This EarthCache brings you Cape Peron at Rockingham Lakes Regional Park.
Introduction
Today's coastline may appear unchanging – a fixed curved line on a map, but of course, it is forever changing. During the Ice ages of the last few hundred thousand years, this coastline repeatedly migrated back and forth over the coastal plains of Western Australia as the sea level rose and fell.
Belts of sand dune accumulated along this shifting coastline, made mostly of shells and other marine organisms. In time, this lime-rich sand changed to the Tamala Limestone you see around you. It formed prominent parallel ridgelines such as the limestone hills of today’s suburban coastline.
Following the end of the last Ice Age, the sea level rose more than 120 metres. In its wake, many of the old coastal limestone ridgelines were drowned and eroded, transforming into submarine ridges, reefs and island chains. Cape Peron was once one of these limestone islands.
Today's submarine limestone ridges, reefs and islands were once belts of sand dunes that lay along ancient shorelines.
This is a wonderful EarthCache revealing what Cape Peron was like, some 18,000 to 10,000 years ago, and the subsequence years after that until present.
Figure 1: Limestone emerged rocks and islands south of Cape Peron. The photo was taken from the abandoned gun emplacement up on the hill.
How to claim this EarthCache?
Go to the listed coordinates of the EarthCache where the Lookout Point is (as shown in Figure 1). There are four signboards. Use these signboards to answer the questions below.
Send me the following;
1. The text "GC7CRW2 Cape Peron" on the first line.
2. The answers to the following questions;
- Where was the sea level about 18,000 years ago (Last Ice Age)?
- At the end of the Last Ice Age, the sea level was much lower than today and the coastline lay well out to the west. That was about 10,000 years ago. What were Cape Peron and the emerged rocks and islands (shown in Figure 1) then?
- As the sea level rose (about 8,000 years ago), the limestone ridges were drowned and eroded by waves and wind. What happened to Cape Peron and the nearby emerged rocks and islands shown in Figure 1?
- About 5,000 years ago, the island chain sheltered the coast from strong wave action. Some waves, however, passed through breaches in the chain, shifting sand shoreward to form submarine banks. Lines of coastal dunes then built out rapidly over these banks creating a triangular sandy promontory or cusp. What happened to Cape Peron in the last 2,000 years?
3. Provide a photo of yourself or a personal item to prove you have visited the site.*
References
* Effective immediately from 10 June 2019, photo requirements are permitted on EarthCaches. This task is not optional, it is an addition to existing logging tasks! Logs that do not meet all requirements posed will no longer be accepted.
For additional information, visit; Geosociety.org, Geocaching.com Help Center and Geocaching.com Forum.
Finding the answers to an EarthCache can often be challenging, and many people tend to shy away from these caches because of this. However, it is my opinion that geocaching is also meant to be a fun family experience that simply aims to introduce interesting and unique locations such as this one. Flexibility on logging requirements, however, can only be applied if it can be established that you have actually taken the time to visit the site. For this reason, a proper log describing your adventure accompanied by a good number of photos would be much appreciated.