Thursday, 3 August 2017


9 landscape treasures left over from the Ice Age
By Sidney Stevens,
Mother Nature Network, 31 July 2017.

Glaciers reshape landscapes and transform the earth. As they advance, ice scours the ground and erodes the bedrock, picking up stones, gravel and silt, and scooping out basins and valleys in the process. As they retreat, the melting ice and streaming meltwater leave behind varied piles of acquired debris. Once a glacier is gone, things never look quite the same.

The ice sheets that descended over much of North America, northern Europe and Asia during the last glacial period, commonly called the Ice Age, were no exception. Evidence of their chilly visit, which ended about 12,000 years ago, is all around if you know what to look for. You may even have one or more of these glacial landforms in your neck of the woods or very nearby (like the glacial erratic pictured above). Read on for more about how to spot these prehistoric prizes.

1. Moraines

Photo: summonedbyfells/Flickr

As glaciers retreated after the Ice Age, their load of rocks and other debris remained behind in piles. One type, called a moraine, formed in a number of ways, including accumulating along the sides of glaciers (lateral moraines), beneath glaciers in meltwater streams (ground moraines) and where glaciers came to an end (terminal moraines). Today, these moraines typically look like hills and ridges ranging from small mounds to super-sized hills hundreds of feet high. They often exist in clusters where receding ice deposited pile after pile.

Notable moraines: Kettle Moraine (Wisconsin), Harbor Hill Moraine (Long Island, New York), Cape Ann Peninsula (Massachusetts), Dogger Bank (sand bank moraine in the North Sea that was once a landmass connecting Britain to Europe), Oak Ridges Moraine (Ontario, Canada) and Britain’s Lake District (contains several moraines).

2. Cirques

Photo: Msheppard/Wikimedia Commons

Erosion from moving Ice Age glaciers scooped out many amphitheater-shaped mountain valleys called cirques. These basins are typically encircled by high cliffs on three sides with an open section on the downhill, or lip, side where the glacier once flowed away. Imagine a tilted bowl.

Cirque stairways are a succession of cirques sitting one above the other like steps. Zastler Loch in the Black Forest of Germany is an example of a cirque stairway with three glacially carved basins.

Other notable cirques: Tuckerman Ravine (New Hampshire), Cirque of the Towers (Wyoming), Coire an t-Sneachda (Scotland) and Sniezne Kotly (Poland).

3. Tarns

Photo: Diliff/Wikimedia Commons

Fill a cirque with rain or stream water and you have a tarn. These small mountain lakes often feature a moraine at one end that acts like a dam. One of the most well-known areas for Ice Age tarns is Britain’s Lake District. This region has even spawned a new sport called tarnbagging (where lake-lovers traverse rugged countryside to visit as many tarns as possible).

Other notable tarns: Lake Ellen Wilson (Glacier National Park, Montana), Lake Tear of the Clouds (Keene, New York, on the southwest slope of Mount Marcy), Verdi Lake (Nevada) and Vel’ke Hincovo (Slovakia).

4. Eskers

Photo: James Brooks/Flickr

Cousins of moraines, eskers are deposits of sand and gravel that formed in long, winding, serpent-like ridges where debris-laden meltwater once gushed through ice-walled tunnels inside and under retreating glaciers. When the tunnels melted, sediment was deposited in snaking mounds that followed where the streams had run, often for hundreds of miles. Many highways are built on top of Ice Age eskers to cut costs, including the Denali Highway in Alaska and the “Airline Highway” segment of Route 9 in Maine.

Other notable eskers: Great Esker Park (Weymouth, Massachusetts), Mason Esker (Michigan), Kemb Hills (Aberdeenshire, Scotland), Thelon Esker (border between the Northwest Territories and Nunavat in Canada), Uppsalaasen (Sweden) and Esker Riada (system of eskers stretching across the center of Ireland).

5. Grooves and striations

Photo: Walter Siegmund/Wikimedia Commons

As glaciers plowed down mountains and across landscapes during the Ice Age, gravel and stones carried by the ice often abraded the bedrock beneath like sandpaper. What remains are scratches, grooves and gouges usually laid out in multiple long parallel lines that follow the direction the ice once flowed.

Notable examples: Glacial Grooves Geological Preserve (Kelleys Island, Ohio), Mount Rainier National Park (Washington State), Glacier National Park (Montana), Isle Royale National Park (Michigan), Lake Blanche (Utah) and Hawkes Bay (Newfoundland, Canada).

6. Kettle lakes

Photo: Amy Meredith/Flickr

Thousands of prehistoric pools, left by retreating glaciers some 12,000 years ago, dot North America, northern Europe and other formerly ice-covered landscapes around the world. These kettle lakes formed when giant ice chunks broke off as glaciers receded and were surrounded or covered by stones, soil and other debris flowing from the meltwater. When the ice chunks finally melted, what remained were bowl-shaped holes called kettles. Over the millennia many filled with water from precipitation and streams to form lakes and ponds.

Notable kettle lakes: Walden Pond (Concord, Massachusetts), Lake Ronkonkoma (Suffolk County, New York), Lake Annette (Jasper National Park, Alberta, Canada) and Seeon Lakes (Bavaria, Germany).

7. Kames

Photo: Royal Broil/Flickr

These irregularly shaped hills and mounds are similar to moraines and other elevated glacial formations, but they were created in a slightly different way. As glaciers dissolved, depressions and crevasses often formed in the ice and filled with meltwater carrying rocks and gravel. The debris in these holes finally reached the land below and was deposited in a lump. Kames tend to show up in irregular spots and may not be near other kames. However, they are often associated with kettle holes (referred to as kame and kettle topography).

Notable kames: Minnitaki Kames Provincial Park (Ontario), Mendon Ponds Park (near Rochester, New York), Sims Corner Eskers and Kames National Natural Landmark (Washington State).

8. Drumlins

Photo: Brendanconway/Wikimedia Commons

Like other glacial hills, these elongated tear-drop-shaped mounds formed from sand, gravel and rock left by melting glaciers. However, unlike moraines, kames and eskers, which are geologic junk piles left in the wake of glacial meltwater, drumlins were likely created by the ice itself in a process that scientists don’t fully understand.

They are always rounded with a higher snout side pointing up and a tail side stretching back and down. Imagine a half-buried egg. Drumlins often exist in vast fields with all of them running parallel to the direction the ice once moved. Drumlins flooded by the sea turn into islands, called drowned drumlins.

Notable drumlins: Boston Harbor Islands National Recreation Area (field of drowned drumlins), Clew Bay (Ireland), Smith-Reiner Drumlin Prairie (Wisconsin), north of the Finger Lakes (New York) and Peterborough Drumlin Field (Ontario).

9. Glacial erratics

Photo: Coaxial/Wikimedia Commons

Ever noticed a giant boulder that looks completely out of place and different from other rocks around it? It may be a glacial erratic, a large stone (some as big as a house) transported by glacial ice for hundreds of miles or carried on ice rafts that broke away during glacial flooding. Either way, these dramatic glacial gifts abound if you know where to look.

Notable erratics: Plymouth Rock (Massachusetts), Indian Rock (Montebello, New York), Norber Erratics (Yorkshire Dales National Park, U.K.), Fantastic Erratic (Cougar Mountain Regional Wildlife Park, Washington State), Clonfinlough Stone (central Ireland) and Big Rock (Foothills Erratic Train, Alberta, Canada).

Top image: Glacial erratics at Cape Purakkari, Estonia. Credit: Abrget47j/Wikimedia Commons.

[Source: Mother Nature Network. Top image added.]

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