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