Virtual Field Trip to the Carbonate Sediments of the Florida Keys

Contents of this page: View from Space | Introduction to the Trip | Introduction to the Florida Keys | Start the Trip

Florida peninsula shuttle image

Photograph from space shuttle Discovery. Image and caption information courtesy of NASA.

[Note added February 2003: Many of the images included in NASA's databases were taken by astronauts flying on space shuttle missions. I would like to pay tribute to the huge contribution to the earth sciences made by shuttle astronauts over the years, through the data and images they have gathered. The recent Columbia tragedy illustrates the risks taken by these brave men and women in the cause of science.]

Move the cursor over the image to see an explanation of the features shown.

"Taken during the STS-95 mission from a point over Cuba, this photo shows an oblique, foreshortened view of the Florida Peninsula, with the light blue, shallow seafloor of both the Florida Keys (curving across the bottom of the view) and the Bahama banks (right). 'Popcorn' cumulus cloud covers Miami and the Southern Everglades... Lake Okeechobee is the prominent waterbody in Florida. Cape Canaveral is shown well, half way up the peninsula. Orlando appears as the lighter patch West (left) of Cape Canaveral, near the middle of the peninsula."

Much of the low-lying peninsula is made of Tertiary to recent marine limestones. In the Everglades and the Florida Keys, Pleistocene limestones form the bedrock, which is often exposed at the surface. Modern carbonate sediments form a veneer which is generally a few millimetres to a few metres thick, over the limestone bedrock. Thus, the bedrock plays a strong part in determining the distribution of modern facies.

Florida Keys shuttle image South Florida image map location 12 - Saddlebunch Keys location 12 - Saddlebunch Keys location 11 - Middle Torch Key location 9 - Grassy Key location 9 - Grassy Key location 11 - Middle Torch Key location 10 - Bahia Honda Key location 10 - Bahia Honda Key location 8 - Sombrero Reef location 8 - Sombrero Reef location 7 - Sombrero Beach location 7 - Sombrero Beach location 6 - Windley Key Quarries location 6 - Windley Key Quarries location 5 - Long Key location 5 - Long Key location 4 - South Sound Creek location 4 - South Sound Creek location 3 - Molasses Reef location 3 - Molasses Reef location 2 - Grecian Rocks location 2 - Grecian Rocks location 1 - Key Largo Dry Rocks location 1 - Key Largo Dry Rocks

Above is an annotated enlargement from the Space Shuttle image of the Florida Keys above. Image courtesy of NASA.
Approximate positions of numbered locations are shown: click on the number or arrowhead to go to the location.

Introduction to the Virtual Field Trip

The purpose of this virtual field trip is to introduce you to an example of modern subtropical shallow marine and coastal environments, in which calcium carbonate sedimentation is dominant. It is designed to be used by by students of geology, oceanography, physical geography and environmental sciences, and uses images as an important learning tool.

Locations are grouped into five areas: the Upper, Middle and Lower Keys, with side trips to Florida Bay and the Everglades. You may visit the locations in any order. Each location page contains a number of small ('thumbnail') images. To complete the trip, you should visit each of the images from that location. However, for a quicker tour of the main environments and processes, you may concentrate on the highlighted thumbnail images, usually two or three for each location. For each image, there is some accompanying text. You should make notes on the images and text, just as if you were there in the field. Some images have questions for you to think about, to help you to understand what you are observing, and to give you feedback on your observations. Questions are indicated in the web pages as follows:

question mark Where are the Florida Keys?

This web site is still under development, and additional information, images and exercises will be added to it.

A glossary of some of the more commonly used terms is provided.

Introduction to the Florida Keys

Keys thumbnail map Location map of the Florida Keys

Natural features

The Florida Keys are a chain of Pleistocene carbonate islands some 200 km long, which extend from Key Biscayne (south of Miami), in the northeast, to Key West, in the southwest. Modern sediments are almost entirely calcium carbonate.

Keys zones on NASA image

Image courtesy of NASA

There are various ways of subdividing the Keys into physiographic zones. A simple subdivision is:

  1. A reef tract in the SE, which shelves off steeply into the deep water of the Florida Straits. The reef rarely emerges above low-tide mark, so it may not be strictly correct to refer to it as a barrier reef

  2. A back reef lagoon with various carbonate mud and sand facies, on the ocean side of the Keys

  3. The islands of the Keys: exposed Pleistocene limestone, mangrove swamps, beaches and bays

  4. Florida Bay (and Biscayne Bay in the north): this is really part of the back-reef lagoon, but separated from the oceanward part of the lagoon by the islands of the Keys. Predominantly low-energy carbonate muds, with banks and islands of mud emerging above sea level.


The Florida Keys lie in the sub tropics, between 24° 33' north (Key West) and 25° 48' north (Miami). The climate is warm all year round, with most rainfall concentrated between May to October. See climate data for Miami and Key West - note that temperatures are in degrees Fahrenheit, and rainfall in inches. This area is frequently subject to tropical storms and hurricanes from spring to autumn. These very high energy events are responsible for high rates of sediment erosion, transport and deposition, and drastic modification of environments and ecosystems. See, for example, the map of 2001 tropical storms, and the maps for 1998, 1999 and 2000.

question mark How many tropical storm (T.S.) and hurricane (Hur.) events affected the Florida Keys during the years 1998-2001? Make a list of the events and the dates they occurred. Further information:
question mark What were the effects of these events in the Keys? Search the Web for information on one of the hurricanes and its effects.

Human influence

bridges: view from the west end of Bahia Honda Key of the old railroad-road bridge (left) and the new causeway of US1 (right) The islands have been artificially joined by bridges and causeways. These first carried a railroad, destroyed by a hurricane in 1935, and then a road: this is the southernmost part of US Highway 1, known as the Overseas Highway. Places and addresses are conveniently referred to by 'mile markers' - mile marker 0 is in Key West, and mile marker 107 is on the bridge joining Key Largo to the mainland. Locations on the south side of the highway are referred to as ocean side; those to the north, on the edges of Florida Bay, are bay side.

Much of the natural landscape of the Keys has been modified or destroyed by development. In recent years there has been more protection of natural resources, but there are heavy pressures brought about by the main industry of the Keys: tourism. Effects of development and tourism include:

Key Largo sprawl At times, driving along Highway 1, particularly in the Upper Keys, and ignoring the palm trees and other signs of the sub tropics, you could be almost anywhere in suburban North America: the scene is dominated by tacky strip malls, shopping centres, gas stations, billboards, motels, condominiums and other unattractive manifestations of urban sprawl.
Big Pine canoe trip Off the main highway, though, there are still substantial areas of wilderness and semi-wilderness to be explored on foot, by boat, or by snorkelling or diving. Access to the shoreline, much of which is privately owned, can be a problem. It is most easily accessed in the various state parks, which have excellent interpreted walking trails and canoe trails, and organized trips to view the reefs by snorkelling, diving or from a glass-bottomed boat.

Start the Virtual Field Trip

Now proceed to one part of the Keys or to an individual location selected from the list below:

The Upper Keys


The Middle Keys

Note: text for Locations 7 to 12 is incomplete, but all the images are present

The Lower Keys

Florida Bay

The Everglades

Links and further reading

Content and design by Roger Suthren. Last updated 29 March, 2021 13:10