The Blue Lake at Mount Gambier
This image is included in a gallery "My South Australia" curated by Fairy Duff.
Mount Gambier's Blue Lake, in South Australia, is situated in a volcanic crater, exposes the crystal clear water that has filtered underground as it passes under the city through the limestone region. Each year in November the lake starts its colour change from winter steel blue to briilliant turquoise blue, before returning to its winter hue in March.
Why does Blue Lake change colour? According to the Mount Gambier visitor guide, the colour change is due to the removal of humic substances (eg tannins) from the upper part of the lake by calcite precipitation. The humic substances are yellow in colour, because they absorb blue light. The humic substances come from dead algae and land vegetation. Calcite precipitates when the lake water warms during summer. The lake water flows into the lake through limestone rocks, and the water contains lots of dissolved limestone. When the lake water warms up in summer, the limestone precipitates out of the water. As it happens, the humic substances are chemically attracted to the calcite crystals and co-precipitate with the calcite. The calcite, with humic substances attached, falls to the floor of the lake, so during summer, the surface waters have the humic substances removed and hence the natural blue colour of the water is more evident.
The Blue Lake at Mount Gambier
This image is included in a gallery "My South Australia" curated by Fairy Duff.
Mount Gambier's Blue Lake, in South Australia, is situated in a volcanic crater, exposes the crystal clear water that has filtered underground as it passes under the city through the limestone region. Each year in November the lake starts its colour change from winter steel blue to briilliant turquoise blue, before returning to its winter hue in March.
Why does Blue Lake change colour? According to the Mount Gambier visitor guide, the colour change is due to the removal of humic substances (eg tannins) from the upper part of the lake by calcite precipitation. The humic substances are yellow in colour, because they absorb blue light. The humic substances come from dead algae and land vegetation. Calcite precipitates when the lake water warms during summer. The lake water flows into the lake through limestone rocks, and the water contains lots of dissolved limestone. When the lake water warms up in summer, the limestone precipitates out of the water. As it happens, the humic substances are chemically attracted to the calcite crystals and co-precipitate with the calcite. The calcite, with humic substances attached, falls to the floor of the lake, so during summer, the surface waters have the humic substances removed and hence the natural blue colour of the water is more evident.