Glaciers and Ice Ages in Virginia

the ice sheet stopped in Pennsylvania 18,000 years ago at the peak of the Wisconsin glaciation
the ice sheet stopped in Pennsylvania 18,000 years ago at the peak of the Wisconsin glaciation
Source: ESRI, ArcGIS Online glacial advance

A series of "ice ages" started 2.6 million years ago, perhaps triggered by the closing of the Panama Seaway and alterations in the salinity in different parts of the oceans, changes in the earth's orbit, large-scale changes in ocean currents and the East Asian Monsoon, and/or lower carbon dioxide levels in the atmosphere caused by the weathering of the Himalayas. Four major continental ice sheets grew southward, then retreated. The last, the Wisconsin stage, started about 75,000 years ago.1

The Laurentide Ice Sheet grew during the Wisconsin stage. It stopped north of the Ohio River and the Pennsylvania Turnpike, and at modern New York City. During the furthest extent of the ice that ended 18,000 years ago, Virginia was never buried underneath a thick layer of ice.

There may have been a small mountaintop glacier on Mount Rodgers, the highest peak in Virginia at 5,729 feet, but no evidence of glaciation remains. Peaks in Virginia may have been covered with snow during the winter, but wind and sun removed the snow before it was compressed to form glaciers. Mount Mitchell in North Carolina is 6,684 feet high, and in the 1970's there was a claim of glacial scratches on the bedrock of that peak. However, later investigation revealed that cables used in logging operations had carved the grooves.2

Virginia still experienced significant impacts from the cold climate in the last Ice Age. The Laurentide Ice Sheet altered the location of the Atlantic Ocean shoreline. At the start of the last glacial period 125,000 years ago, sea level was about 15' higher than today. Sea level dropped 400' as water was trapped in the ice sheet. The Continental Shelf was exposed, and the shoreline was as much as 75 miles east of modern Virginia Beach.

The winds, rains, and temperature of Virginia's paleoclimate were affected significantly by the presence of the Laurentide Ice Sheet. Cold dry winds blasted south, bring only 25" of moisture annually compared to over 40" today. Paleo-Indians, the earliest humans in Virginia, sheltered on the sandy hills along the Nottoway River at Cactus Hill and Blueberry Hill. They preferred north-facing slopes even though the sun was warmer on south-facing slopes, because the winds swept away the biting insects in the river valley.3

The ice was 2000' thick on top of modern Manhattan Island, taller than the Freedom Tower. The edge of the ice sheet stayed at the same location long enough for meltwater to deposit a massive amount of debris scraped up by the glacier, forming Long Island.4

The weight on the ice sheet pressed down on the bedrock, depressing the land into southern Pennsylvania. The land further south flexed in response to the pressure and bent upwards.

As a result, at the peak of the Ice Age the land along Virginia's coastline was raised up. Sea level was already as much as 400 meters lower because so much water was trapped in the glaciers, and the eastern coastline of Virginia was as much as 40 miles east of the current location. The flexing earth raised the Virginia coastline even higher and extended the Coastal Plain even further to the east.

sea level rise Today, the ice sheet has retreated far north and the depressed bedrock in Pennsylvania is rebounding upwards. The area along the current Atlantic Ocean shoreline, the crust that was uplifted in response to the nearby ice, now is sinking back down. That adjustment, combined with global warming, is causing faster-than-average sea level rise along Virginia's Atlantic Ocean shoreline and in the Chesapeake Bay.5

In the Valley and Ridge province, blocks of stone cracked loose from the bedrock on the sandstone ridges, slid downhill, and created piles of boulders in a talus slope below the quartzite bedrock. When the climate warmed, the hillsides stabilized and the forests returned. Trees grew below the talus pile and above their eroding bedrock source, but not on the barren boulders themselves.

The freezing and thawing cycle was less intense, however, and few new rocks were added to the talus in the last 10,000 or so years. The pile of talus rock slid downhill under the force of gravity, but new talus was no longer added regularly on the uphill edge of the talus pile. Over centuries, a gap developed between the source bedrock and the talus pile, and trees grew in that gap. The isolated block fields - below the trees and now separated from the layer of sandstone that eroded to form the original talus pile - stand out against the forested mountainsides today, remnants of an ancient climate.6

"Block fields" are still visible on the western slope of Massanutten Mountain. During the last glacial period, cold winds blew across the mountains and little vegetation could grow there. Cracks in the sandstone bedrock widened as the moisture in them froze. The ice froze and melted repeatedly, creating The Channels on Clinch Mountain at the border of Russell and Washington counties.7

the ice sheet that stopped in Pennsylvania affected the creation of The Channels over 200 miles away
the ice sheet that stopped in Pennsylvania affected the creation of The Channels over 200 miles away
Source: ESRI, ArcGIS Online

Glaciers did not carve the landscape in southwestern Virginia, but the Ice Age climate (as well as earthquakes) may have been a factor in creating the largest known landslides in eastern North America. For 20 miles, land has slumped along the eastern slope of Sinking Creek Mountain west of modern-day Blacksburg.

When the climate was colder, vegetation was less and erosion was evidently higher. Soil washed away at the base of rock layers on the mountain, and earthquakes may have triggered a series of massive landslides until 10,000 year ago.8

Virginia and the "Snowball Earth/Popsicle Planet" Theory

Climate of Virginia

How Will the Environment of Virginia Change?

Virginia Ecosystems

The Channels was created when joints and fractures in the sandstone at the top of Clinch Mountain were widened by the freezing and thawing of ice during the Pleistocene The Channels was created when joints and fractures in the sandstone at the top of Clinch Mountain were widened by the freezing and thawing of ice during the Pleistocene
"The Channels" was created when joints and fractures in the sandstone at the top of Clinch Mountain were widened by the freezing and thawing of ice during the Pleistocene

Links

References

1. "Glacial Geology Ice Ages in the Geological Record," Indiana Geological and Water Survey, https://igws.indiana.edu/MarionCounty/IceAgeGeoRecord.cfm; "New theory on cause of ice age 2.6 million years ago," Science Daily, June 27, 2014, https://www.sciencedaily.com/releases/2014/06/140627094404.htm; "The history of ice on Earth," New Scientist, May 24, 2010, https://www.newscientist.com/article/dn18949-the-history-of-ice-on-earth/; Y. J. Wang,, H. Cheng, R. L. Edwards, Z. S. An, J. Y. Wu, C.-C. Shen, J. A. Dorale, "A High-Resolution Absolute-Dated Late Pleistocene Monsoon Record from Hulu Cave, China," Science, Volume 294, Issue 5550 (December 14, 2001), http://doi.org/10.1126/science.1064618 (last checked June 8, 2018)
2. John B. McKeon, John T. Hack, Wayne L. Newell, James O. Berkland and Loren A. Raymond, "North Carolina Glacier: Evidence Disputed," Science, New Series, Volume 184, Number 4132 (April 5, 1974), p.89, http://www.jstor.org/stable/1737466 (last checked April 19, 2017)
3. "Virginia Wasn't Recognizable During Ice Age," Daily Press, December 31, 2000, http://articles.dailypress.com/2000-12-31/features/0012280150_1_ice-sheets-ice-age-massive-ice; Michael F. Johnson, "Cactus Hill, Rubis-Pearsall and Blueberry Hill: one is an accident; two is a coincidence; three is a pattern predicting "old dirt" in the Nottoway river valley of Southeastern Virginia, U.S.A.," PhD thesis, University of Exeter, 2012, p.60, https://ore.exeter.ac.uk/repository/handle/10871/9541; "Sea Level Rise, After the Ice Melted and Today," National Aeronautics and Space Administration, January 2007, https://www.giss.nasa.gov/research/briefs/gornitz_09/; Kurt M. Cuffey, Shawn J. Marshall, "Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet," Nature, Volume 404 (April 6, 2000), http://doi.org/10.1038/35007053 (last checked June 8, 2018)
4. "How the Ice Age Shaped New York," New York Times, June 5, 2018, https://www.nytimes.com/2018/06/05/science/how-the-ice-age-shaped-new-york.html (last checked June 8, 2018)
5. "Glacial Rebound: The Not So Solid Earth," National Aeronautics and Space Administration, August. 26, 2015, https://www.nasa.gov/feature/goddard/glacial-rebound-the-not-so-solid-earth; "Sinking Atlantic Coastline Meets Rapidly Rising Seas," Scientific American, April 14, 2016, https://www.scientificamerican.com/article/sinking-atlantic-coastline-meets-rapidly-rising-seas/ (last checked June 8, 2018)
6. "Glimpses of the Ice Age from I-81," US Geological Survey, 1998, http://pubs.usgs.gov/gip/i81/i81.pdf (last checked February 19, 2015)
7. "Channels State Forest," Virginia Department of Forestry, http://www.dof.virginia.gov/infopubs/_state-forests/CHSF-2013-05_pub.pdf (last checked June 8, 2018)
8. "The Mountain that Moved - Ancient Giant Landslides," US Geological Survey, 2000, http://pubs.usgs.gov/gip/mountain/mountain.pdf (last checked June 8, 2018)

glacial advance
glacial advance... to Pittsburgh, but not into modern-day Virginia
Source: US Geological Survey, National Atlas


Rocks and Ridges - The Geology of Virginia
Virginia Places