Ok so here’s a quickie, literally, it will be fast and there is an element of madness to it!
There are literally hundreds of outstanding locations in the Kimberly’s but I think you will have to agree that The Horizontal Falls are one of the most amazing natural features. In 2013 Sir. David Attenborough Described this area as "One of the greatest wonders of the natural world".
The tidal waterfalls effecionatly known as “The Horries” are located in Talbot Bay within the Buccaneer Archipelago, they are unlike any other waterfall, the water passes horizontally!
You will hear everyone refer to them as ‘waterfalls’, but in actual fact this natural phenomenon actually consists of intense tidal currents gushing through two narrow coastal gorges. Massive tidal movements create a waterfall effect as water banks up against one side of the narrow cliff passage, which is repeated again and again each time the tide turns.
The twin gaps are part of the McLarty Ranges, which have two ridges running parallel approximately XXX metres apart. The first and most seaward gap is about YY metres wide and the second, most spectacular, gap is about ZZ metres wide. The walls descend a further 46 metres below the surface of the water. The wide gap is capable of moving over 1,000,000 litres through it in one second!
The tides in this area have a 10 metre variation which occurs over six and a half hours from low tide to high tide. The effect of the waterfalls is created by the tide building up in front of the gaps faster than it can flow through them and there can be a four metre high waterfall between the bays.
On a slack tide it is possible to navigate boats through the two gaps to the bay behind, this is best done through a tour but it can be done on private vessels if you are lucky enough to have the qualifications, skill and a suitable vessel. Click here to check tide times at Derby
Access is usually from Derby and Broome but there are a few other towns and remote settlements from which access is possible, flights over the falls are also available BUT will not be sufficient to answer the EC questions.
When it came to todays Earth Science lesson we had two choices, to focus on the tides or the ranges, we chose the ranges as we found them most interesting.
In short, Continental collisions formed the McLarty ranges approximately 1.8 Billion years ago. These ranges were eroded by water, creating sedimentary deposits. Volcanic activity pushed lava and magma into cracks in the deposits of sandstone, forming crystallised quartz, giving the ranges their unique make up, they are comprised of sandstone, quartzite, siltstone, shale and dolomite, uniquely there are abundant stromatolites her too!. Copper is prevalent in the area; surprisingly mining will commence nearby shortly.
To fully appreciate the McLarty ranges its important to look at the Kimberly in a bigger picture. The following information has been used with permission from Dr. A. (Sandy) Scott who presented an illustrated talk to the Kimberley Society.
The Kimberley coast has a rocky shoreline which is segmented into a series of bays, basins, islands and estuaries that have formed on the edge of the Kimberley Plateau. Most of the major landforms are circled by cliffs, rounded headlands and promontories with a lesser proportion of small beaches of boulders or sand and estuary mud flats mostly covered with mangrove communities.
Talbot Bay and the Yampi Peninsula. has been formed from rock formations of the Kimberley Basin but here rock folding has altered their orientation from nearly horizontal to folds with wave lengths varying from a few metres to kilometres and producing in places strata tilted with nearly vertical orientation. One major folding event occurred 540 million years ago and since then ongoing weathering and erosion have reduced the high mountains to plateaus, ridges and valleys. The ridges represent the stumps of the more resistant formations (King Leopold Sandstone, Warton Sandstone and Pentecost Sandstone) and the valleys, now flooded with sea water, have been formed where the less resistant formations (Carson Volcanics and Elgee Siltstone) once existed.
At the Horizontal Waterfalls, an interesting attraction found deep in Talbot Bay, intense folding has tilted the originally horizontal formations through 85 degrees. Stream weathering in the past cut down through joints in the near vertical strata forming gaps in the outer two ridges as water flowed out to sea through a valley in Talbot Bay. At this time the stream may have had to run across the continental shelf for many tens of kilometres westward of Yampi Peninsula to reach the sea. This stream allowed for the weathering and erosion of the two embayments we now see inside the gaps where the two more easily weathered, ‘weak’ formations were once found. The first gap is through a ridge of Pentecost Sandstone that separates Talbot Bay from the first embayment, the second gap is through a ridge of Warton Sandstone and it connects the two embayments. McLarty Range forms the innermost ridge and it is formed of King Leopold Sandstone. Prior to their weathering and erosion, Carson Volcanics occupied the second embayment and Elgee Siltstone occupied the first embayment and remnants of these rocks may still be found on the walls of each embayment.
To log this Earth Cache we require you to visit GZ by Boat and make some observations, consider the information given, then message us with the following answers to the best of your ability;
1. Whilst you whizz through the falls, use your own judgment to fill in the values of XXX, YY and ZZ.
The twin gaps are part of the McLarty Ranges, which have two ridges running parallel approximately XXX metres apart. The first and most seaward gap is about YY metres wide and the second, most spectacular, gap is about ZZ metres wide. The walls descend a further 46 metres below the surface of the water. The wide gap is capable of moving over 1,000,000 litres through it in one second!
2. Can you see any layering in the gorge walls? Are the layers stained a distinct colour? What are these colours and what do think has caused the colours to be there?
3. Identify one rock type present in the Falls wall, describe it?
4. A photo of course, although this task is optional I’ll be disappointed not to see photos of this magical, crazy place!
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 1 week. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted without notice.
Source: kimberley-australia.com, kimberleysociety.org
