Earth Sciences Lesson: Geological Material
Rottnest Island is characterised by alternating limestone headlands and bays with white sandy beaches, flanked by sand dunes. The Island originated as coastal sand dunes, now cemented into a sedimentary rock called limestone.
Limestone on the Island is broken down into three distinct types:
• Tamala Limestone, oldest dated at 140 000 years.
• Rottnest Limestone, oldest dated at 132 000 years.
• Herschell Limestone, oldest dated at 8 000 years.
This means that Rottnest Island is composed entirely of rocks less than 150 000 years old, which formed during what geologists refer to as the Pleistocene and Holocene epochs.
Rottnest Island is the largest and most northern in a chain of islands. The diagram above shows these islands as emergent features of a limestone ridge that was once part of the mainland before the sea level rose approximately 10 000 years ago. Wind and water continue to shape Rottnest Island today and there is evidence of shoreline movement in many locations. Vegetation stabilises the sand, so if the vegetation is lost there is significant movement of sand, causingdune blowouts.
Further Reading: Guidebook to the Geology of Rottnest Island by Phillip E. Playford.
Questions:
- Looking southeast describe the predominant landform feature of the landscape in two to five words.
Instructions and How to Verify Your Find
Once you complete the “More than a Hill” 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 GC5VB9Z and cache name (More than a hill ) 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.