Dunes at GTM EarthCache

Dunes at GTM

Welcome to Guana Tolomato Matanzas (GTM), FL!

EarthCache sites adhere to the principles of Leave No Trace outdoor ethics. Please DO NOT disturb dune vegetation or walk in the dunes. It is UNLAWFUL for any person to pick, gather, remove, walk in the dunes, or otherwise disturb the vegetation present on sand dunes, including sea oats.

About the park: The Guana Tolomato Matanzas National Estuarine Research Reserve encompasses approximately 73,352 acres of salt marsh and mangrove tidal wetlands, oyster bars, estuarine lagoons, upland habitat and offshore seas in Northeast Florida. The GTM Reserve is located in the East Florida subregion, south of Jacksonville and sandwiching St. Augustine. It contains the northernmost extent of mangrove habitat on the east coast of the United States, some of the highest dunes in Florida, measuring 30-40 feet, and one of the few remaining "inlets" in northeast Florida not protected by a jetty thus presenting an easy study of what an inlet might have looked like in the past. The coastal waters of the GTM Reserve are also important calving grounds for the endangered Right Whale.

Fees are:$3.00 per vehicle up to 8 people. $1.00 per Pedestrians, Bicyclists, Extra Passengers in vehicle beyond 8 to this area of the GMT recreation. The Reserve is open all year. The hiking trails are opened from 8:00 AM to SUNSET.

Recreational Activities that can be enjoyed at the GMT

• Beach-going.
• Bicycling.
• Birding and other wildlife viewing.
• Boating.
• Camping.
• Canoeing/kayaking.
• Fishing.
• Hiking.
• Horseback riding.
• Picnicking.

While at GMT you will be either on marked trails (please stay in them) or crossing Highway A1A (be careful!). You will be going on a walking journey to the northern Dunes at GMT. If you plan to stay in the beach area please read the Beach Etiquette sign located in the parking lot bulletin board. It will inform you about while you're having fun there.

A dune is a hill of sand built by aeolian processes. Aeolian processes is the activity of the winds and it's ability to shape the surface of the Earth. Dunes occur in different forms and sizes, formed by interaction with the wind. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face" in the lee of the wind. The valley or trough between dunes is called a slack. A "dune field" is an area covered by extensive sand dunes.

Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach. In most cases the dunes are important in protecting the land against potential ravages by storm waves from the sea. Although the most widely distributed dunes are those associated with coastal regions, the largest complexes of dunes are found inland in dry regions and associated with ancient lake or sea beds.

Dune Types:

1. Sub-aqueous dunes Sub-aqueous (underwater) dunes form on a bed of sand or gravel under the actions of water flow.
2. Lithified dunes A lithified (consolidated) sand dune is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened.
3. Coastal dunes Dunes form where constructive waves encourage the accumulation of sand, and where prevailing onshore winds blow this sand inland. There need to be obstacles e.g. vegetation, pebbles etc. to trap the moving sand grains. As the sand grains get trapped they start to accumulate, starting dune formation. The wind then starts to affect the mound of sand by eroding sand particles from the windward side and depositing them on the leeward side. Gradually this action causes the dune to "migrate" inland, as it does so it accumulates more and more sand. Dunes provide privacy and shelter from the wind.

Aeolian dune shapes are classified as:

1. Crescentic or Barchan: Crescent-shaped mounds are generally wider than they are long. The slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction, and they also are known as barchans, or transverse dunes.
2. Linear: Straight or slightly sinuous sand ridges typically much longer than they are wide are known as linear dunes. Some linear dunes merge to form Y-shaped compound dunes.
3. Star: Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally.
4. Dome: Oval or circular mounds that generally lack a slipface, dome dunes are rare, and these occur at the far upwind margins of sand seas.
5. Parabolic: U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. The elongated arms are held in place by vegetation.

1. Longitudinal dunes: Longitudinal dunes elongate parallel to the prevailing wind, possibly caused by a larger dune having its smaller sides blown away.
2. Transverse dunes: Transverse dunes are perpendicular to the prevailing wind.
3. Reversing dunes: Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above shapes. These dunes typically have major and minor slipfaces oriented in opposite directions.

Now to test your learning experience:

Stage 1 Dunes. Go to N 30° 06.994 W 081° 20.707 and Answer the following question:

1. Describe the difference from the east and west side of the dunes in terms of slope.
2. Which side is steeper?
3. What type of shape is predominant at the dunes. Crescent/Barchan, Linear, Star, Dome or Parabolic?
4. What type of dune formation is predominant here? Longitudinal, Transverse or Reversing?

Stage 2 Near the ocean. Go to N 30° 07.011 W 081° 20.668 and Answer the following question:

1. Using the previously recorded location on stage 1,How far is the top of the dunes from the sea?
2. Estimate How high is the dune?

You are welcome to post photos of your visit to the GTM. Please do not post photos that would give away the answers to any of the educational portion of this cache (stages 1 - 2). Logs with photos that provide the required answers to the questions will be deleted.

Email me the answers to the questions for Stages 1 and 2 to the address on my profile: Click here.

While you are visiting GTM can also get the following caches:

GTM Reserve Cache - GCYQ81

Guana Backwoods - GC1Y6TV

"cache with a view" - GC108NV

Coastal Interdunal Swale at GTM - GC2MYN7

You are encouraged to visit the GTM Research Reserve’s Environmental Education Center to learn more about the Reserve. The center is located at 505 Guana River Road, Ponte Vedra Beach, FL. The center provides a one-of-a-kind opportunity for people of all ages to learn about the many functions of the coastal and estuarine ecosystem and the natural history of Northeast Florida. Staff-led programs are offered to school teachers, students (high school, college, and 7th grade LIFE program with partner schools), adults and environmental professionals. Volunteer-led programs are offered to 4th grade students. Other grade levels can participate on a self-guided visit or a guided tour by a GTM Research Reserve volunteer if available. Other programs at the center include Coastal Science Seminars, brown bag lunch programs on the first Friday of the month, guided walks, and nature movies on the weekends. Please call (904) 823-4500 for a list of special events and guided walks. Admission Fee to the Environmental Education Center is Adults $2.00, Children (10-17) $1.00, Children under 10 - Free. The Center is open from 9:00 AM to 4:00 PM (Closed on state holidays)

Additional websites:

The Friends Of The GTM Reserve

Guana Tolomato Matanzas National Estuarine Research Reserve is part of The National Estuarine Research Reserve System

Sources:

GTM Public Access Map

GTM Website

Wikipedia - Dune

Thanks to Guana Tolomato Matanzas National Estuarine Research Reserve for allowing the placement of this cache.