About the area
Diamond Head is located in the Crowdy Bay National Park. It is located within the Lorne Basin, a 1000 km2 area of sedimentary rocks which were deposited on land during the Early Triassic period. The uniqueness of the rugged headland is a result of a series of lavas which flowed across the area in the Late Triassic. The lavas were altered by fluids which modified the original minerals, and added quartz, pyrite and a little gold to the rocks. The alteration process formed areas of relatively hard, quartz-rich rock which armoured the headland against erosion.
The quartz-rich rocks also contain an abundance of small, perfectly formed, clear quartz crystals whose diamond-like appearance resulted in the geographic name for the site. Following the eruption and alteration of the lavas, magma continued to move upward through the rocks, forming small intrusions and numerous dykes. The combination of lavas, abundant small intrusions and extensive alteration is indicative that this area was on the very edge of a significant volcanic vent.
About the arch
Sea arches are classed as natural bridges and are formed by a process of land, wind or water erosion.
Arches are made where there are two different types of rock, if the bottom layer of rock is softer than the top then it can be eroded over time to form a small crack or cave, this erosion continues and once it has worn all the way through the rock forms a small arch.
The stages of arches development are below.
At the posted coordinates you will be able to find a sign, this sign will give you some more information to assist you in answering the following questions.
The best option is to send us a message via the message centre or contact us via our profile and email with the answers. Please send your answers within 24 hours of logging your visit, we will contact you if there are any issues.
1. Utilising the chart above describe what stage you think this Arch is in? Explain your answer.
2. Estimate the thickness of the roof of the arch and what type of rock do you think it is?.
3. As time goes by and the arch reaches the Destructive Phase the roof will collapse, if a separate column is left what is the correct term for this?
4. OPTIONAL QUESTION -At the posted location you will find a sign, it explains that the area is composed mainly of sedimentary rocks. How many million years old are these?
5. OPTIONAL TASK, please take a photo of yourself in the area with some of the local geology in the background.
References:
Cartoscope, Dr. N.M. Vickery (Nancy) and Mr. R.E. Brown (Bob).
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Did you know, New South Wales has a geocaching association?
Geocaching NSW aims to enhance and improve the activity of geocaching and holds regular events where geocachers meet to enjoy their common interests.
Visit the association website.
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