Geocache Description:

Geology is Everywhere!   Come to Big Stirrup Cay to discover an EarthCache.

Overview

This is an EarthCache and has no physical container.   It is intended that you read the cache description about the geology of Banks and how they offer protection to Great Stirrup Cay.  You then visit the actual location, make observations, and eventually send the cache owner your answers to the questions below.  If you have any questions, please reach out to me.

While it is likely most people who visit this EarthCache will do so via a cruise ship, it can be completed without coming ashore on this private island.   Bahamian law protects public access to the sea and beaches up to the high-water mark. 

Logging Requirements

1. While near the posted coordinates, observe the shoreline and current ocean conditions.  Is it calm and gentle, or are there large, crashing waves?

2. The color of the water can give indications of the water’s depth.  Compare the color of the water visible around you.  What conclusions do you make about the depth of the posted coordinates and the surrounding area?

3. Compare the waves outside the cove hitting the rocks (see the waypoint for the rocks I'm referring to) versus what makes it into the bay.  Explain what you observe here at the day you visit.

4. Using the information provided and in your own words, explain how the shallow banks help dissipate the wave energy.

5. Upload a photo of yourself (or a personal item) from where you made your observations and attach this photo to your log.

The Lesson

Great Stirrup Cay is a small island in the Berry Island chain in the Bahamas.  It generally enjoys calm waters due to a natural geological formation – the Bahama Banks.  The shallow waters of this area are home to one of the few places in the world where rocks are currently forming today.  The growth rate in Bahama banks is believed to be a much as 4.5 inches (or 11.4 centimeters) per 100 years.   As such, this feature is generally referred to as a “Carbonate Factory.”  Carbonate particles are created as organisms absorb and precipitate CaCO3 (calcium carbonate) for their skeletal structure from the seawater. 

This high carbonate production over millions of years has led to a seafloor much higher than normal.  Parts of the Bahamas are covered with these carbonite deposits over 3 miles (or 4.8 km) deep.  Much of the waters around Bahama Banks are shallow – often less than 30 feet (or 9 meters) deep while the surrounding oceanic areas drop off to great depths.  These shallow waters combined with the limestone bank together form a natural breakwater around Great Stirrup Cay and much of the Bahamas.  This sudden shallow depth helps break up large ocean waves or storm surges, causing them to lose significant amounts of energy.  While in the short run the shallowing at a typical beach can lead to higher waves, the extended shallows in the Bahamas tends to lead to the waves being much smaller or almost non-existent on calm days by the time they come ashore.

In the Bahamas (and elsewhere), the color of the water is a key indicator of the likely water depth:

• Dark Blue – deep water, generally over 30 feet (or 10 meters) deep

• Powder Blue/Light Blue – depth is generally 30 feet (or 9 meters) or less

• Green – depth is generally 20 feet (or 6 meters) or less

• Pale/White – very shallow, over sand or sandbars

Overall, the geology around this small cay helps protect it from most of the wave action that islands with deeper offshore depths must face.

Sources:

The Bahama Banks:  A "Living" Fossil-Environment by Louis S Kornicker

Geomorphology of Cay Sal Bank Bahamas – Living Oceans Foundation

Bahama Banks and Florida Platform – by Travelinggeologist.com

How do coral reefs protect lives and property?  - NOAA

Coastal Protection - Coral Reef Alliance

Geological Studies on the Great Bahama Bank - Normal Newell and Keith Rigby

Reading The Water – passagemaker.com

Satellite View of Shore – by Google©