An Island of Salt and Pepper EarthCache

SALT DOMES

A salt dome is a type of structural dome formed when a thick bed of evaporite minerals (mainly salt, or halite) found at depth intrudes vertically into surrounding rock strata. Over time, the salt is covered with sediment and becomes buried. Since the density of salt is generally less than that of surrounding material, it has a tendency to move upward toward the surface, forming large bulbous domes, diapirs , sheets, pillars and other structures as it rises. In cross section, these large domes may be anywhere from 1 to 10 kilometers across and extend as far down as 6.5 kilometers. One example of an island formed by a salt dome is Avery Island in Louisiana. At present ocean levels it is no longer surrounded by the sea but it is surrounded by bayous on all sides.

There are over 500 salt domes in the onshore and near offshore part of the northern Gulf Coast region, and others occur in Mexico, Central America, Cuba and under the GOM. Not truly islands, these marvels are elevated mounds surrounded by Holocene coastal marshes.

The five Louisiana islands, arched up by rising salt stocks, are the only large topographic hills in the swamp, marsh and coastal plains of southern Louisiana and were a conscript habitation for prehistoric Indians and later European settlers. Geologists believe these mysterious elevations were created when a saltwater ocean covering what is now Texas, Louisiana and Mississippi evaporated, leaving behind a vast sheet of salt. The salt was formed in a narrow sea that existed during an early stage in the breakup of the supercontinent Pangea, more than 200 million years ago. Over time this salt layer was covered by thousands of feet of alluvial sediment, the pressure of which pushed numerous salt domes straight up.

In five places these domes actually pushed up the topography.Today, these five coastal islands sit above and are surrounded by the drab, yet strangely exquisite swamps and marshes of south Louisiana. The islands (Avery, Weeks, Côte Blanche, Belle Isle and Jefferson) are circular topographic prominences from one to two miles in diameter, rising 75 feet or more above the surrounding marshlands. Avery Island stands the highest at 152 feet above sea level.

History of Avery Island

Long before its namesake Avery family settled there in the 1830s, American Indians discovered that Avery Island’s verdant flora covered a precious natural resource—a massive salt dome. There the Indians boiled the Island’s briny spring water to extract salt, which they traded to other tribes as far away as central Texas, Arkansas, and Ohio.

According to records maintained prior to 1999 in the Southern Historical Collection at University of North Carolina at Chapel Hill,[2] Petite Anse Island, renamed Avery Island in the late 19th century, was purchased by John Craig Marsh of New Jersey in 1818. Besides mining salt, Marsh operated a sugar plantation on the island's fertile soil. A daughter, Sarah Craig Marsh, married Daniel Dudley Avery in 1837, thus uniting the Marsh and Avery families. Daniel Dudley Avery hailed from Baton Rouge, Louisiana, and was a jurist. In 1849, Daniel became co-owner of his inlaw's sugar plantation and salt mines, and in 1855 he became sole owner.

Just prior to the Civil War, Edmund McIlhenny joined the Avery family by wedding Mary Eliza Avery, daughter of Daniel Dudley Avery and Sarah Marsh Avery. After fighting in the Civil War, Edmund McIlhenny returned to his Avery Island plantation to find that not much had survived. The salt works on this Gulf Coast Island were inoperable. The sugarcane fields had been destroyed. But Mr. McIlhenny was delighted to find that the special red peppers he had planted in his garden before the war had miraculously survived. He began to experiment with making pepper sauce, and eventually hit upon a formula that worked by crushing the ripest, reddest peppers, mixing half a cup of local salt with each gallon, then aging the mixture in crockery jars for thirty days. He added fine French wine vinegar, and aged the sauce for another thirty days before straining and bottling it. He chose a Central American Indian name for the product, "Tabasco", and shipped the first batch of 350 bottles in 1868. The hot sauce took off like wildfire, and orders came in faster than they could be filled. Tabasco has since become the definitive seasoning sauce, offering people around the world a taste of south Louisiana. Just a few drops helps to accentuate the flavor in foods. Some folks wouldn't dare eat eggs without a dash of Tabasco and it is a vital additive to many recipes, including Bloody Marys.

To log this earthcache, please do the following:

1. Optional: We recommend that you post a picture with you and/or your GPS in the background with the Jungle Gardens gift shop in the background.

2. Required: Email the cache owner with answers to the following questions:

(A) At what depth was the salt deposit discovered at in 1862?
(B) On what date were the salt works destroyed by the Union Army?
(C) Avery Island reaches a total maximum elevation of 152 feet above sea level. What is the elevation at the listed coordinates? Take an elevation reading from your GPS at the listed coordinates and email it to the cache owner.

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