Qualla
This photo-like image of Mount Gambier was acquired from low-earth orbit by the Landsat 7 satellite’s Enhanced Thematic Mapper Plus (ETM+) instrument. In this late spring image, vivid green fields surround the white limestone and concrete of the town. Much of the greenery is dairy pastureland, supporting one of the major local industries, cheese. Patches of deep, dark green are pine plantations, which support another mainstay of the local economy, timber. But perhaps the most striking feature is the pair of caldera lakes immediately south of the town. True to its name, Blue Lake is blue in the image, even though ETM+ acquired the image a month before the Blue Lake Days festival and the normal colour-turning of the lake. The lake turns blue at different times each year, and the satellite may have captured this image as the lake transitioned from its dark blue winter colour to the bright blue summer colour, a shift that occurs over weeks. Also, the satellite may have observed more blue light than a person standing by the lake would, since blue light tends to scatter up more than out at an angle. Thus someone immediately above the lake looking down would see a more blue-toned surface than a person standing on the rim of the caldera.
This photo-like image of Mount Gambier was acquired from low-earth orbit by the Landsat 7 satellite’s Enhanced Thematic Mapper Plus (ETM+) instrument. In this late spring image, vivid green fields surround the white limestone and concrete of the town. Much of the greenery is dairy pastureland, supporting one of the major local industries, cheese. Patches of deep, dark green are pine plantations, which support another mainstay of the local economy, timber. But perhaps the most striking feature is the pair of caldera lakes immediately south of the town. True to its name, Blue Lake is blue in the image, even though ETM+ acquired the image a month before the Blue Lake Days festival and the normal colour-turning of the lake. The lake turns blue at different times each year, and the satellite may have captured this image as the lake transitioned from its dark blue winter colour to the bright blue summer colour, a shift that occurs over weeks. Also, the satellite may have observed more blue light than a person standing by the lake would, since blue light tends to scatter up more than out at an angle. Thus someone immediately above the lake looking down would see a more blue-toned surface than a person standing on the rim of the caldera. — Photo: Jesse Allen | Public domain

Mount Gambier

Mount Gambier, South AustraliaCities in South AustraliaLimestone CoastPopulated places established in 18541854 establishments in Australia
4 min read

Each year, sometime in November, a lake in South Australia performs a trick that science still cannot fully explain. For half the year the Blue Lake of Mount Gambier sits in its crater a sullen, wintry grey. Then, as summer warms the water, it transforms - over a few weeks the whole 70-metre-deep lake floods to a vivid cobalt blue so intense it looks retouched. By autumn it fades back to grey. The Bungandidj people knew this country long before anyone gave the lake a colour for a name; to them the volcano was Berrin, and they have watched it sleep for far longer than the city built on its slopes.

The Lake That Changes Colour

The Blue Lake fills one crater of a maar volcano - a broad, shallow basin blasted out when rising magma met groundwater and exploded into steam. The water is artesian, clean enough to supply the city, and around 75 metres deep at its lowest point. The summer colour shift is thought to come from tiny calcium carbonate crystals forming in the warming water and scattering blue light, though the effect remains stubbornly hard to pin down. Stranger still, the lake hides fields of stromatolites - mounded rock structures built by microbes, among the oldest forms of life on Earth, and a genuine rarity in freshwater. A diving survey found them along the north-eastern wall, down to about 40 metres.

A City Full of Holes

Mount Gambier sits at the heart of the Limestone Coast, and limestone, given enough time and groundwater, dissolves. The result is a townscape pocked with sinkholes and water-filled caves, some of them in the middle of the city itself. The Cave Garden, known to the Bungandidj as Thugi, drops away right in the centre of town, a rose garden ringing the lip of a sinkhole that once supplied the settlement's water. A short distance away, the Umpherston Sinkhole - Balumbul - has been planted into a sunken terraced garden where ferns and hydrangeas spill down walls that were once a cave roof, floodlit at night so possums come out to feed. Engelbrecht Cave runs beneath suburban streets and draws cave divers from around the world into its flooded passages. Beyond the city, the surrounding plains are dotted with cenotes - deep, clear sinkholes whose crystalline water has made this one of the great cave-diving regions on the planet.

Berrin and the Bungandidj

The Bungandidj people are the traditional owners of this country. They called the peak Berrin and spoke of it as the home of the eagle hawk. When pastoralists arrived in the 1840s, the land was taken rapidly and violently: shepherds and settlers clashed with the original inhabitants over sheep and territory, and Bungandidj people were shot and dispossessed as the stations spread. It is a history this region no longer hides. In February 2022 the city restored Bungandidj names to its most significant places - the Blue Lake became Waawor, the Umpherston Sinkhole Balumbul - and plans are advancing to dual-name the city itself Berrin, the name it has carried in the local Aboriginal community all along.

A Sighting and a Tower

The crater was first noted by colonists in December 1800, when Lieutenant James Grant, sailing the survey brig Lady Nelson past the coast, spotted the peak and named it for Lord Gambier, an admiral of the British fleet - the first place the British named in what would become South Australia. A century later, in 1901, locals raised the Centenary Tower on the summit to mark that sighting; it still crowns the highest point and rewards the climb with a view across all the crater lakes at once. The town that grew below has since become the largest city in South Australia outside Adelaide, a service hub for timber, tourism, and a region that lives, quite literally, on hollow ground.

From the Air

Mount Gambier lies at 37.83°S, 140.78°E in south-east South Australia, about 17 km from the Victorian border. From the air the volcanic complex is unmistakable: a tight cluster of circular crater lakes - Blue, Valley, Leg of Mutton and Browne - set into the plain, with the Blue Lake's summer colour visible from a considerable distance. The cone topped by Centenary Tower marks the high point. Mount Gambier Airport (YMTG) sits a few kilometres north of the city off the Riddoch Highway and is served by regional turboprops to Adelaide and Melbourne; Naracoorte (YNRC) lies about an hour north. Expect cool, often blustery conditions exposed to the Roaring Forties, with relatively few completely clear days.

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