Gilgai facts for kids

A gilgai is a special kind of small, temporary lake or pond. It forms in places where the soil is made of a type of clay that expands when wet and shrinks when dry. The word "gilgai" also describes the whole bumpy landscape in these areas, which has both small hills (mounds) and dips (depressions).

The name "gilgai" comes from an Australian Aboriginal word that means "small water hole." These pools are usually only a few metres wide and less than 30 centimetres deep. But sometimes, they can be several metres deep and up to 100 metres across! You can find gilgais all over the world, especially where there are cracking clay soils and clear wet and dry seasons. People sometimes call gilgais by other names like "melonholes," "crabholes," or "hogwallows."

A gilgai landscape in Queensland, Australia

How Do Gilgais Form?

Gilgais form in a type of soil called vertisols. This happens because of repeated cycles of the clay soil getting wet and swelling, then drying out and shrinking. This process is called argillipedoturbation.

Here's how it works:

• When the soil dries, it cracks.
• Loose soil material then falls into these cracks.
• When the soil gets wet again, it swells. But now, the cracks are full of loose soil, so the pressure from the swelling soil pushes it sideways.
• This sideways push creates a mound (a small hill) between the cracks and a depression (a dip) where the crack was.
• The depressions then collect water, making them even wetter. This causes them to swell more and crack even deeper when they dry out.
• Each time the soil swells, shrinks, and cracks, the pattern becomes more noticeable. Eventually, the land is covered in a repeating pattern of mounds and depressions. The depressions hold surface water during the wet seasons.

Where Can You Find Gilgais?

Australia has a lot of cracking clay soils and very clear wet and dry seasons. These conditions are perfect for gilgais to form.

Other places around the world where you can find gilgais include:

• Central Russia
• Parts of the United States, like South Dakota and Texas

Gilgais look a bit like the patterned ground found in very cold places. However, those patterns are formed by repeated freezing and thawing of the soil, not by the soil getting wet and dry like gilgais.

Why Are Gilgais Important?

Gilgais have been very important throughout history, especially for people and animals.

Water for People and Animals

• For Indigenous Australians, gilgais were a vital source of water. They allowed people to travel and find food in areas that didn't have permanent water sources.
• Early Australian farmers, called pastoralists, also used gilgais to water their livestock. This meant their animals could graze in these areas during certain seasons.
• Today, with modern water wells and pumps, gilgais are less crucial for human water supply.

Challenges for Farmers

• Farmers often see gilgais as a problem. The constant movement of the soil can damage buildings, roads, and railway lines.
• The bumpy ground also makes it hard to harvest crops.
• Seasonal water in grazing lands can make it difficult to control farm animals. It also provides water for vermin like feral pigs and kangaroos.

Ecological Importance

Even though they can be a nuisance for farmers, gilgais are still very important for nature. They provide water for many different animals and plants. For example:

• Crayfish dig burrows in the wet basins.
• Ants build up the mounds, which helps make the formations even bigger through a process called bioturbation (when living things move soil).

Images for kids

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  A gilgai landscape in Queensland, Australia

See also

In Spanish: Gilgai para niños