Welcome to Xiaoliuqiu — An Island of Geological Wonder! ((BIO)EROSION)
In this Earth Cache, you will learn about erosion — specifically bioerosion (borings) with a comparison of coastal erosion (potholes), and how these two forces of Mother Nature helped create a one-of-a-kind rock formation right here on the coast of Xiaoliuqiu known as Guanyin Rock, since the rock resembles the face of the Buddhist Goddess, Guanyin. So, upon learning all there is to know about bioerosion and coastal erosion, and the forces of organisms and ocean water that sculpted "Guanyin Rock", you will be ready to put on your Earth Science Caps and get geological on location here at Xiaoliuqiu Island. And after you answer the task questions and complete all your Coastal Erosion Studies and Observations (which can all be found at the bottom of this page), you can log a “Found It!” for this Earth Cache. I hope you enjoy! Are you ready? Let's begin . . .
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What is Bioerosion Exactly and how Does it Compare to Coastal Erosion?
Here at the Posted Coordinates, you will see a "strange" rock formation that seems to be literally standing while all other rocks around it lie flat. This rock is known locally as Guanyin Rock and is the result of bioerosion and coastal erosion. So how did this rock form and why are there so many holes in it? Well, first of all we have to look at Xiaoliuqiu as a whole, especially this area where there is an abundance of coral limestone — rocks consisting of the calcareous skeletons of corals often cemented by calcium carbonate (CaCO₃). In other words, coral limestones are the "homes" of organisms of the past. Because Xiaoliuqiu is a coral island, meaning it formed over millions of years from raising coral reefs, there is evidence of past animal life all over the place, more so here at Guanyin Rock. So, with the presence of any animal life in the area comes the "destruction" of things, namely the coral limestone and this "destruction" is known as bioerosion — the removal and transport of materials by the action of organisms. In other words, animals need homes so they carve out or dig into an area of rock to live in as they did so here at Guanyin Rock as is evidenced by all the holes within this rock. And these holes are known as borings, which were made by sponges and mollusks. Below you can see what the fossils of sponges and mollusks look like:
So, it is evident that sponges and mollusks were once present in and around Guanyin Rock as there are holes everywhere within the rock itself. However, it has also been argued that the holes of Guanyin Rock are a result of coastal erosion — specifically wave abrasion, which resulted in creating these marine potholes. In order for these potholes to have formed, wave abrasion needed to happen — the power of the seawater to create a vortex or a swirling, whirlpool motion to throw around pebbles, which act as a "grinder" to grind out a hole within the depression. And over many, many, many years of this constant swirling around of pebbles and their grinding action, a pothole is formed. And here at Guanyin Rock, it appears that in addition to bioerosion, wave abrasion also played a part in creating the "(w)holy structure."
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Logging Requirements:
Xiaoliuqiu is an island of Geological Wonder with so many unique landforms and hidden geological treasures, with one in particular — Guanyin Stone — which is a place where both bioerosion and coastal erosion took place to shape this unique rock formation.
In order to log a Found It! for this Earth Cache, please go to the Posted Coordinates to complete the following tasks:
1. Based on what you have learned about bioerosion and coastal erosion, and based on your observations of Guanyin Rock, do you find a bigger concentration of borings or potholes? Why do you think this is so? How did you come to your conclusions?
2. Based on what you have learned about the past marine life here of sponges and mollusks, were you able to observe any fossils of these creatures here at Guanyin Rock? Where in relation to the holes in Guanyin Rock were these fossils? What does this tell you about the holes themselves?
3. Based on all your knowledge of bioerosion and coastal erosion, and based on your observations during Tasks 1 and 2, do you feel that Guanyin Rock was shaped because of bioerosion or coastal erosion or both? Or are there any other outside forces that could have contributed to shaping this rock? How did you come to your conclusions?
4. Send a photo to me via the Geocaching Messening Service of what you classified as a pothole vs. what you classified as a boring. How did you come to these conclusions?
5. Optional — Post a photo of yourself or a "Geocaching" item identifying yourself here at "Guanyin Rock."
You may log a Found It! on this cache after you have completed the tasks and emailed me the answers. If there are any issues with your answers, I will contact you. And as a friendly reminder, please do not post any of the answers in your logs. Thank you for visiting this Earth Cache. I hope you enjoy your time here at Guanyin Rock.