To Reef or not to Reef? Rottnest Island, Western Australia, Australia
By Rottnest Islander on 11-May-15. Waypoint GA7206

Fairbridge Bluff is a site of international significance due to its unique geological evidence of sea level change and environmental change during the Quaternary. Sea level was at least 3 m higher, and coral reefs grew here.

Earth Sciences Lesson: Geological Material

Rottnest Island water temperatures during autumn and winter are increased significantly (up to 3°C) by the southern flowing Leeuwin Current, which brings warm tropical water over the continental slope and outer shelf.  These warmer waters allow perfect conditions for the growth of coral.

Fairbridge Bluff has evidence of both past and living coral reef communities. Exposed fossilised corals are found above the high- tide mark at Fairbridge Bluff, suggesting sea level would have been three or more metres higher than today, as the coral would have been submerged in a metre of water to have grown to such an extent. As you look out past the breaking waves you’ll notice living coral reef exposed at the low tide - if you have a mask and snorkel it is worth a look.

Just to the west of Fairbridge Bluff the Tamala Limestone contains evidence of ancient tree roots. This evidence extends below the current sea level indicating that it was once significantly lower than today.

Further Reading:

Guidebook to the Geology of Rottnest Island by Phillip E. Playford.

Questions: 

1. In front of you are several solution pipes which are the evidence of tree roots in the Tamala Limestone – please refer to the picture to help you identify them. Count the total number of solution pipes present in the central outcrop of the bay.

Instructions and How to Verify Your Find

Once you complete the “To Reef or not to Reef” EarthCache requirements you can post your find without delay, as per the EarthCache guidelines. You will, however, need to verify your find by sending me a message with the GC code and cache name on the first line and provide your answers to the questions listed below, otherwise your log may be removed.

Adhering to the EarthCache guidelines, please be careful not to include any detail in your log or photos that may assist others in answering the questions without actually visiting the sites and carrying out the fieldwork.

This EarthCache presents a good opportunity to practise CITO (Cache In Trash Out), so please bring a rubbish bag and help save the environment. Take a photo of the rubbish you collect along the way and include in your log for bonus geo-karma points!

Make sure you stick to the designated paths and leave no trace. Please do not interfere with the geological material, vegetation or wildlife – the tasks can be completed without the need to damage the environment.

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