Glaciers and Glaciation

Glaciers and Glaciation What is a Glacier? Formation and Movement Glacial Erosion Erosional Landforms Glacial Deposits Causes of Ice Ages

GEOL131: Glaciers What is a Glacier?

What is a Glacier? Mass of land-based ice In motion downslope GEOL131: Glaciers What is a Glacier? Mass of land-based ice In motion downslope Part of two cycles Hydrologic Rock

What is a Glacier? Four kinds of glacier Alpine (or valley) GEOL131: Glaciers What is a Glacier? Four kinds of glacier Alpine (or valley) Continental (or ice sheet)

What is a Glacier? Four kinds of glacier Ice cap Outlet GEOL131: Glaciers What is a Glacier? Four kinds of glacier Ice cap Outlet

Locations of Modern Glaciers GEOL131: Glaciers Locations of Modern Glaciers Glaciers are shrinking and disappearing worldwide Glacier National Park, Montana: 1910: 150 glaciers 2010: 25 glaciers

Formation and Movement GEOL131: Glaciers Formation and Movement

Formation Accumulation of snow Snow recrystallizes into firn GEOL131: Glaciers: Formation & Movement Formation Accumulation of snow Snow recrystallizes into firn Ice crystals with texture of sand If depth of firn reaches 160 feet, crystals fuse together

Movement Plastic flow Basal sliding GEOL131: Glaciers: Formation & Movement Movement Plastic flow Most movement occurs this way Flow in the solid state under high pressure Basal sliding Small amount of movement Entire ice mass slides along base

Movement Glacier budget GEOL131: Glaciers: Formation & Movement Balance between accumulation and loss of ice

Movement Glacier budget Ice accumulates via Snowfall GEOL131: Glaciers: Formation & Movement Movement Glacier budget Ice accumulates via Snowfall Tributary glaciers Trunk and tributary glaciers, Greenland.

Movement Glacier budget Ice is lost via Melting Calving GEOL131: Glaciers: Formation & Movement Movement Glacier budget Ice is lost via Melting Creates meltwater rivers Calving Creates icebergs Greenland calving event A calving glacier

GEOL131: Glaciers Glacial Erosion

Erosion Mechanisms Plucking Abrasion GEOL131: Glaciers: Glacial Erosion Erosion Mechanisms Plucking Chunks of rock pried loose from glacier’s bed Abrasion Scraping/scouring of underlying rock

GEOL131: Glaciers Erosional Landforms

Glaciated Mountain Valleys GEOL131: Glaciers: Erosional Landforms Glaciated Mountain Valleys Glacial troughs & hanging valleys

Glaciated Mountain Valleys GEOL131: Glaciers: Erosional Landforms Glaciated Mountain Valleys Glacial troughs & hanging valleys

Horns, Cirques, and Aretes GEOL131: Glaciers: Erosional Landforms Horns, Cirques, and Aretes Horn

GEOL131: Glaciers Glacial Deposits

Types of Glacial Sediment GEOL131: Glaciers: Glacial Deposits Types of Glacial Sediment Drift General term for any sediment deposited by a glacier Till Deposited directly from melting ice Unsorted

Terms Stratified drift Deposited by meltwater rivers Well-sorted GEOL131: Glaciers: Glacial Deposits Terms Stratified drift Deposited by meltwater rivers Well-sorted

Moraines Made of till Four kinds: Lateral Medial End (terminal) Ground GEOL131: Glaciers: Glacial Deposits Moraines Made of till Four kinds: Lateral Medial End (terminal) Ground

Lateral and Medial Moraines GEOL131: Glaciers: Glacial Deposits: Moraines Lateral and Medial Moraines Created by valley glaciers

End Moraines Created by all glaciers GEOL131: Glaciers: Glacial Deposits: Moraines End Moraines Created by all glaciers Ridge of till at end of glacier; left behind if ice retreats End moraine

Ground Moraines Created by all glaciers GEOL131: Glaciers: Glacial Deposits: Moraines Ground Moraines Created by all glaciers Layer of till left as glacier retreats Ground moraine

GEOL131: Glaciers: Glacial Deposits: Moraines Moraines in Michigan

Possible Causes of Ice Ages GEOL131: Glaciers Possible Causes of Ice Ages

What is an Ice Age? Extended period of greatly expanded glaciation GEOL131: Glaciers: Causes of Ice Ages What is an Ice Age? Extended period of greatly expanded glaciation Most recent Ice Age: Began about 2 million years ago Ended about 10,000 years ago Glaciers advanced and retreated many times Michigan ice-covered until about 12,000 yrs ago

Maximum extent of ice during last Ice Age GEOL131: Glaciers: Causes of Ice Ages Maximum extent of ice during last Ice Age Accumulation centers Michigan

Possible Causes Plate tectonic movement Variations in Earth’s orbit GEOL131: Glaciers: Causes of Ice Ages Possible Causes Plate tectonic movement Variations in Earth’s orbit Others Changes in atmospheric composition Changes in Earth’s reflectivity Cooling of ocean currents

Plate Tectonic Movement GEOL131: Glaciers: Causes of Ice Ages Plate Tectonic Movement Glaciers can only exist on land To have Ice Age, large land masses must be in polar latitudes

Orbital variations Alter intensity of cold and warm seasons GEOL131: Glaciers: Causes of Ice Ages Orbital variations Alter intensity of cold and warm seasons Three kinds: Precession Obliquity Eccentricity

Orbital variations: Precession GEOL131: Glaciers: Causes of Ice Ages Orbital variations: Precession Wobble of rotational axis 26,000-year cycle

Orbital variations: Obliquity GEOL131: Glaciers: Causes of Ice Ages Orbital variations: Obliquity Tilt angle of rotational axis 41,000-year cycle

Orbital variations: Eccentricity GEOL131: Glaciers: Causes of Ice Ages Orbital variations: Eccentricity Shape of orbit 100,000-year cycle

Other factors: Atmospheric composition GEOL131: Glaciers: Causes of Ice Ages Other factors: Atmospheric composition Greenhouse gases trap heat, keep Earth warm Carbon dioxide, methane, water vapor Lower concentrations = cooler global temps

Other factors: Earth’s reflectivity GEOL131: Glaciers: Causes of Ice Ages Other factors: Earth’s reflectivity Earth’s surface either absorbs solar energy or reflects it Depends on material Lighter-colored material = more reflection = colder temps Glaciers are light-colored, reflective

Other factors: Cooling ocean currents GEOL131: Glaciers: Causes of Ice Ages Other factors: Cooling ocean currents Ocean currents move heat from tropics to higher latitudes If warm currents become colder, average global temp drops

End of Chapter