Welcome to Minjerribah, or Stradbroke Island as it's also known. If you're looking to log this cache you have found your way to the ominously named Deadman's Beach. The history behind the name can be found on a panel on the way from the car park, I won't go into it here because this is a Geology lesson not a History lesson.
There is a chance you will get sandy and wet when doing the steps for this Earth Cache. Please adjust your attire accordingly. And don't forget to slip, slop, slap even if it's cloudy! (See here if this instruction makes no sense: https://www.cancer.org.au/preventing-cancer/sun-protection/campaigns-and-events/slip-slop-slap-seek-slide.html)
Steps to log this Earth Cache
Please message the observations and question answers from the following steps, don't include the answers in your log. Feel free to include your photo from step 5 in the log along with your comments about your Straddie experience. Once you've sent me a message go ahead and submit the log, I'll follow up if there is anything to clarify . There is some brief, but pertinent information below and some links to relevant sources and recent news items at the time of writing (January 2020).
1. From the posted cooordinates take a walk along the high tide line and have a look in the debris for some pebbles/rocks/lumps. If the high tide yields nothing, walk along just below the grass line.
Describe the the colour, shape, texture, distinct features and size of the rocks today (they can vary greatly, for an ideal answer comment on the variances).
2. These rocks are called pumice stone. Some days you will see more than others. What do you think might influence the amount of pumice stone on the beach today? (Use the marterial on this page and the reference links if you're not entirely sure).
3. Pick up some of the pumice. Using the rocks or pebbles you might see in a garden as a benchmark for average, what do you observe about the density of the rock. Why do you think the rock is more or less dense than average? (For an ideal answer include what you've learned about how pumice stone is formed).
4. Put the pumice you've picked up in the water. What happens?
5. Take a picture to show that you've visited Deadman's Beach and post it (or just send it along with the other answers if you'd prefer it not to be in the log)
About Pumice Stone
Pumice stone is an igneous rock which is unique in nature. It is formed when hot rock rich in gas cools in water without the opportunity to crystallise. So it comes from underwater volcanoes and is made from volcanic glass, despite looking nothing like it. Because of the way the rock is formed it is lightweight and porous. It's commercial uses include building materials and abrasives such as toothpaste and exfoliant.
Image Credit: Earth and Planetay Science Letters
When an underwater volcano erupts it can result in a pumice raft, with pieces of pumice ranging from dust particles to the size of houses. This is what washes up on the beach. In August 2019 NASA observed a pumice raft the size of Manhattan Islands in the ocean (see picture below). The raft formed when an underwater volcano near Tonga erupted. Three months later in November 2019 I noticed that the pumice on the beach was larger and more abundant than usual - although this may be coincidence as researchers from QUT expect the pumice to arrive in the Great Barrier Reef around February 2020 and bring with it microorganisms that may help with regenerating the reef. Either way pumice stone that you pick up from the ocean is amongst some of the youngest rock on the planet.
Image Credit: NASA Earth Observatory
The pumice that you see here, be it from the eruption near Tonga or somewhere else, was formed in the Ring of Fire or Circum-Pacific Belt, which is a belt of active volcanos and earthquake zones and is found on the edge of the Pacific, Juan de Fuca, Cocos, Indian-Australian, Nazca, North American, and Philippine Tectonic Plates. It is the source of over 450 active volcanos, which makes up 75% of the earth's active volcanos. With so many active volcanos between here and the next land, there's always going to be at least some small pieces of pumice washed ashore on Straddie.
Image Credit: BBC
References and Sources
https://geology.com/rocks/pumice.shtml
https://www.earthmagazine.org/article/mineral-resource-month-pumice-and-pumicite
https://sciencing.com/pumice-formed-5232410.html
https://www.usgs.gov/faqs/what-are-igneous-rocks?qt-news_science_products=0#qt-news_science_products
https://earthobservatory.nasa.gov/images/145490/a-raft-of-rock
https://www.sciencedirect.com/science/article/pii/S0012821X18300876
https://www.sciencealert.com/the-giant-mass-of-pumice-drifting-towards-australia-has-been-traced-to-an-underwater-volcano
https://www.qut.edu.au/news?id=150228
https://www.nationalgeographic.org/encyclopedia/ring-fire
https://www.usgs.gov/faqs/what-ring-fire?qt-news_science_products=0#qt-news_science_products
https://www.usgs.gov/faqs/how-many-active-volcanoes-are-there-earth?qt-news_science_products=0#qt-news_science_products
A great article from QUT about pumice colours: https://www.qut.edu.au/news?id=180013&utm_source=twitter&utm_medium=social