A moraine is material left behind by a moving glacier. This material is usually soil and rock. Just as rivers carry along all sorts of debris and silt that eventually builds up to form deltas, glaciers transport all sorts of dirt and boulders that build up to form moraines.
To get a better idea of what moraines are, picture yourself with a toy bulldozer on a lawn that has a bunch of dry leaves all over it. When you run the bulldozer through the leaves, some of them get pushed aside, some of them get pushed forward, and some of them leave interesting patterns on the grass. Now think of these patterns and piles of pushed-away leaves—moraines—stretching for kilometers on the Earth.
Moraines only show up in places that have, or used to have, glaciers. Glaciers are extremely large, moving rivers of ice. Glaciers shape the landscape in a process called glaciation. Glaciation can affect the land, rocks, and water in an area for thousands of years. That is why moraines are often very old.
Moraines are divided into four main categories: lateral moraines, medial moraines, supraglacial moraines, and terminal moraines.
A lateral moraine forms along the sides of a glacier. As the glacier scrapes along, it tears off rock and soil from both sides of its path. This material is deposited as lateral moraine at the top of the glacier’s edges. Lateral moraines are usually found in matching ridges on either side of the glacier. The glacier pushes material up the sides of the valley at about the same time, so lateral moraines usually have similar heights.
If a glacier melts, the lateral moraine will often remain as the high rims of a valley.
A medial moraine is found on top of and inside an existing glacier. Medial moraines are formed when two glaciers meet. Two lateral moraines from the different glaciers are pushed together. This material forms one line of rocks and dirt in the middle of the new, bigger glacier.
If a glacier melts, the medial moraine it leaves behind will be a long ridge of earth in the middle of a valley.
A supraglacial moraine is material on the surface of a glacier. Lateral and medial moraines can be supraglacial moraines. Supraglacial moraines are made up of rocks and earth that have fallen on the glacier from the surrounding landscape. Dust and dirt left by wind and rain become part of supraglacial moraines. Sometimes the supraglacial moraine is so heavy, it blocks the view of the ice river underneath.
If a glacier melts, supraglacial moraine is evenly distributed across a valley.
Ground moraines often show up as rolling, strangely shaped land covered in grass or other vegetation. They don’t have the sharp ridges of other moraines. A ground moraine is made of sediment that slowly builds up directly underneath a glacier by tiny streams, or as the result of a glacier meeting hills and valleys in the natural landscape. When a glacier melts, the ground moraine underneath is exposed.
Ground moraines are the most common type of moraine and can be found on every continent.
A terminal moraine is also sometimes called an end moraine. It forms at the very end of a glacier, telling scientists today important information about the glacier and how it moved. At a terminal moraine, all the debris that was scooped up and pushed to the front of the glacier is deposited as a large clump of rocks, soil, and sediment.
Scientists study terminal moraines to see where the glacier flowed and how quickly it moved. Different rocks and minerals are located in specific places in the glacier’s path. If a mineral that is unique to one part of a landscape is present in a terminal moraine, geologists know the glacier must have flowed through that area.
Moraines of Kilimanjaro
Moraine landscapes are found all over the world and are still being formed. Glaciers in the Chugach Mountains, near the Arctic Circle in the U.S. state of Alaska, make fresh moraine deposits every day. Meanwhile, the melting snows on Tanzania's Mount Kilimanjaro are leaving fresh moraine in equatorial Africa.
That's No Speed Bump
Kaskawulsh Glacier in Canada has a ridge of medial moraine that stretches one whole kilometer (0.6 miles) wide.
Term Part of Speech Definition Encyclopedic Entry bulldozer Noun
vehicle used for moving large obstacles, such as boulders or trees.
remains of something broken or destroyed; waste, or garbage.
the flat, low-lying plain that sometimes forms at the mouth of a river from deposits of sediments.
Encyclopedic Entry: delta deposit Verb
to place or deliver an item in a different area than it originated.
end moraine Noun
material deposited at the end of a glacier. Also called a terminal moraine.
person who studies the physical formations of the Earth.
process of a glacier carving out a landscape.
mass of ice that moves slowly over land.
Encyclopedic Entry: glacier ground moraine Noun
materials such as earth and gravel deposited by a glacier as it retreats.
land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet).
Encyclopedic Entry: hill lateral moraine Noun
material deposited at the edges of a glacier.
area of grass mowed, watered, and maintained by people.
medial moraine Noun
material that is built up where two glaciers meet to form a new glacier.
inorganic material that has a characteristic chemical composition and specific crystal structure.
material, such as earth, sand, and gravel, transported by a glacier.
Encyclopedic Entry: moraine rain Noun
Encyclopedic Entry: rain ridge Noun
long, narrow elevation of earth.
river bed Noun
material at the bottom of a river.
natural substance composed of solid mineral matter.
solid material transported and deposited by water, ice, and wind.
Encyclopedic Entry: sediment silt Noun
small sediment particles.
Encyclopedic Entry: silt soil Noun
top layer of the Earth's surface where plants can grow.
supraglacial moraine Noun
material that builds up on the surface of a glacier.
terminal moraine Noun
material deposited at the end of a glacier. Also called an end moraine.
one of a kind.
depression in the Earth between hills.
all the plant life of a specific place.
movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.