Please note that this is a remote desert area that is prone to bushfire. Please check the weather and fire conditions before you depart, carry spare water, make sure someone knows where you are going / when to expect you back and ensure that you are equiped for the conditions. Do not attempt this cache if conditions are unfavourable.
This park is closed on days of Catastrophic Fire Danger and may be closed on days of Extreme Fire Danger.
What is the Mallee? The term Mallee refers to a multi-stemmed eucalyptus tree that grows in southern areas of Australia including south eastern South Australia, south western New South Wales and western Victoria, an area that is referred to as the Mallee Region. It is thought that the name comes from the word 'mali', which is an Aboriginal word for water, as the roots of Mallee trees contain water, stored in oversized lignotubers .
Much of this vast area was once covered by a massive lake, Lake Bungunnia, which originally formed when the Murray River became dammed by uplift of over 250 metres (820 ft) in the Grampians in Victoria during the Pleistocene about 2.5 million years ago. Lake Bungunnia, reached 40,000 square kilometres (15,000 sq mi) in area and deposited the Blanchetown Clay therein. Higher rainfall of at least 500 millimetres (20 inches) per year kept the lake filled at first, but during later times, rainfall was insufficient, and saline lakes formed, depositing dolomite. Even today, some saline lakes remain as a remnant of the vast lake.
The Mallee Region is predominantly covered in dunes that are derived from the Parilla Sands, as well as other marine and freshwater sediments, after Lake Bungunnia dried up in the Middle Pleistocene. About 500,000 years before present, linear dunes first formed in the region and were stabilised by vegetation. These were then covered by newer dunes formed by wind-blown sand during the last glacial stage, and parna (dust blown from dry salt lakes and saltpans), that were spread across the area.
Mallee trees are mainly restricted to the dunes, the swales (the space between dunes) are covered by grasses and forbs that grow on the clay-rich soil.
The Mallee Region has a low rainfall (325 +/- 50mm per year) and has sandy soils that are low in nutrients. Rainfall in this area predominantly occurs in winter and the environment is hot and dry in the summer.
Aboriginal people are known to have visited the Ngarkat area, however it is unclear whether the area was permanently occupied by Aboriginal people.
The Fish Ponds at this location are a series of interconnecting clay pans that collect and channel water that is trapped between the surrounding sand dunes.
They fill with water in the winter months, providing access to surface water that is rare in the desert, supporting a wide variety of wildlife including kangaroos, emus, insects, a diverse bird life and frogs.
To complete this earthcache, you will need to visit the Fish Ponds and answer questions designed to enhance your observation of and learning from the unique geology and hydrology of this area. Please email the answers to the questions to the cache owner in order to gain permission to log this earthcache.
Please post your answers to question 1 in your cache log so that the cache page becomes a record of the water levels in the ponds, but do not post your answers to questions 2 or 3 with your cache log. Photos showing the water level are encouraged but not required in order to log this earthcache.
1. Is there water in the Fish Ponds? If so, how deep is it? and is salty or fresh?
You can test this by dipping a finger in the water and then tasting it if you want, or alternatively by looking to see if there is a build up of crystalised salt at the waters edge, algae growing in the water, etc. Please describe the process that you used when answering the question.
2. If the water is salty or there is evidence of salt in the clay plan, then where do you think that the salt has come from? - do not post your answer to this part of the question online
3. As explained on this cache page and on the walking track signs, the Fish Ponds are a series of interconnecting clay pans that collect water from the surrounding sand hills. Please describe the colour and consistency of the clay. How does it vary from the surrounding sand? And how does it assist with the retention of water?
You may log the cache as soon as you submit your answers. The cache owner will review your answers and respond to if there are any issues or concerns. Cache finders will be contacted and their cache logs will be discretely deleted if answers are not sent to the cache owner within a reasonable time frame of the cache being logged online.
References
http://www.southernmallee.sa.gov.au/webdata/resources/files/TRACKS_MALLEE.pdf
http://austhrutime.com/mallee.htm
https://en.wikipedia.org/wiki/Murray_Basin