Earth Science Logging Questions
Please send answers via the geocaching message system. Do not post them in your log.
1. Colour Observation
Describe the colour of the lake at the time of your visit. What shade do you see?
Based on the description below, explain what geological or biological factors might be influencing the colour today.
2. Salinity Evidence
Wander down to the edge of the lake or shoreline.
What visible evidence of salinity do you see? Examples: salt crusts, white powdery residue, floating salt, none visible.
Explain briefly what this tells you about the current evaporation conditions.
3. Photo Requirement
Take a photo with you or a personal item with the lake in the background.
Reminder - this is an earthcache - there is no physical container.
Please stay on designated paths and avoid damaging the fragile salt crusts. Wildlife and microorganisms depend on the lake's natural cycles.
The rest area here has toilets, picnic tables and shade where drivers can stop to take in the lake's stunning scenery.
If you want to increase your chances of seeing the lake at the rosiest of pinks, the best time to visit is in late summer and autumn when it is more likely that the pink-loving microrgnaisms will grow in the warmer conditions. There are walking tracks around the lake where you can enjoy the views of the pink waters.
PINK LAKE GEOLOGY
Pink Lake is one of the distinctive seasonal salt lakes of the Wimmera region, located a short distance from Dimboola. The lake’s striking pink colour varies throughout the year depending on weather, water levels, salinity, and the presence of specialised microorganisms.
What you can observe at GZ ?
Depending on the season, you might see:
- A bright or pale pink lake surface
- Crystalline salt crusts along the edges
- A shallow, muddy or clayey lake bed
- Layers of evaporite minerals forming patterns
- Salt “rafts” or floating crusts in warmer months
Why is the lake pink?
The colour primarily comes from
- Halophilic (salt-loving) algae, especially Dunaliella salina, which produces beta-carotene, a reddish pigment.
- the colour of the lake is a result of the reddish pigments called bacteriorhodopsin that are produced by the algae
- high salinity, which stresses these organisms and enhances pigment productioon.
The pink colour intensity changes according to the time of year, temperature, amount of cloud cover, and water level. Fresh nutrients that wash into the lake after heavy rain cause the growth of algae. The colour fluctuates between being a mild salmon and a vivid bubblegum pink. Although the pink tint cannot be assured, the stunning shifting tones of this lake will not disappoint visitors.
The exact hue at any time depends on:
- salt concentration in the remaining water
- evaporation rate
- sunlight intensity
- water depth
- temperature
- seasonal rainfall
How do salt lakes form here?
Pink Lake is part of the Wimmera River terminal drainage system, where low-lying depressions collect water during wetter periods. Because the region has high evaporation and low overall rainfall, water often evaporates faster than it arrives. Over time dissolved salts accumulate, creating shallow playa lakes with hypersaline brines.
Causes of Salinity
- Climate: High evaporation rates, especially in summer, mean rainfall often doesn't exceed evaporation, preventing flushing of salt from the landscape, pushing it into low-lying areas.
- Land Clearing: Removing native vegetation for agriculture has raised groundwater levels, bringing dormant, deep-seated salt to the surface and into waterways.
- Natural Salt: Salt is naturally present in the region's soils and groundwater, but land use changes intensify its concentration.
Salt originates from:
- Weathering of local rocks
- Groundwater movement
- Ancient marine sediments in the region
- Concentration through repeated evaporation cycles
Evidence of high salinity include
As water evaporates, salt crystallizes and forms white crusts on the lakebed and edges, contrasting with the pink water.
- visible salt crusts on soil with bare, salty patches
- salt-tolerant plants or plant dieback
- corosion of infrastructure like roads and pipes
Salt lakes typicaly don't go pink until the salt concentration is over 20%. That's over five times that of sea water !
Salt has been harvested from the lake since the 1860s and on average, 20 tonnes a year are harvested by the Mount Zero Olive company working in conjunction with the Barengi Gadjin Land Council.