Base of melting glacier with gradational boundary between dirty ice (top), frozen gravel/till (middle), and unfrozen gravel/till. Subglacial Deposition
Product of Subglacial Deposition of Till: Ground Moraine A ground moraine is body of glacial till deposited beneath a melting glacier
PLUVIAL LAKES Glaciers form because of colder (and locally, wetter) climates. These same conditions decrease evaporation and may restrict plant growth, thus decrease transpiration. As a result, stream runoff may fill natural depressions or basins and form a pluvial lake. One of the largest pluvial lakes to have existed on North America was Pluvial Lake Bonneville. Filled by meltwater from the northern and central Rocky Mountain glaciers, it at one time covered much of the state of Utah. In the 10,000 years since the last glacial maximum, most of Lake Bonneville has dried up and become the much smaller Great Salt Lake
Deposition at Front Margin of a Glacier: Terminal (End) Moraine This is the end moraine left by an ice sheet in Antarctica. Note steep margin of glacier (upper left) retreating after being stable at moraine. "Cold ice" in this polar glacier erodes mostly by plucking from mountains protruding up into the ice, not by sliding and abrading.
Terminal Moraine A terminal moraine is a recessional (end) moraine marking the furthest advance of a glacier. This terminal moraine is in Wisconsin and represents the southern extent of the last glacial advance of the last ice age.
Drainage Patterns Supraglacial drainage (on top of glacier) Englacial drainage (within glacier) Subglacial drainage (at base of glacier)
Supraglacial Water and Drainage Supraglacial water occurs in the form of “slush swamps” and a large Number of streams that drains run-off from the top of the glacier
Ice Tunnels: Subglacial Outflow Passages Sediments are deposited by water within tunnels by subglacial streams
Eskers: Products of Subglacial Stream Deposits Eskers are conspicuous ridges that are typically sinuous in form. This esker transects North Dakota farmland near the former limit of the Wisconsinan ice sheet Harju !
The abrupt change in particle size within the vertical cross-section of this exposure shows evidence of a constantly changing hydrologic flow regime. Discharges capable of transporting cobbles and small boulders were needed to displace the gravel beds near the top and bottom, while the sandy cross-beds in the middle represent lower, more tranquil flows. Esker- Cross Section Showing Internal Structure
Ice-contact stratified drift in kame terrace, near Lake Skaneateles, N.Y. Tilted bedding attributed to deposition of sediment on ice margin, followed by slumping after melting Outwash
Outwash Plain Outwash Plain - a flat or gently sloping surface composed of glacio-fluvial deposits (stratified drift). Copper River Region, Alaska.
RIVER SEDIMENTS Braided river deposit Braided River on Outwash Plain (Fairbanks, Alaska)
Large glacial lake bounded by glacial ice on one side and a beach on the other Interior of beach ridge representing old shoreline of Lake Agassiz LARGE GLACIAL LAKES
Lake Agassiz in total covered an area of 350,000 km 2. Its size and shape changed dramatically over its its 4,000 year history due to runoff volume and position of ice margin At its greatest size (7,500 years ago) the city of Winnipeg lay under 213 metres of water. Today, Lake Winnipeg is a shallow lake averaging only 30 feet in the south. Over time the waters of Lake Agassiz retreated. All that was left is present day Lake Winnipeg. LAKE AGASSIZ
Lake Bonneville represents the highest lake level at about 5090 feet. The lake reached this level about 16,000 years B.P.. A catastrophic event occurred about 15,000 B.P. in which the natural dam at Red Rock Pass gave way and released massive amounts of floodwater into the Snake River Valley. The lake was lowered by 350 feet as a result of this single event. The lake again stabilized about 14,500 years B.P. when the erosion at Red Rock stabilized and the Provo level beacame established. LAKE BONNEVILLE
The horizontal lines etched into the hillside are evidence that a prehistoric lake once filled the valley. The parallel lines represent the ancient shorelines of Glacial Lake Missoula. The highest known shorelines are found at an elevation of 4,200 feet. If the lake existed at this level today, the top of Mt. Jumbo would be an island and the city of Missoula would sit beneath 950 feet of water. LAKE MISSOULA
KETTLE LAKES Tomahawk, Lincoln County, WisconsinKettle Lake, Oak Ridges Moraine, Toronto
FILLED KETTLE LAKE Note sediments lapping onto margin of small lake basin (left)
VARVES (FOUND IN MARINE AND LACUSTRINE SEDIMENTS) Varve = “Turn” Couplets of sedimentary layers Indicating cyclic deposition. In glacial environments, can be used to indicate summer-winter cycles Thick, light = summer Thin, dark = winter
Ice calving off Antarctica Ice Sheet 90% below the surface; compared to size of a ship Ice Calving
Iceberg Keel Marks View between Lake Manitoba and Winnipeg; May 20, 1990: The large squares are land sections (1500 by 1500 m). The criss-crossing lineations are iceberg keel marks 2 to 4 km In length. Note that several of these are 2 to 4 km in length.
Drumlins (Formed Due To Glacial Advance Over Pre-Existing Till) Classic streamlined profile of a drumlin. Alberta, Canada Swarm of drumlins, Wisconsin
Kame Kames are mounds or hills created when drift fills a hole in a glacier. When the glacier recedes the mound is left behind. Happy Valley Nunatarssuaq region, Greenland
Ice Wedge Polygons Muir, Ontario (close to Woodstock). These polygons were likely formed due to frost wedging during a short-lived periglacial episode following ice retreat of the Wisconsinin ice sheet (ca. 15,000 to 13,000 years before present). Other Glaciation-Related Features
Good Luck on your Review Sheets and Test on Chapter 17
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