We are searching data for your request:
Upon completion, a link will appear to access the found materials.
Arête, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Visual Glossary of Glacial Features
This gallery primarily shows features of glaciers (glacial features) but includes features found in the land near glaciers (periglacial features). These occur widely in formerly glaciated lands, not just areas of current active glaciation.
Other picture galleries:
Fossils - - Landforms - Minerals - Rocks - -
When glaciers erode into both sides of a mountain, the cirques on either side eventually meet in a sharp, ragged ridge called an arête (ar-RET). (more below)
Arêtes are common in glaciated mountains such as the Alps. They were named from the French for "fish bone," probably because they are too jagged to be called hogbacks. This arête stands above Taku Glacier in Alaska's Juneau Icefield.
Bergschrund, SwitzerlandVisual Glossary of Glacial Features. Photo courtesy mer de glace of Flickr under Creative Commons license ( fair use policy)
A bergschrund (German, "mountain crack") is a large, deep crack in the ice or crevasse at the top of a glacier. (more below)
Where valley glaciers are born, at the head of the cirque, a bergschrund ("bearg-shroond") separates moving glacier material from the ice apron, the immobile ice and snow on the headwall of the cirque. The bergschrund may be invisible in winter if snow covers it, but summer melting usually brings it out. It marks the top of the glacier. This bergschrund is in Allalin Glacier in the Swiss Alps.
If there is no ice apron above the crack, just bare rock above, the crevasse is called a randkluft. Especially in summer, a randkluft may become wide because the dark rock next to it grows warm in the sunlight and melts the ice nearby.
Cirque, MontanaVisual Glossary of Glacial Features. Photo courtesy Greg Willis of Flickr under Creative Commons license ( fair use policy)
A cirque is a bowl-shaped rock valley carved in a mountain, often with a glacier or permanent snowfield in it. (more below)
Glaciers make cirques by grinding existing valleys into a rounded shape with steep sides. This well-formed cirque in Glacier National Park contains a meltwater lake, Iceberg Lake, and a small cirque glacier that produces the icebergs in it, both hidden behind the wooded ridge. Visible on the cirque wall is a small névé, or permanent field of icy snow. Another cirque appears in this picture of Longs Peak in the Colorado Rockies. Cirques are found wherever glaciers exist or where they existed in the past.
Cirque Glacier (Corrie Glacier), AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
A cirque may or may not have active ice in it, but when it does the ice is called a cirque glacier or corrie glacier. Fairweather Range, southeastern Alaska.05of 27
Drumlin, IrelandVisual Glossary of Glacial Features. Photo courtesy BrendanConaway via Wikimedia Commons ( fair use policy)
Drumlins are small, elongated hills of sand and gravel that form underneath large glaciers. (more below)
Drumlins are thought to form underneath the edges of large glaciers by moving ice rearranging the coarse sediment, or till, there. They tend to be steeper on the stoss side, the upstream end relative to the glacier's motion, and gently sloping on the lee side. (This is the opposite of the sculpted bedrock forms called roches moutonneés.) Drumlins have been studied using radar beneath Antarctic ice sheets and elsewhere, and the Pleistocene continental glaciers left behind thousands of drumlins in high-latitude regions in both hemispheres. This drumlin in Clew Bay, Ireland, was laid down when the global sea level was lower. The rising sea has brought wave action against its flank, exposing the layers of sand and gravel inside it and leaving behind a beach of boulders.
Erratic, New YorkVisual Glossary of Glacial Features. Photo (c) 2004 Andrew Alden, licensed to About.com. ( fair use policy)
Erratics are large boulders conspicuously left behind when the glaciers carrying them melted. (more below)
Central Park, besides being a world-class urban resource, is a showcase of New York City geology. The beautifully exposed outcrops of schist and gneiss bear traces of the ice ages, when continental glaciers scraped their way across the region leaving grooves and polish on the tough bedrock. When the glaciers melted, they dropped whatever they were carrying, including some large boulders like this. It has a different composition from the ground it sits on and clearly comes from elsewhere.
Glacial erratics are only one kind of precariously balanced rocks: those also occur under other circumstances, especially in desert settings (here's more on how those arise). In some areas they are even useful as indicators of earthquakes, or their long-term absence.
For other views of Central Park, see the walking tour of trees in Central Park North and South by Forestry Guide Steve Nix or the Central Park Movie Locations by New York City Travel Guide Heather Cross.07of 27
Eskers are long, rounded ridges of sand and gravel laid down in the beds of streams running beneath glaciers. (more below)
The low ridge winding across the landscape of the Arrow Hills, Manitoba, Canada, is a classic esker. When a great ice sheet covered central North America, more than 10,000 years ago, a stream of meltwater ran beneath it at this location. The abundant sand and gravel, fresh-made under the glacier's belly, piled up on the streambed while the stream melted its way upward. The result was an esker: a ridge of sediment in the form of a rivercourse.
Normally this kind of landform would be wiped out as the ice sheet shifts and the meltwater streams change course. This particular esker must have been laid down just before the ice sheet stopped moving and began to melt for the last time. The roadcut reveals the stream-laid bedding of the sediments composing the esker.
Eskers can be important pathways and habitats in the marshy lands of Canada, New England and the northern Midwestern states. They are also handy sources of sand and gravel, and eskers can be threatened by aggregate producers.08of 27
Fjords, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
A fjord is a glacial valley that has been invaded by the sea. "Fjord" is a Norwegian word. (more below)
The two fjords in this picture are Barry Arm on the left and College Fiord (the spelling favored by the U.S. Board on Geographic Names) on the right, in Prince William Sound, Alaska.
A fjord generally has a U-shaped profile with deep water near shore. The glacier that forms the fjord leaves the valley walls in an oversteepened condition that is prone to landslides. The mouth of a fjord may have a moraine across it that creates a barrier to ships. One notorious Alaskan fjord, Lituya Bay, is one of the most dangerous places in the world for these and other reasons. But fjords are also uncommonly beautiful, making them tourist destinations especially in Europe, Alaska and Chile.
Hanging Glaciers, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Just as hanging valleys have a disconnect with the valleys they "hang" over, hanging glaciers tumble to the valley glaciers below. (more below)
These three hanging glaciers are in the Chugach Mountains of Alaska. The glacier in the valley below is covered with rock debris. The small hanging glacier in the middle barely reaches the valley floor, and most of its ice is carried down in icefalls and avalanches rather than glacial flow.
Horn, SwitzerlandVisual Glossary of Glacial Features. Photo courtesy alex.ch of Flickr under Creative Commons license ( fair use policy)
Glaciers grind into mountains by eroding the cirques at their heads. A mountain steepened on all sides by cirques is called a horn. The Matterhorn is the type example.11of 27
Iceberg, off LabradorVisual Glossary of Glacial Features. Photo courtesy Natalie Lucier of Flickr under Creative Commons license ( fair use policy)
Not just any piece of ice in the water is called an iceberg; it must have broken off a glacier and exceed 20 meters in length. (more below)
When glaciers reach water, whether it's a lake or the ocean, they break off in pieces. The smallest pieces are called brash ice (less than 2 meters across), and larger pieces are called growlers (less than 10 m long) or bergy bits (up to 20 m across). This is definitely an iceberg. Glacial ice has a distinctive blue tinge and may contain streaks or coatings of sediment. Ordinary sea ice is white or clear, and never very thick.
Icebergs have a bit less than nine-tenths of their volume under water. Icebergs are not pure ice because they contain air bubbles, often under pressure, and also sediments. Some icebergs are so "dirty" that they carry significant amounts of sediment far out to sea. The great late-Pleistocene outpourings of icebergs known as Heinrich events were discovered because of the abundant layers of ice-rafted sediment they left across much of the North Atlantic seafloor.
Sea ice, which forms on open water, has its own set of names based on various size ranges of ice floes.
Ice Cave, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Ice caves, or glacier caves, are made by streams that run under glaciers. (more below)
This ice cave, in Alaska's Guyot Glacier, was carved or melted out by the stream that is running along the cave floor. It's about 8 meters high. Larger ice caves like this may be filled with stream sediment, and if the glacier melts without erasing it, the result is a long winding ridge of sand called an esker.13of 27
Icefall, NepalVisual Glossary of Glacial Features. Photo courtesy McKay Savage of Flickr under Creative Commons license ( fair use policy)
Glaciers have icefalls where a river would have a waterfall or a cataract. (more below)
This picture shows the Khumbu Icefall, part of the approach route to Mount Everest in the Himalayas. The glacier ice in an icefall moves down the steep gradient by flow rather than spilling in a loose avalanche, but it becomes more heavily fractured and has many more crevasses. That is why it looks more precarious for climbers than it really is, although the conditions are still hazardous.
Ice Field, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
An ice field or icefield is a thick body of ice on a mountain basin or plateau that covers all or most of the rock surface, not flowing in an organized way. (more below)
The protruding peaks within an ice field are called nunataks. This picture shows the Harding Ice Field in Kenai Fjords National Park, Alaska. A valley glacier drains its far end at the top of the photo, flowing down to the Gulf of Alaska. Ice fields of regional or continental size are called ice sheets or ice caps.
Jökulhlaup, AlaskaVisual Glossary of Glacial Features. U.S. National Park Service photo ( fair use policy)
A jökulhlaup is a glacial outburst flood, something that happens when a moving glacier forms a dam. (more below)
Because ice makes a poor dam, being lighter and softer than rock, the water behind an ice dam eventually breaks through. This example is from Yakutat Bay in southeastern Alaska. Hubbard Glacier pushed forward in the summer of 2002, blocking the mouth of Russell Fiord. The water level in the fjord began to rise, reaching 18 meters above sea level in about 10 weeks. On 14 August the water burst through the glacier and ripped out this channel, about 100 meters wide.
Jökulhlaup is a hard-to-pronounce Icelandic word meaning glacier burst; English speakers say it "yokel-lowp" and people from Iceland know what we mean. In Iceland, jökulhlaups are familiar and significant hazards. The Alaskan one just put on a good show-this time. A series of gigantic jökulhlaups transformed the Pacific Northwest, leaving behind the great Channeled Scabland, in the late Pleistocene; others occurred in central Asia and the Himalayas at that time. (Read more about jökulhlaups)
Kettles, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Kettles are hollows left behind by melting ice as the last remnants of glaciers disappear. (more below)
Kettles occur all over the places where Ice Age continental glaciers once existed. They form as the glaciers retreat, leaving large chunks of ice behind that are covered or surrounded by outwash sediment streaming from under the glacier. When the last ice melts, a hole is left behind in the outwash plain.
These kettles are freshly formed in the outwash plain of the retreating Bering Glacier in southern Alaska. In other parts of the country, kettles have turned into lovely ponds surrounded by vegetation.17of 27
Lateral Moraine, AlaskaVisual Glossary of Glacial Features. Photo (c) 2005 Andrew Alden, licensed to About.com ( fair use policy)
Lateral moraines are sediment bodies plastered along the flanks of glaciers. (more below)
This U-shaped valley in Glacier Bay, Alaska, once held a glacier, which left a thick swath of glacial sediment along its sides. That lateral moraine is still visible, supporting some green vegetation. Moraine sediment, or till, is a mix of all particle sizes, and it can be quite hard if the clay size fraction is abundant.
A fresher lateral moraine is visible in the valley glacier picture.18of 27
Medial Moraines, AlaskaVisual Glossary of Glacial Features. Photo courtesy Alan Wu of Flickr under Creative Commons license ( fair use policy)
Medial moraines are stripes of sediment running down the top of a glacier. (more below)
The lower part of Johns Hopkins Glacier, shown here entering Glacier Bay in southeastern Alaska, is stripped to blue ice in the summer. The dark stripes running down it are long piles of glacial sediment called medial moraines. Each medial moraine forms when a smaller glacier joins Johns Hopkins Glacier and their lateral moraines merge to form a single moraine separated from the side of the ice stream. The valley glacier picture shows this formation process in the foreground.19of 27
Outwash Plain, AlbertaVisual Glossary of Glacial Features. Photo courtesy Rodrigo Sala of Flickr under Creative Commons license ( fair use policy)
Outwash plains are bodies of fresh sediment strewn around the snouts of glaciers. (more below)
Glaciers release a great deal of water as they melt, usually in streams that exit from the snout carrying large quantities of fresh-ground rock. Where the ground is relatively flat, the sediment builds up in an outwash plain and the meltwater streams wander over it in a braided pattern, helpless to dig into the sedimentary abundance. This outwash plain is at the terminus of Peyto Glacier in Banff National Park, Canada.
Another name for an outwash plain is sandur, from the Icelandic. The sandurs of Iceland can be quite large.20of 27
Piedmont Glacier, AlaskaVisual Glossary of Glacial Features. Photo courtesy Steven Bunkowski of Flickr under Creative Commons license ( fair use policy)
Piedmont glaciers are wide lobes of ice that spill across flat land. (more below)
Piedmont glaciers form where valley glaciers exit from the mountains and meet flat ground. There they spread out in a fan or lobe shape, like thick batter poured from a bowl (or like an obsidian flow). This picture shows the piedmont segment of Taku Glacier near the shore of Taku Inlet in southeastern Alaska. Piedmont glaciers commonly are a merger of several valley glaciers.21of 27
Roche Moutonnée, WalesVisual Glossary of Glacial Features. Photo courtesy Reguiieee via Wikimedia Commons ( fair use policy)
A roche moutonnée ("rawsh mootenay") is an elongated knob of bedrock that has been carved and smoothed by an overriding glacier. (more below)
The typical roche moutonnée is a small rocky landform, oriented in the direction the glacier flowed. The upstream or stoss side is gently sloping and smooth, and the downstream or lee side is steep and rough. That is generally the opposite of how a drumlin (a similar but larger body of sediment) is shaped. This example is in Cadair Idris Valley, Wales.
Many glacial features were first described in the Alps by French- and German-speaking scientists. Horace Benedict de Saussure first used the word moutonnée ("fleecy") in 1776 to describe a large set of knobs of rounded bedrock. (Saussure also named seracs.) Today a roche moutonnée is widely believed to mean a rock knob that resembles a grazing sheep (mouton), but that isn't really true. "Roche moutonnée" is simply a technical name nowadays, and it's better not to make assumptions based on the etymology of the word. Also, the term is often applied to large bedrock hills that have a streamlined shape, but it should be restricted to landforms that owe their primary shape to glacial action, not preexisting hills that were merely polished by it.
Rock Glacier, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Rock glaciers are rarer than ice glaciers, but they too owe their motion to the presence of ice. (more below)
A rock glacier takes a combination of cold climate, a copious supply of rock debris, and just enough of a slope. Like ordinary glaciers, there is a large amount of ice present that allows the glacier to flow slowly downhill, but in a rock glacier the ice is hidden. Sometimes an ordinary glacier is simply covered by rockslides. But in many other rock glaciers, water enters a pile of rocks and freezes underground-that is, it forms permafrost between the rocks, and ice builds up until it mobilizes the rock mass. This rock glacier is in the valley of Metal Creek in the Chugach Mountains of Alaska.
Rock glaciers may move very slowly, only a meter or so per year. There is some disagreement over their significance: while some workers consider rock glaciers a kind of dying stage of ice glaciers, others hold that the two types are not necessarily related. Certainly there's more than one way to create them.23of 27
Seracs, New ZealandVisual Glossary of Glacial Features. Photo courtesy Nick Bramhall of Flickr under Creative Commons license ( fair use policy)
Seracs are tall peaks of ice on the surface of a glacier, commonly forming where sets of crevasses intersect. (more below)
Seracs were named by Horace Benedict de Saussure in 1787 (who also named roches moutonnées) for their resemblance to the soft sérac cheeses made in the Alps. This serac field is on Franz Josef Glacier in New Zealand. Seracs form by a combination of melting, direct evaporation or sublimation, and erosion by wind.
Striations and Glacial Polish, New YorkVisual Glossary of Glacial Features. Photo (c) 2004 Andrew Alden, licensed to About.com ( fair use policy)
Stones and grit carried by glaciers rub a fine finish as well as scratches on the rocks in their path. (more below)
The ancient gneiss and glittering schist that underlies most of Manhattan Island is folded and foliated in multiple directions, but the grooves running across this outcrop in Central Park are not part of the rock itself. They are striations, which were slowly gouged into the tough stone by the continental glacier that once covered the area.
Ice won't scratch rock, of course; the sediment picked up by the glacier does the work. Stones and boulders in the ice leave scratches while sand and grit polish things smooth. The polish makes the top of this outcrop look wet, but it's dry.
For other views of Central Park, see the walking tour of trees in Central Park North and South by Forestry Guide Steve Nix or the Central Park Movie Locations by New York City Travel Guide Heather Cross.25of 27
Terminal (End) Moraine, AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Terminal or end moraines are the main sedimentary product of glaciers, basically big dirt piles that accumulate at glacier snouts. (more below)
In its steady state, a glacier is always carrying sediment to its snout and leaving it there, where it piles up like this in a terminal moraine or end moraine. Advancing glaciers push the end moraine further, perhaps smearing it out and running it over, but retreating glaciers leave the end moraine behind. In this picture, Nellie Juan Glacier in southern Alaska has retreated during the 20th century to the position at upper left, leaving a former terminal moraine at the right. For another example see my photo of the mouth of Lituya Bay, where an end moraine serves as a barrier to the sea. The Illinois State Geological Survey has an online publication on end moraines in the continental setting.26of 27
Valley Glacier (Mountain or Alpine Glacier), AlaskaVisual Glossary of Glacial Features. U.S. Geological Survey photo by Bruce Molnia ( fair use policy)
Confusingly, glaciers in mountainous country may be called valley, mountain or alpine glaciers. (more below)
The clearest name is valley glacier, because what defines one is that it occupies a valley in the mountains. (It is the mountains that should be called alpine-that is, jagged and bare due to glaciation.) Valley glaciers are what we typically think of as glaciers: a thick body of solid ice that flows like a very slow river under its own weight. Pictured is Bucher Glacier, an outlet glacier of the Juneau Icefield in southeastern Alaska. The dark stripes on the ice are medial moraines, and the wavelike forms along the center are called ogives.27of 27
Watermelon SnowVisual Glossary of Glacial Features Watermelon snow. Photo courtesy brewbooks of Flickr via Creative Commons license ( fair use policy)
The pink color of this snowbank near Mount Rainier is due to Chlamydomonas nivalis, a type of algae adapted to the cold temperatures and low nutrient levels of this habitat. No place on Earth, except hot lava flows, is sterile.