Glaciers and Ice Ages in Virginia

Virginia was not covered by glaciers in the latest Ice Age. The continental ice sheets stopped at roughly the location of the Ohio River and the Pennsylvania Turnpike.

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

Virginia was still affected by the last ice sheet. At one time, when sea level was as much as 400 meters lower because so-o-o-o much water was trapped in the glaciers, the eastern coastline of Virginia was far to the east. When the glaciers melted during periods warmer than today, sea level was as much as 100 feet higher and the Virginia coastline was close to the current route of Interstate 95.1

The weight on the ice sheet in Pennsylvania pressed down on the bedrock, depressing the land underneath. In response, the land apparently bent upwards further south and east. 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, crust that was uplifted in response to the nearby ice, 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.

Scratches on the bedrock of Mount Mitchell in North Carolina may be glacial striations, etched when a small mountaintop glacier flowed (albeit slowly) across the bedrock. Rocks trapped in the ice at the bottom of the glacier left a trail, just like a cat claws scraping across fine furniture can leave marks. Virginia is further north than Mount Mitchell, but apparently the mountains in Virginia were too low to be glaciated. However, we can still see the effects of the last Ice Age on the Blue Ridge.

"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 and and then the ice melted repeatedly. Blocks of stone cracked loose from the bedrock, slid downhill, and created piles of boulders in a talus slope below the quartzite bedrock.

sea level rise

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.2

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.3

Virginia and the "Snowball Earth/Popsicle Planet" Theory

References

1. Schweitzer, Peter N. and Thompson, Robert S., Global Gridded Pliocene and Late Quaternary Sea Level, U.S. Geological Survey Open-File Report 96-000, URL:http://geochange.er.usgs.gov/pub/sea_level/, April 15, 2000
2. "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)
3. "The Mountain that Moved - Ancient Giant Landslides," US Geological Survey, 2000, http://pubs.usgs.gov/gip/mountain/mountain.pdf (last checked February 19, 2015)


Rocks and Ridges - The Geology of Virginia
Virginia Places