Perth Pinnacles EarthCache
Hidden : 10/5/2014
Difficulty:
2.5 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:

Why travel some 200km North to see the world famous Pinnacles when you can simply travel to exotic Balcatta to see the 'Pinnacles'

The coast of Western Australia, from Shark Bay nearly to Albany, has a near continuous belt of Tamala Limestone (probably more accurately called) aerolian calcarenite - ie. wind blown calcium carbonate - which has been produced by the combination of wind, rain and the cementing agent of calcium.

A set of unique circumstances produced the pinnacles. Firstly the huge sand dunes stabilised. The rains which fell on the dunes leached down through the sand carrying the calcium. This resulted in the lower levels of the dune solidifying into a soft limestone. As this stabilisation occurred a layer of soil formed on top of the dune which allowed plants to grow and further cemented the limestone below. Gradually the lowest layer of soil, which lay between the surface and the limestone, formed into a hard cap which resulted in the old dunes having three levels - a soil and plant level near the surface, a hard cap below the surface, and a thick layer of soft limestone at the bottom of the dune.

Inevitably the roots from the plants on the top level found cracks and broke up the hard cap and the layer of soft limestone. The result was that under a surface covered with plants and soil the pinnacles developed. No one knows for sure how long ago this process occurred. It may have started as long ago as 500 000 years but equally, it may only be a few thousand years old and it may still be continuing today. The Western Australian Museum has opted for some time in the last 80 000 years.

The surface of most of the Pinnacles is covered with hundreds of short fossil root fragments (Rhizoliths). These individual rhizoliths commonly have a sub-millimeter diameter tubular hole down their centers where the actual root was located before rotting or decaying out of the fossil. The outer surface is very irregular being controlled by nearly random fluctuations in the distance of chemical transport and reaction surrounding an individual root. The sands which make up the Pinnacles and the Tamala Limestone (which extends along much of the west coast of Australia) originated as beach sand brought ashore by the waves of the Indian Ocean. The sand grains are composed of both quartz (generally originating by weathering of continental rocks and delivered to the ocean by rivers) and calcite.

The advent of drier weather in the region resulted in the top layer of plants and soil being removed and gradually the pinnacles were exposed so that today they stand like strange sentinels.
 

To log this Earthcache please answer the following questions;

Compulsory tasks:

1) Within the Pinnacles the layering seems to all be on an angle, what is the approximate angle?
2) What can you see fossilized within the pinnacles?
3) What colours can you see within the limestone?
4) At the waypoint (Lone Pinnacle), how tall is this pinnacle?

Optional tasks:

Take a photo of yourself amongst the 'Pinnacles'

In accordance with the guidelines, the procedure for logging an Earthcache is:

  1. Send me the answers.
  2. Log your visit. "People do not need to wait for permission to log your EarthCache."
Please note : You are welcome to log this Earthcache after sending your answers to me. If no answers are received, your log will be deleted. Please be mindful of your logs to ensure there are no spoiler images/answers for the questions above, spoilers will also be removed.

Additional Hints (No hints available.)



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