IDEALIZED CROSS-SECTION OF A TEXAS BARRIER ISLAND
Figure source: UT Marine Research Education
The Texas Coastal Barrier Island system formed about 5000 years ago as the sea level rose after the "Wisconsin" Ice Age covered much of the northern hemisphere with glacial ice. The slowing of this "Holocene" sea level rise in the last 3500 years has established a chain of barrier islands along the Texas, Louisiana, Mississippi, Alabama, and Florida Gulf of Mexico Coasts. The Padre, Mustang, St. Joseph, and Matagorda Island Chain (250 miles) is among the longest barrier island chains on the planet,
From your vantage point here at the Outdoor Classroom, we experience the parts of the island facing the ocean which we commonly refer to as the beach. But the beach has components to consider.
Forebeach and Swash Zone - this is the location where the water laps onto the sloping beachface. Every wave or swash brings in sand and other materials from the ocean. The line of sediment and debris is referred to as the wrack. Look in the wrack for seaweed, manatee grass, and other marine life. Note the amount of plastic debris in our wrack. Plastic pollution is a major problem for our Texas beaches. Can you find a piece of plastic with animal bites? Turtles often mistake floating plastic for jellyfish.
Photo source; Bchrony24
The Berm and Back Beach. The crest of the Forebeach is referred to as the berm and can be a few inches higher than the generally flat and broad back beach area. Note that high tides may flood the entire back beach leaving a wrack of debris near the front of the dunes. Flooding to the dunes is not uncommon and can ruin a beach camping experience. If you are camping on the beach, be sure to ask the rangers about warnings regarding "king," storms, or other high tides.
Activity at this Earthcache: Let's compare the grain sizes of sands we find on the beach in the Forebeach, the Berm, the Backbeach, and at the base of the Dunes. Since much of the sand is fine to very fined grained, this can be a challenge, but you will notice a subtle difference in changing grain size.
Collect a handful of sand from each location: forebeach, berm, backbeach, and base of the dunes - there is a table at the Outdoor Classroom to lay things out for comparison. What do you see?
Put notes about grain sizes and composition into your log.
Hint: Grain size is related to the total energy of wind and wave. How might the energy of the waves change from low tide to high tide? How might storms and wind affect energy on the beach? Where might the highest energy (and largest sand grains) be concentrated? Can you see the subtle differences in grain size?
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Do your part to keep Texas Beaches like Mustang Island clean - grab a bag, help us pick up litter. Pack out more than you bring in. Thank you!
Let us know if you dropped by!