Lakes and Lakebeds

Glacial
Lake
Missoula

Glaciers

Giant Boulders

"Were there lakes on Mars? How do lakes form? How big was Glacial Lake Missoula? Were there glaciers on Mars? How do glaciers move giant boulders?"

Lakebeds on Mars

Could these be lakebeds on Mars? Scientists are still trying to determine if the layers in this image of Candor Chasma on Mars were made by water or the Martian winds. The layered sedimentary rock is now visible because of faulting and erosion. The picture shows a 1.5 km by 2.9 km (0.9 miles by 1.8 miles) area in far southwestern Candor Chasma. There are over 100 beds in this area, and each has about the same thickness (estimated to be about 10 meters (11 yards) thick). Each layer has a relatively smooth upper surface and each is hard enough to form steep cliffs at its margins. Click on the image or here for a larger image.

Layers indicate change. The uniform pattern seen here, beds of similar properties and thickness repeated over a hundred times, suggest that the deposition of materials that made the layers was interrupted at regular or episodic intervals. Patterns like this, when found on Earth, usually indicate the presence of sediment deposited in dynamic, energetic, underwater environments. On Mars, these same patterns could very well indicate that the materials were deposited in a lake or shallow sea. Malin Space Systems/NASA image and source text.

The picture at left shows sediment layers from an ancient Ice Age lake near Grand Coulee, Washington. Click on image or here for a larger view.

Click here for a detail image or close detail image of the lakebed. There is a golfball placed in the detail images to give you an idea of how thin the layers of fine sand and silt are.

Lakes and Lakebeds

Lakes are temporary geologic features Lakes are formed in depressions in the Earth's surface. Where streams or rivers flow into a lake the water tends to rise in the depression until it overflows into an outlet stream. Evaporation and seepage through the bottom help maintain the level, also. Lakes with no outlet become salty and alkaline such as Soap Lake, Washington and the Great Salt Lake, Utah. Small lakes or ponds may last only in the spring and dry up in summer when the streams that flow into it dry up. Man-made artificial lakes, called reservoirs, contain water impounded (held back) by dams. Examples are Banks Lake and Lake Roosevelt behind Grand Coulee Dam.

Lakes are one of the most temporary geologic features with few that are older than 10,000 years. Streams entering a lake carry silt and sand that is deposited in the lake which tends to fill it. Plants and animal life feed off the nutrients brought in by the streams.

A lakebed is formed as layers of silt, sand and dead organisms settle out of the lake water. As the lake becomes more shallow, plants hold the lakebed in place and soon the lake may become a marsh with a stream flowing through it. The mountain lake in the photo at right has begun this process.

Glacial lakebeds have alternating light and dark layers, varves, formed when lighter silt is deposited in summer and darker organic and clay layers are deposited in winter. This is due to very fine rock dust melting out of the glacier during the warm seasons. Each pair of layers can be counted like tree rings to estimate the age of the glacial lake.

Geology Terms

Here are some basic terms used on this page. Find more geology terms in the Glossary.

Channel: The deepest part of a river or bay.
Erosion: Lifting and removal of rock, dirt, sand and the like caused by wind, water, or glacial ice.
Geomorphology: The study of the changes in landforms due to volcanoes,
earthquakes, weather, floods, etc.
Gravel: Rounded rock fragments larger than sand.
Ice Age: A period in Earth's history when much of the continents are covered with ice sheets and glaciers.
Sediment: Collection of sand, silt, gravel and organic material that sinks to the bottom of a river, lake or ocean. Some or all of these materials may be present.
Varves: Layers of light and dark sediment on the floor of a glacial lake. Each light and dark pair indicates a year since light deposits are from rock dust from melting ice in summer and dark layers are from organic matter.

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