Glaciers and the Great Ice Ages

Pleistocene Epoch: the Great Ice Ages 2.0 Ma to 10,000 years ago Four (or more) distinct episodes expansion and melting of ice sheets (continental glaciers)

Why did the climate change so drastically and repeatedly? Climate change and variations in Earth’s orbit Eccentricity: elliptical to nearly circular cycles Obliquity: cyclic changes in tilt of axis Precession: cyclic change in”wobble” of the axis Variations affect amount and distribution of solar energy received by Earth

How does a glacier form? Cold climate is necessary Annual snow accumulation is greater than annual rate of melting Snow builds up over time Snow recrystallizes to ice

Glacial Flow Ice begins to flow (plastic deformation) under the influence of gravity Glacier = mass of flowing ice

Glacial Flow Glacial Flow is constant Some parts of glacier are melting Rate of accumulation vs. rate of melting determines if glacier will advance or if end of glacier will melt back (glaciers never flow backwards)

Glaciers and Landscapes Flowing ice picks up sediment, soil, etc. Breaks loose pieces of bedrock Modifies landscape by erosion and deposition

Erosion by Glaciers Striations: “scratch”marks made as ice drags rocks across bedrock

Erosion by Glaciers Modifies “V” shaped river valleys to a “U” shape

Deposition by Glaciers Erratics – pieces of “exotic” rock left by glacier Till – unsorted, unstratified sediments dumped by ice Outwash – sorted and stratified sand and gravel deposited by meltwater

Deposition by glaciers Lacustrine sediments Lakes form between melting edge of ice and obstructions (often deposits of till) Fine silt and clay settle in calm water Clay may be used in pottery and brick making If lakes drain or fill with sediment: bogs and swamps – ecologically important wetlands Water-logged lacustrine sediments may cause tilting and sinking of buildings constructed on them

Glaciers and Landforms Characteristic landforms

New York’s Glacial Landscape Shaped by Erosion and Deposition

Glaciers and New York’s Landscape Great Lakes – Erie and Ontario Glacially widened and deepened E-W stream valleys Finger Lakes Glacially deepened N-S stream valleys Mohawk Valley – “misfit” stream Glacially widened and deepened E-W stream valley Glacial Lake Albany – drained when ice left Hudson Valley

Glaciers and New York’s Landscape Susquehanna Valley modified to U shape Dammed by till at Wells Bridge (near Otego) Dam broke and lake drained

Glaciers and New York’s Landscape Hudson Valley – a fjord Glacially deepened N-S stream valley Flooded when sea level rose Salt water as far north as Poughkeepsie Tides affect river level as far north as Troy Ocean freighters can sail up to Albany – an inland seaport

Kensett’s Hudson - Fjord

Palisades (igneous rock) along the Hudson Fjord

Hudson Fjord, Long Island Sound, Moraines and Outwash of Long Island

Glaciers and New York’s Landscape Long Island Two terminal moraines Outwash plain Long Island Sound - Glacially widened stream valley flooded by rising sea level

Other Glacial Features Outwash channels – Niagara River “Hanging” valleys and waterfalls – very prominent in the Finger Lakes Kettle lakes Drumlins

Church’s Niagara Falls – Outwash Channel

Glaciers and New York’s Economy Thick, fertile soils developed on till and outwash – foundation of agriculture in state Microclimate associated with Lakes Water moderates climate Warmer in winter, cooler in summer Ideal for growing grapes/producing wine Aquifers – especially in outwash Sand and gravel for construction