Chapter 14. Glacial and periglacial landforms.

Climate change involves global warming but also cooling. The great lakes were created by the movement of glaciers towards the equator south and also as a result of the glaciers retreating back north. 11.000 years ago, the ice age startedthe ice fron was north of the great lakes, 6500 years ago the ice sheets of these glaciers were completely gone.

1.-Types of Glaciers: Glaciers are part of the cryosphere.&0% of earth’s fresh water is stored in the cryosphere in the form of glaciers. Glaciers can form in tropical and equatorial zones if the elevation is high enough to keep average annual temp, below freezing

Cryosphere: The portion of the hydrosphere in which water is stored as ice.

Glacier: A natural accumulation of land ice affected by present or past motion. Glaciers are the result of a large pressure created at the bottom of a large pile of snow. It is compacting toward the bottom and pressuring, the snow accumulates and end up as a glacier. Glaciers have to do with the motion of the glacier from one place to another

Types of glaciers: Alpine glaciers and Ice sheets or Contint’l glaciers.

ALPINE GLACIERS: Is a glacier formed at high elevation, typically flowing down steep mountain slopes and filling valleys below. It is on top of the mountain, aside or along the mountain, need sufficient snowfall and temp. cold enough to maintain year round snow cover.. Ex. Himalayan glaciers feeed the rivers of china, SW Asia and India. The recent decline of this glaciers is a serious thread for these regions.

2.-Types of Alpine glaciers: Alpine glaciers go through different stages of a process. There are 4 types:

a- Cirque Glacier: Is the first stage of a process. Alpine glaciers originate from a snowfield that has collected in a bowl-shaped depression called CIRQUE, where snow is compressed and highly pressurized and contained within the basin. If enough snow accumulates the pressure is too much and the snow slides down the mountain, we’ll see slower type of carving, then comes more snow to form valley glaciers

b.- Valley Glacier: flow down steep sided valleys once carved by streams. Ex. St. Elias Alaska. Most alpine glaciers float out of these basins to become VALLEY GLACIERS which occupy sloping stream valleys between steep rock walls.

c.- Piedmont Glacier: when a valley glacier flows out onto a surrounding plain at the base of the mountain, it forms a piedmont glacier. Ex. Turnstone glacier, canada

d.- ICEBERGS: When a valley glacier terminates in sea water at the base of the mountain, the water will erode the glacier, melting at the same time, and bringing more water, the glacier will float in water, as a tidewater glacier, blocks of ice break off to form icebergs. It is a glacier that end in the water filled by an arm of the sea.

3.- ASSOCIATED WITH ALPINE GLACIERS ARE: ICE CAPS and ICE FIELDS

a.- ICE CAPS: ICE MASSES OF MOUNTAIN TOPS WITH DISTINCTIVES DOMES. Ice caps are continuous masses that cover mountain tops with distinctive domes.

b.- ICE FIELDS: interconnected valley glaciers along the mountain.

ICE SHEET ORCONTINENTAL GLACIER: A large, thick plate of glacial ice that moves outward in all directions. Artic and polar regions. It is an extensive type of ice mass., they are not associated with mountains. At some locations, ice sheets extend long tongues to reach the sea, known as outlet glaciers. In other locations, glaciers meet the sea to form great plates of floating glacial ice, called ice shelves that can break up and drift away floating over water, not over land, the broken ice creates navigational hazards.

1.Which location is not covered with an ice sheet? North Pole, which lies in the middle of arctic ocean and because ice here occurs only as floating sea ice. Today the only remaining ice sheets are Greenland and Antarctica.99% of the world’s ice is in Greenland and Antarctica. Antarctica is the largest and thicker ice sheet in the world.It covers 5 millions miles, 13.000ft of ice and 3200 ft or 2 miles thick. It is thicker than Greenland ice sheet. 78% of the land in Greenland is covered by ice and occupies 670.0000 milles with the form of a dome. Ex. Wilkings ice shelf in Antarctica, is melting impacting the sea level around the world.

2.ICEBERGS: bodies of land ice that have broken free from glaciers that terminate in the ocean.

3 .Except with the colder glaciers--------is the primary mechanism of glacial motion.

Glacial Processes—Formation of Glaciers

4.- Formation of glaciers:

Glacier form as snow accumulates from year to year. When the snow fall of winter exceeds the loss of snow in the summer due to evaporation and melting, a new layer of snow is added to the surface of the glacier. FIRN: surface snow melts and refreezes on warm days, and cold nights, compacting the snow ant turning into a granular ice called FIRN. This intermediate ice is compressed during 25 to 1000 years, into hard crystalline glacial ice by the weight of the layers above it.

a.- THE ZONE OF ACUMULATION: identifies the part of the glacier where snow is accumulating. Snow exceeds evaporation and melting in the zone of accumulation, where new glacial ice is formed. Precipitation rates temp. and volume of snow layers dictate the rate of glacial formation. When the ice mass becomes so thick that it begins to move under the force of gravity, it becomes an ACTIVE GLACIER. Flowing downhill the glacier find less snow and warmer temp.

B.- Zone of ablation: At lower elevation, Evaporation and melting increase, more ice is lost than is formed. This part of the glacier is the zone of ablation: the zone at the bottom of the mountain where glaciers shrinks because is warmer. Between these 2 zones is the

C.-EQUILIBRIUM LINE: where the rate of snow accumulation balances the rate of evaporation and melting. The equilibrium line marks the location where accumulation and ablation are about equal. Glaciers growing and shrinking.

GLACIER: is an open system that has a dynamic balance between the input of accumulated snow and the output of melting or evaporating snow.

5.-MASS BALANCE: is the glaciers input and output. Mass balance changes each year as a result of the annual temp. and the amount of snowfall. If more snow falls than melt each year, the glacier gets larger. If the mass balance remains positive for some years, the glacier grows in bulk, and its end point, called TERMINUS, move forward. Terminus is the lower end of the glacier, if glacier grows the terminus will move forward the mountain. But, if the mass balance remains negative, the glacier shrinks. Ex. Mc. Call Glacier in Arctic. has the longest amount of details recorded by scientist (record how much has retreated).

6.-MOVEMENT OF GLACIERS:

A GLACIER IS ALWAYS FLOWING OUTWARD AND FORWARD, EVEN IF THE FRONT IS RETREATING. The motion is few cms./day. Most glacier movement occurs by slippage between the bottom and sides of the glacier. In all except the coldest glaciers, high pressure at the base couple with the slow flow of geothermal heat, and heat caused by friction, creates a layer of liquid water that allows him to slide downhill in a process called BASAL SLIDING.

BASAL SLIDING : except on coldest glaciers, basal sliding is the primary mechanism of glacial motion, where layes of water under the glacier along which glacier slides. Due to more heat at the bottom of the glacier, more pressure that increase melting, layers of water forming beneath. As it moves, it creates more friction, more heat and water to slide.

CREVASSE: breaks in the brittle surface layer. The surface of the glacier bears less weight and is more brittle, as the glacier moves over the cliff, the brittle surface layer may crack due to tension and form CREVASSE that are deep fissures in the ice resulting from stresses in the surface and form perpendicular to the direction that the glacier flows.

7.- GLACIAL EROSION AND DEPOSITION

GLACIAL DRIFT: A general term for all the varieties and forms of rock debris deposited by moving ice sheets. Are different types of deposits of materials that glacier leave behind. As glaciers move down the mountain they deposit rock and boulders. They can break bedrock and carved part of It., rocks are going to be polished.

STRATIFIED DRIFT: consist of layers of sorted and stratified clays, silts and sand. Or gravels or layers of fine grains sediment that the glacier moves down the mountain, glacier captures silt and clay forming different layers of sediments as the glacier retreats.

TILLS: is an unstratified mixture of rock fragments, ranking in the size from clay to boulders, that is deposited directly from the ice without water transport. Ex. Ohio, Nebraska

MORAINE: The accumulation of rock debris carried by an alpine glacier of an ice sheet and deposited to become a depositional landform.

GLACIAL ABRASION: produces grooved and polished bedrock surfaces that mark the path of an advancing glacial ice.

8.-GLACIATION: A single episode or time period in which ice sheets and alpine glaciers formed, spread and disappeared. Massive sheets of glacial ice covering Southern North America and Eurasia more than 12 times during 2.5 million years.