Lab 13: Glaciers and Periglacial Landscapes

cirques, tarns

(French for circus) bowl-shaped features found along mountain peaks that were carved out by alpine glaciers, lakes that form in cirques are called ______

aretes

(french for ridge), are very thin rocky ridges that formed between two alpine glaciers

firn

a material that is formed from the snow on a glacier falling and being compressed; similar to ice, but its density averages around .9 g/cm3, lower than that of ice; granular snow on the upper part of a glacier, where it has not yet been compressed into ice

horn

a three-sided mountain peak that has been eroded by alpine glaciers

eastern third, falls

about a million years ago, the ______ ______ of Nebraska was covered by a glacier from Canada; during glacial periods sea level _____ because instead of running off, more water is held in glaciers rather than running off into the oceans

Canada, Pleistocene, cooler temperatures

continental glaciers advanced from _______ into the United States at least 10 times in the past 2 million years; period of time is called the ________ (last Ice Age); these periods of large scale global glaciations are caused by much ______ ______ than normal

drumlins

distinctive, hills that form in glaciated landscapes; useful for telling the direction of glacial flow because the steep side of the _____ formed toward the ice

kettle lakes

formed when glacier ice is buried in sediment; when ice melts after glacial period, the depression that is left commonly holds water making the lake; Great Lakes, and lakes in Minnesota, Wisconsin, and Michigan are these type, formed during last ice age

zone of accumulation, accumulating snowfall, white

found at the head of the glacier's movement; area where the glacier gains mass by _______ _______; snow that falls in this region generally does not melt and eventually will turn into firn and then glacial ice, this zone commonly appears ______, on glaciers as it is the color of snow

jagged peaks, wide, U-shaped, lakes

glaciated mountains (alpine glaciers) have very ______ ____, _____ ___-______ river valleys and _____ are common; e.g. European Alps and other mountainous areas of the mid-continent; erosive features and depositional features

temperature, precipitation

glacier growth is dependent on two primary factors:

tens of hundreds of meters per year

glacier movement is on the order of ____ ___ ______ __ _____ __ _____

only form on land, open water

glaciers ______ _____ ____ _____; they cannot form over _____ ______ because the snow that falls on _____ ______ melts

always moving forward, move forward,

glaciers are _____ _______ _____; even when glacier's snout or front end is retreating, the ice within the glacier continues to ______ _____, as it is being pushed by the weight of the ice behind it

aretes, cirques, horns

glaciers are effective at eroding rock in alpine regions causing common erosive features like _____, _____, and ______

downhill

glaciers move _______ under the influence of gravity; in areas where glaciers form snow accumulates faster than it melts, so in general temperatures are cold and summers are not warm enough to melt much of the snow that falls

glacial erratics

large boulders that have been moved by glaciers; typically rock types that are not commonly found in the area that they were deposited in; e.g. pink boulders in Lincoln that were moved from glaciers in Sioux Falls, SD around 1 million years ago

glaciers

move from the repeated accumulation of snowfall over hundreds or thousands of years

moraines

piles of sediment that have been formed at the front of, or compressed below the advancing glacier, most composed of till; terminal, recessional, lateral, and medial

.1, .6, .9, density

pressure to create glacier is supplied by the mass of ever-accumulating snow; falling snow has density of ____ g/cm3, as snow is buried it turns into firn which as _____ g/cm3 density, further compression from more overlying firn and snow acuses firn to turn into glacier ice, which has density average of ____ g/cm3; as this transition goes on, ____ ______ are being forced out of ice acting to increase ______ of the glacier

till

rock and sediment that has been moved by the glacier and deposited after it has melted is called _____

zone of ablation, high summer, grey, brown

the area where the glacier is experiencing net loss of material through melting of snow and ice; in general, relatively _____ ______ temperatures cause the greater degree of melting; surface in this area appears ____ or _____ in color because the snow and ice have melted, exposing the sediment and rock that were carried in the glacier

mass of balance

the difference between snow gain (accumulation) and snow and ice loss (ablation; glaciers advance when gains outweigh losses resulting in a ______ mass balance, and glaciers retreat when the mass balance is ________; even when the front of the glacier is retreating the glacier is still moving forward

alpine glacier

the type of glacier that forms in mountain valleys and form at high elevations where persistent cold conditions limit the amount of annual snow melt; today found from the equator to the polar regions

continental galciers

the type of glaciers that form over large areas such as continents; today they cover Antarctica and Greenland, but in the recent geologic past they have covered much of the northern portions of Europe, Asia, and North America

ice, pressure, re-crystallization

to create a glacier, the snow that falls has to be turned into ____, a process that requires _____ and __________ of the snow