Know before you go: Cell service on parts of Virgin Gorda can be spotty. It is recommended that you add this EarthCache to your offline lists on the Geocaching app or utilize a GPSr before finding this cache. The logging tasks for this geocache are accessible by boat (entering/exiting the harbor) or viewing the shoreline from the pier.
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Creation of Virgin Gorda:
Virgin Gorda is situated on the boundary between the Caribbean and North American tectonic plates. The small Caribbean plate originated in the Pacific Ocean and began to drift eastward with the separation of North and South America approximately 170 million years ago. The Caribbean plate began to sink below (subduct) the North American plate around approximately 120 million years ago. A consequence of this process is volcanism. As the North American plate was forced under the Caribbean plate, pressure built up, and magma began to melt beneath the plates. The Puerto Rico-Virgin Island Platform is an arc of volcanoes close to this subduction zone. Periods of uplift and explosive volcanism have led to the creation of the island of Virgin Gorda. The primary types of rock that make up Virgin Gorda are granodiorite and tonalite (volcanically-created igneous rock).Â
Coastal Erosion:
Coasts that are rocky or contain large cliffs often have very obvious features of erosion. Virgin Gorda does contain rocky shorelines. Wave erosion occurs when waves pummel smoothen large rocks and cliffs into pebbles and pebbles into sand. Waves and currents sometimes transport sand away from beaches, moving the coastline farther inland. Wind erosion can also occur on some coasts. Sedimentary rock such as limestone is often more easily eroded than igneous. Aeolian (wind-driven) processes constantly transport dust, sand, and ash from one place to another. These small particles can bombard a soft rock face and erode it.
Udden-Wentworth Scale:
This scale classifies sediment based on grain size. Grain size is the diameter of an individual particle of sediment.
Boulders are classified to be larger than 256 mm (or 10.1 in) in length.
Cobbles are considered to be 64 - 256 mm or (2.5 - 10.1 in) in size.
Sand is characterized by a diameter of 0.25 - 2mm (or 0.010 - 0.079in).
Logging Tasks:
- Looking towards the shoreline, do you observe boulders, cobbles, or sand present on the beach? If there are multiple of these present, describe their location relative to the shore.
- You should notice large rocks present close to the ocean. Describe the color of the rock. How has erosion changed the appearance of these rocks?Â
- Based on what you’ve learned in the description and your observations at the GZ, what type of erosion has mostly impacted the rock formations around the bay?
- As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. You can put this in your log.
Sources:
https://glossary.slb.com/en/terms/u/udden-wentworth_scale#:~:text=A%20grade%20scale%20for%20classifying,%2C%20granules%2C%20sand%20and%20silt.Â
https://education.nationalgeographic.org/resource/erosion/
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