 ka 0 ka

Peltier (1994)

Why do we have glaciers advance and retreated over and over again?

Hypothesis: linked to variations in Earth’s orbit and variations in solar input 1. eccentricity 2. precession 3. tilt

2. TILT

3. Precession

Comparison of orbital variations with isotope records

• What if the ice on Earth melted? • ~ 2 percent of the world’s water is in glaciers • Antarctic ice sheet

– 80% of world’s ice – 65% of Earth’s fresh water – Covers 1.5 times area of the United States – If melted, sea level would rise 60 to 70 meters – (wave goodbye to Florida, New York, coastal cities)