Sunday, September 27, 2015

Why did the sink hole happen at Rainbow Beach?

Sink hole north of Rainbow Beach.  Image source: Facebook: Kieren Hudson
It might be time to experience camping at Inskip Point before it disappears.   Inskip Peninsula is an isthmus of sand that once connected Fraser Island with the mainland, but is now separated and is just a thin strip of sand sandwiched between the Pacific Ocean and Tin Can Bay.

Inskip is one of the most popular camping spots in South East Queensland hosting thousands of campers during school holidays.  It lies across a small channel of water from the southern tip of Fraser Island at the entrance to Tin Can Bay, 10 minutes drive north of Queensland's Rainbow Beach.  Most people travelling to Fraser Island drive from Rainbow Beach north along the peninsula to Inskip point, from where they catch a barge across to the southern tip of Fraser Island.

Around 11pm on Saturday, 26 September, a car, a caravan and a camping trailer were swallowed by a giant sinkhole that opened up at the Inskip Point camping ground.  Thankfully no people were injured.  Police estimated the hole to be about 100 metres by 100 metres and around three metres deep.

The last sink hole occurred in 2011 a little further north of this one at the MV Beagle campsite, which is about half way up the peninsula.  There are plenty of opinions about why the sink hole happened at Rainbow Beach.  However, it is actually one of many that have occurred over the years and which will continue to happen.

On the Clayton's Towing Facebook page, Debbie Campbell Myers posted this excerpt from The Brisbane Courier of 3 July 1901
LANDSLIP AT INSKIP The harbour-master at Maryborough (Captain Boult) has Informed the Port master that the coxswain at Inskip had advised him that a land-slip has occurred there, by which a truck and part of the boat tram gear was lost, but the boats and a spare bar buoy were saved with difficulty. The beacon and light-stand near the boatshed are liable to go at any time. There is now 14ft. of water near the beacon, and the next spring tides will show whether any more trouble may be expected.
Back in 2011, the Brisbane Times reported this opinion as to why the sink hole happened at Rainbow Beach:
Canberra-based landslide and disaster risk management scientist Dr Marion Leiba said the dramatic sinkhole-like conditions were likely caused by an “eddy” or “loop” current creating turbulence in the water and destabilising sand.

``Sand is permeable which means the water gets in to it and when you get enough water pressure, it holds the grains apart and it turns in to quicksand,'' she said.

``It loses cohesion and it just sort of collapses down.  It's just sort of s
ucked down in to the bottom of the water."
 View of Inskip looking south to Rainbow Beach - showing point where barges depart to Fraser Island (Double Island Point in the very far distance).  Given the Pacific Ocean is crashing into one side, there is no surprise that the peninsula is slowly subsiding into the ocean.  Image source:
Image source:
The Wide Bay Bar at the entrance to the channel between Fraser and Inskip is notoriously treacherous.   If you love history, check out this fabulous recounting of the history of the Inskip Point Light and Signal Station.  

This film was recorded in 2005, moments earlier they were a number of 4X4 parked in this section of beach with guys fishing near by.   These sink holes appear every now and again along Inskip Beach near where the ferrys cross between Inskip Point and Fraser Island.


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