glacial geology of northeast pennsylvania. how do we know they were here? geologic forensics…look...
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Glacial Geologyof
Northeast Pennsylvania
How do we know they were here?
Geologic forensics…look for the evidence…
…and an 800 pound gorilla leaves a lot of evidence!
Glacial grooves and striations
Chatter marks
Characteristic landforms, e.g., horns
Kettle lakes on an outwash plain
Does this look familiar?
The world famous Archbald Pothole!
Terminal moraines
Medial and lateral moraines
Characteristic deposits, e.g., till
Continental Glacier in Antarctica
With continued pressure, the ice moved through the hole as a long, solid rod. Ice flows in a solid state by rotation of grains, melting and refreezing, and internal slipping within the ice mass.
An empty cylinder with a capped hole near the base was filled with water and then removed and the cylinder of ice was frozen. The cap over the hole was subjected to pressure.
A Typical Glacial Advance and Retreat
Ice Ages
• Pleistocene 3 M.y.
• Permian 250-220 M.y.
• Ordovician 450 M.y.
• Precambrian
– 900-650 M.y. (Snowball Earth)– 2300 M.y.
Time (1000 Yrs) North America Alps North Europe Poland-Russia
0-18 Interglacial
18-67 Wisconsin Wurm Vistula Varsovian
67-128 Sangamon Uznach Eem Masovian
128-180 Illinoisan Riss Warthe/Saale Cracovian
180-230 Yarmouth Hoetting Holstein Sandomirian
230-300 Kansan Mindel Elster Jaroslavian
300-330 Aftonian Cromer Likhvin
330-470 "Nebraskan " Gunz Menapian
470-540 Waalian
540-550 Donau II Weybourne
550-585 Tiglian
585-600 Donau I
600-2000 About 20 Glacial Advances
2000 (2 M.Y.) Beginning of Pleistocene
4000 (4 M.Y.) Dwarf forests still in Antarctica
15 M.Y. First Glaciation in Antarctica
What Causes Ice Ages?
Within Earth• Carbonate-Silicate Cycle
• Volcanic eruptions - Sudden output of CO2
(warming) or particulates (cooling) • Mountain building - Changes in atmospheric
circulation • Continent-Ocean configuration
Outside Earth• Changes in sun (faint early sun) • Variations in Earth orbit (Milankovitch Cycles)
Is This What Pennsylvania Looked Like?
Till Shadow
Beaded valleys
Are We Headed For Another Ice Age?
• Heating & cooling in historic times
• Smoke, haze, CO2 may alter climate
• Global warming due to fossil fuels may be catastrophic in many ways, but will probably not much affect these longer-term cycles. We will have run out of fossil fuels long before the duration of a typical interglacial.
YES!!
Glacial Facts• Presently, 10% of land area is covered with glaciers.• Glaciers store about 75% of the world's freshwater.• Antarctic ice is over 4,200 meters thick in some areas.• In the US, glaciers cover > 75,000 km2, with most located in Alaska.• During the last Ice Age, glaciers covered 32% of the total land area.• If all land ice melted, sea level would rise approximately 70 meters
worldwide.• The land underneath parts of the West Antarctic Ice Sheet may be up
to 2.5 kilometers below sea level, due to the weight of the ice.• The Kutiah Glacier in Pakistan holds the record for the fastest glacial
surge. In 1953, it raced more than 12 kilometers in three months, averaging about 112 meters per day.
• The Antarctic ice sheet has been in existence for at least 40 million years.
• From the 17th to late 19th century, the world experienced a "Little Ice Age," when temperatures were consistently cool enough for significant glacier advances.
Pleistocene ice sheet at maximum extent
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