Gifts of the Glaciers

Transcription

1 Gifts of the Glaciers Gifts of the Glaciers Moving ice of glacier was responsible for water, landforms, and soil characteristics and patterns of today Sculpturing of bedrock materials Glacial Landforms Erosion of bedrock Deposition of glacial drift Glacial Landforms Glacial landforms dominate the Great Lakes region Northeastern Illinois Northwest Indiana Most of WI, MI, MN, and Ontario Glacial Landforms Effects of moving ice: Leveled off the existing hills Filled in valleys Blocked the drainage of the rivers Gouged out major basins (ex: GLB) Processes involved: grinding, erosion, leveling, and depositing. Glacial Erosion Glaciers perform, in many ways, like an excavator. Although they can push weak material, like gravel, like a bulldozer blade, they are far more likely to lift material out of place, like a backhoe, or scratch it in place, like a ripper. And, like a bulldozer, glaciers are poor at eroding rock unless it is already weakened. Rock Failure: The first step in glacial erosion is rock failure. Water, ice causes cracks in rocks

2 Glacial Erosion Plucking Two main types of glacial erosion Plucking (analagous to a backhoe). Abrasion Plucked debris in basal ice grinds into the bedrock, just like sandpaper across wood Glacial Erosion Glacial / Fluvial Processes: At the bed of warm-based glaciers, water is present in it s fluid state. This water flows underneath the glacier and assists erosion by removing erosional products, especially silt. When water collects into subglacial channels, it can be sufficiently powerful to erode by itself Abrasion Subglacial view of basal debris Glacial Outwash Stream

3 Glacial Landforms Glacial Outwash Stream Material deposited by glaciers is called drift Till is deposited directly from glacier Outwash is deposited by meltwater In summer, meltwater carried along rock flour sediments In winter these were blown by wind Left thick beds of loess downwind from major river valleys Glacial Drift Till that has melted out from the dark striped basal ice layer. Outwash plain and braided streams Outwash plain Glacial Till North Shore L. Superior

4 Outwash sediments Till exposure (dark tan) located above outwash sediments (light tan) Glacial Grooves on Kelleys Island, Ohio Glacial Striations on Canadian Shield Bedrock Large Glacial Erratic

5 Large Glacial Erratic Glacial Landforms Rock, gravel, sand, and silt left behind by melting glaciers formed mounds, ridges, and thick windblown deposits. Moraines mark re-advances of glacier and when glacier stalled as it retreated Accumulated drift is pushed into higher mounds by ice Glacial Landforms End Moraines During periods when the rate of ice advance nearly equaled that of melting, huge mounds of sand and gravel piled up in curved ridges along the glacier's edge.

6 End Moraine Ground Moraine End Moraines Valparaiso morainic system Illinois Moraines Marseilles morainic system The end moraines from the Wisconsin glaciation can be seen in Northeastern Illinois. Glacial Landforms Ground Moraines - Ground moraines are formed as till is deposited directly beneath a glacier; between the ice and the underlying rock. Ground moraines are located behind end moraines. Form gently rolling to flat countryside. End Moraine Ground Moraine

7 Ground Moraine Ground Moraine Moraines Ground Moraine with Kettles End moraines - western suburbs of Chicago Form at melting end of glacier as till piles up Belts of rolling or rugged hills with intervening swales, swamps and lakes Ground moraines - DeKalb county Form as ice front retreats and leaves a flatter deposit Gently undulating lands Moraines End Moraine Recessional moraines are formed when the ice stands still and melts. Ground Moraine

8 Moraines Recessional Moraines Push Moraine - A ridge or pile of unstratified glacial sediment that is formed in front of the ice margin by the terminus of an advancing glacier, bulldozing sediment in its path. Kettles Ice Block/Kettle Hole Lakes Kettles Depressions formed when ice broke into chunks that became buried in sediment. When the ice block melted, it left a depression, which sometimes filled with water to form kettle lakes. Kettle lakes are common in northern and central Illinois. Kettle Hole Lakes These are usually deep lakes Many still have water Steep sides Most Great Lakes region lakes are kettle hole lakes Minnesota = Land of 10,000 Lakes Volo Bog formed in a kettle Volo Bog

9 Iceland Kettle forming with ice block still in place. Kettle within Morainal Ridges Outwash Plains Outwash Plains At the glacial front, water flowing from underneath the ice formed level plains of fine sediment. Outwash plain and braided streams Outwash plain

10 Drumlins Drumlins are low, smoothly rounded hill of compact glacial till, built under the margin of the ice and shaped by its flow Sculpted by active ice during a re-advance over an old till plain Arranged more or less parallel Separated from each other by poorly drained troughs or swales Drumlins The Antrim-Charlevoix drumlin field is one of the largest in the midwest.

11 Drumlins at Kejimkujik Provincial Park, Nova Scotia, CA Drumlin Fields along coast of Michigan Drumlins near Auburn, New York, looking southeast. Owasco Lake is in the upper right Eskers Eskers are long narrow hills that look like abandoned railway embankments Long, winding ridges of sand and gravel formed in waterways under the glaciers. Long narrow winding ridges of stratified gravel, sand and silt Formed under stagnant rather than moving ice Form low, sinuous hills that can stretch for miles and often resemble snakes when seen from the air Eskers

12 Esker Esker Kames Esker cross-section. Eskers are often mined for gravel Kames - Smaller mounds of sand and gravel formed where sediment filled cracks in the ice. Stratified hills of cobble, gravel, sand, and silt Formed when meltwater plunges into crevasses/ moulins on the ice surface or at the ice front and deposits its load of sediment Conical (more or less) sometimes ridgelike in shape Series of kames at Glacial Park in McHenry Co. Kames A moulin (glacier mill) on a modern glacier

13 Prairie Kame in Kane County Camelback Kame at Glacial Park, McHenry Co. Illinois Glacial Soils Moulin Kame in the Kettle Moraine, 4 miles northeast of Dundee, WI. Conner Hill, looking southwest Regional soils are also the result of glacial deposits Nonglaciated areas Driftless area of SW WI Limestone bedrock exposure areas of sw Cook and western Will counties Ice picks up rocks and other debris Ice grinds rock bedrock into fine silty deposits called rock flour or loess (luss) Loess Deposits Loess Deposits During the cold seasons, the flow of glacial meltwater slowed. Fine silt that had been deposited on the outwash plain and along river channels leading from the glacier was exposed and dried out. Winds blew the dust to surrounding areas where it slowly grew into thick silt deposits called loess. Vertical faces of loess, sometimes over 30 meters (about 100 ft.) high, can be seen along the Mississippi and Illinois River valleys. Loess bluff near Edwardsville, IL.

14 Glacial lake plains Illinois loess deposits Sediments of glacial and proglacial lakes, also river sediments that flowed into lakes May have sand dunes far from any modern water source Beach ridges Visible at Indiana and Illinois Dunes Often have special soils Marl (calcium carbonate: mined for cement and fertilizer) Special crops farmed on these soils Navy beans Sugar beets Soy beans Glacial Lake Plain Bounded by Moraine