Australian
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Teacher’s notes

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This clip begins with a hovercraft being driven across Lake Eyre by John and Roma Dulhunty. It shows shots of Lake Eyre with water in it as the narrator tells us that the salt crust forming around the edge of the lake is wafer-thin now, but will be 18 inches (15 cm) thick in the middle of the lake as it returns to its normal dry state. Background music underscores his comments. John Dulhunty is then shown talking passionately about how lucky he and Roma have been to see, over the previous few years, the greatest flooding of the lake in 500 years, after seeing it as a dry lake, its normal condition. He says they are witnessing a demonstration of how the lake was formed 3,000 years ago.

Educational value points

• Lake Eyre is the largest dry salt lake in Australia. Situated in South Australia on the south-western end of the Simpson Desert, it covers 9,323 sq km. Its lowest point is about 15 m below sea level, which makes it the lowest point on the continent. Lake Eyre is actually two lakes, Lake Eyre North, which is 144 km long and 77 km wide, and Lake Eyre South, which is 64 km long and 24 km wide. They are connected by the 13-km-long Goyder Channel.

• The Eyre Basin is the huge endoreic system that surrounds the lake and covers one-sixth of the continent. 'Endoreic’ describes a terminal, or closed, basin with internal drainage and no outlet to the sea. ('Endoreic’ is from the Greek endo, meaning inside, and rhein, meaning to flow.) Water does not flow out of the lake via rivers, underground flow or diffusion through rock or permeable material. Any rain that falls or water that flows from a river into the lake remains, only leaving the system by evaporation.

• Lake Eyre is both a dry salt lake and a 'playa’ lake, which is a shallow lake with a wet–dry cycle. When there is heavy flooding Lake Eyre becomes an inland sea. The lake is filled in three ways: from Cooper Creek, from the Diamantina River or from the lake’s western desert tributaries. A major filling of the lake occurs when a combination of two or three of these watercourses carries floodwaters into the lake.

• In the clip John Dulhunty (1911–94) says that the current (1970s) level of flooding has not occurred on the lake for 500 years. There have been many minor floodings of Lake Eyre but the flood Dulhunty is referring to is the major flood of 1973, which peaked in 1974 and lasted until 1977. In 1984 Lake Eyre South filled, an event not previously recorded, and overflowed into Lake Eyre North. This happened again in 1989 and in 1990, when water from Cooper Creek reached Lake Eyre for the first time since 1974.

• After retirement, geologist John Dulhunty undertook a number of expeditions to Lake Eyre with his wife, Roma. They made these expeditions to document the major sequence of wet–dry cycles at the lake and the sedimentation and geomorphic (physical features of the Earth’s surface) changes the lake was subject to. Roma also wrote three books about their expeditions to Lake Eyre and these books are in the Rare Books and Special Collections Library of the University of Sydney.

• A hovercraft, such as the one shown in the clip, is a vehicle that is supported by a cushion of air blown out under pressure. The first recorded design for such a vehicle appeared in 1716 and was produced by Emanuel Swedenborg, a Swedish designer, philosopher and theologian. In the mid-1870s a British engineer, Sir John Isaac Thornycroft, built a number of hovercraft models. Finnish engineer Toivo J Kaario began designing an air-cushion craft in 1931 but did not proceed with it. Christopher Cockerel of Britain, who coined the term 'hovercraft’, produced a successful model that was launched in 1959.

• Due to the flat, hard nature of the lake when dry, Donald Campbell (1921–67) chose it as the venue for an attempt to break the then world land speed record. The lake was chosen because it had not rained there for 20 years and the surface was as hard as concrete. When Campbell arrived in March 1963 light rain began to fall and in late May the rain became heavier and the lake flooded. The attempt was abandoned but Campbell returned in 1964 and in July of that year he set a record of 403.1 miles per hour (648.9 km per hour) in his jet-propelled car Bluebird CN7.

• Lake Eyre is named after Edward John Eyre (1815–1901), an English explorer who also gave his name to Eyre Peninsula in SA. John Eyre arrived in Sydney, New South Wales, in 1833 and became a pioneer overlander, driving sheep from Sydney to Adelaide. He explored the desert north-west of Adelaide, searching for a route to inland Australia, and in 1840 first sighted the lake that now bears his name.

John and Roma Dulhunty drive a hovercraft across Lake Eyre, followed by shots of Lake Eyre with water in it and close-ups of the salty surface.
Narrator The pilgrimage is nearly over for another year. It will probably be the last occasion they’ll see water in the lake. If it doesn’t rain by the time they return next year, the salt crust that’s already starting to form around the edges will have taken over the lake. It’s only wafer-thin now but later, in the middle, it’ll grow to a depth of 18 inches. The lake is slowly returning to normal, becoming, once again, a dry salt lake.

John Dulhunty is interviewed.
John Dulhunty, geologist Well, we were tremendously impressed with it as a dry lake but, of course, when it filled with water – with the greatest flooding for 500 years – to the geologist, that was something quite out of this world. The thing is that the processes which had moulded Lake Eyre, back to 3,000 years ago, were turned on for us to actually see them as a demonstration. Well, this is something beyond anything we could possibly have hoped for. It’s just as though you had been reading about Moses crossing the Red Sea when the waters parted and you suddenly looked out and there was the Red Sea opening up, as though you were seeing it happening. We saw, over the last few years, reproduced for us, the process that had been going on for 3,000 years and it was the first time for 500 years that it had happened so we’re a bit lucky to be here when that happened, weren’t we?