Glaciers and Glaciation • Glacier mass of of ice ice composed composed of of recrystallized recrystallized >> aa mass compacted snow snow that thatflows flows under under its its own own compacted weight on on land. land. weight • Presently glaciers.
Download ReportTranscript Glaciers and Glaciation • Glacier mass of of ice ice composed composed of of recrystallized recrystallized >> aa mass compacted snow snow that thatflows flows under under its its own own compacted weight on on land. land. weight • Presently glaciers.
Glaciers and Glaciation • Glacier mass of of ice ice composed composed of of recrystallized recrystallized >> aa mass compacted snow snow that thatflows flows under under its its own own compacted weight on on land. land. weight • Presently glaciers cover11//10 of the 10 Earth's surface. • Glaciers occur in Greenland and Antarctica and in higher mountain ranges. GlaciersImportant in understanding global scale climate change Related to all 5 of the Earth’s systems Exosphere- changes in the amount of sunlight cause glaciations Hydrosphere- glacial ice is frozen water, part of the hydrosphere Geosphere- Glacial ice flows over and modifies land Atmosphere- alteration of global atmospheric patterns contributes to glacial ice formation Biosphere- ice displaces animals and plants Importance • Glacial times represent significant time periods in Earth's history Proterozoic, Pennsylvanian, Pleistocene • Represent major climatic departures from the modern on a Global Scale • Cyclic in Nature • Man's Influence??? • Glacial Ice contains records of past atmospheric changes Origin of ice • Snowflakes are melted & deformed by the pressure of overlying snow, becoming granular snow, then firn, and finally interlocking crystals of glacial ice. Descriptive classification of Glaciers • Valley (or Alpine) Glaciers are confined to mountain valleys. > may eventually cover the entire mountain range becoming a mountain ice sheet > may also spill onto low flatlands becoming Piedmont glaciers • Continental (or Ice Sheets) > cover vast areas of more than 50,000 km22 . Today, continental glaciers are only found in Greenland and Antarctica. > Not so in the geological past Response of a Glacier to Changes in Glacial Budget If accumulation = ablation, then no advance or retreat, but continues to flow If accumulation > ablation, then glacier advances while flowing If accumulation < ablation, then glacier retreats, but continues to flow Effects of Glaciers • Fills in the low spots valleys and and basins basins get get filled filled in in w/ w/ sediment sediment >> valleys • Knocks down the high spots mountains and and hills hills get get eroded eroded >> mountains • Reroutes the drainages valley filling filling may may block block streams, streams, causing causing >> valley new paths paths to to be be taken taken new • Deposits accumulate in specific places related to flow and meltwater characteristics • James Lobe and Glacial Lake Agassiz Erosional Processes ･ Important erosional processes associated with glaciers include plucking, abrasion, and bulldozing. ･ Plucking and abrasion are most common > can form a landform called a roche moutonnee Erosional features Roche Moutonnée Erosional features •Hanging Valley •Horn •Arete •Cirque •U-shaped trough •Col •Truncated Spurs Glacial Deposits • glacial drift-A general term referringtotosediment sedimentformed formedby byany refering Any glacial action. glacial action. • Till (Diamicton) poorly sorted, unlayered material directly deposited by a glacier; ice contact deposited by a glacier; • Stratified drift (Outwash)sorted, layered sediment usually deposited by meltwater streams. Proglacial or ice contact Depositional featuresglacial erratic A glacial erratic Yellowstone Park 6 ft Sediments- Glacial Till exposed in Iowa Depositional features- moraines Moraine formation- made of Till, deposited by ice Depositional features- moraines Moraine formation- made of Till, deposited by ice Depositional features- moraines Moraine formation- made of Till, deposited by ice Lateral Lateral moraines moraines Medial Medial moraines moraines ･ Lateral and Medial Moraines are sediment eroded from the valley sides and deposited by a glacier. They often appear as dark stripes in a glacier. Depositional features- distribution of moraines Depositional features- Kames, eskers, kettle lakes, drumlins, outwash plain (sandur) Depositional features- Kames, eskers, kettle lakes, drumlins, outwash plain (sandur) Outwash with kettles moraine Kame terrace Outwash Kettle lakes Outwash Plain with eskers and a braided stream Pleistocene Glaciation Glaciations • The Pleistocene "ice age" began ~1.96 million years ago • Several glacial and interglacial Episodes have occurred. episodes. Glacial -- aa period period of of ice ice advance, advance, generally generally >> Glacial interpreted as as aa globally globally cool cool period. period. interpreted Interglacial -- aa period period of of ice ice retreat, retreat, generally generally >> Interglacial interpreted as as aa globally globally warm warm period. period. interpreted We are in an interglacial period right now MilankovitchOrbital OrbitalTheory Theory Milankovich • Proposed to account for the cyclical nature of Glaciations. • Astronomer & Mathematician Milutin Milankovitchattributed attributedthe theglaciation glaciationto to Milankovich variation in three parameters of the Earth's orbit. Obliquity- not shown eccentricity precession warm warm cold cold 1 3 4 5 Erie Lobe