South Padre: Barrier Island, Seashells, and More EarthCache
South Padre: Barrier Island, Seashells, and More
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This is not your typical geocache; it is an EarthCache. Instead of looking for a " cache container" you will be brought to a geological feature.
ABOUT THIS LOCATION This EarthCache is along the shoreline on the beach near the Coastal Sudies Lab in Isla Blanca Park. Entrance fee per vehicle $12.00 park hours have been 6 am to 11 pm. Note: you may visit the beach on the gulf side at other places instead. GEOLOGICAL INFORMATION South Padre Island is a typical long and narrow barrier island with a sandy beach gulf side on the Gulf of Mexico, tidal/mud flats on the bay side of Laguna Madre, and sand dunes between them. Except for those sand dunes the Pleistocene Coastal Plain is very flat and extends westward from here over fifty miles. The coastal plain dips, however, about five feet per mile towards the gulf. GEOLOGISTS debate how barrier islands form, but several factors are important such as the variation in sea level. The sea level was between 300 and 450 feet lower when the vast ice sheets held in ice form a good portion of earth's water. Thus, the coast of Texas 18,000 years ago was about 50 miles eastward. This helped create parallel sand bars and barrier islands which still exist submerged many miles out in the present Gulf of Mexico. Brought here initially by the Rio Grande, this enormous amount of sand was another factor in barrier island formation. Waves washed up some of that sand and deposited it on an ever higher feature which eventually emerged from the gulf to form a barrier island. By about 3,000 years ago, well after the glaciers melted and the sea level returned to today's level, this barrier island was forming along the gulf coast. The interaction of sea level, waves, sand, and time becomes apparent in the barrier island formation process. PADRE Island, consisting of South Padre Island and North Padre Island, is one of the longest barrier islands in the world, and at 113 miles long, in the United States it is the longest single barrier island. Likewise, its Laguna Madre is one of the world's largest such lagoons. The two and one-half mile long bridge called the Queen Isabella Causeway crosses the Laguna Madre. The bayside shoreline area can be viewed at various places on the island. One such place is a boardwalk that goes under the bridge near the barrier island. These barrier islands experience what is called longshore drift. South Padre has the general wind/wave trend of southeast toward northwest; this causes the sand here to move alongshore in a northward direction. From about Andy Bowie Park south the beach is not entirely natural, however, due to sand deposition/nourishment from the annual dredging done here. THE beach noticeably has one area with more of a slope or grade while the other part is more level. The former is called the foreshore where the waves wash up and retreat on this seaward sloping area. The latter is called the backshore; this is where the dry sand is that becomes the source for sand dune development. Also, some beach areas will have a similarity to what is called deflation lag. This is where the wind blew away the sand and left the seashells. Don't forget to visit the Coastal Studies Lab with its fine seashell collection and much more. EARTHCACHE INFORMATION Bring your camera and compass. To receive credit for this EarthCache please do the following: 1. Take a photo with your GPS (of you/group if possible) at the beach site. Take a similar photo at bayside site. Send them with log-in. Note: as of 1/1/11 photos are optional, but appreciated. 2. E-mail to me answers to the following: At the beach shoreline the elevation is _____. The wind/waves are coming from _______ direction causing the sand to move in a _______ direction. Do you see an area like a deflation lag here? Are they dredging? The tallest sand dune I noticed is about _____ feet high. 3a. Briefly state three differences between the beach and bayside shoreline areas. 3b. State one reason why you think one of these differences occurs. 3c. Provide location AND coordinates for the site of your bayside observations. You do NOT need to wait for confirmation from me before logging your find. Please do not make any reference to these answers in your log.
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