Background:
Littoral Caves, commonly called sea caves, are the highlight of this Earthcache. We will use the term "Littoral Caves" in this lesson. Littoral Caves can be found all over the world on coastlines everywhere. Some caves have even formed long ago and have long since been on dry land, because the area was a former coastline. Some of the largest caves can be found on the Western Coast of the US, and the Hawaiian Islands. The caves featured here are beautiful examples of Littoral Caves, and they can be observed throughout the edges of Arch Cove and Cactus Point.
Formation:
Littoral Caves are formed by erosion of the rock caused by the ocean. The constant movement of the waves wears away, channeling through the rock, forming caves and tunnels. Some caves have been formed by other means, such as acidic breakdown, but are not considered Littoral Caves. If water then fills the cavern, Littoral processes may continue the erosion and wear. The caves can form within any of the three (igneous, metamorphic, and sedimentary) types of rock. Usually the first two types of rock are home to larger caves. This is because they are naturally a stronger rock. Thus, sedimentary rock collapses more easily, allowing only smaller caves to develop. The actual formation of the caves can be attributed to weak spots in the rock itself. How do weak spots come to be?
Weak spots in the rocks are usually faults or dikes (dikes are slabs of rock that crack and protrude from a slab of pre-existing rock). In sedimentary rock, weak spots can also be caused by meeting points of rock of different hardness. The erosion process is magnified at the point of weakness because rock is removed at a greater rate. This causes the caves to form. The water works it's way into small cracks and natural fissures and pocket, and slowly erodes the rock. The weak becomes weaker, removing more and more rock along the weak spot(s). Eventually, sizable caves form and may even create tunnels. If the rock is too weak to support itself over the Littoral Cave, it may collapse, causing a Littoral Sinkhole. These sinkholes, if caused while a whole tunnel is present, can even split the small island in half. There is also other forces to create sea caves. Acidic compounds can eat away at rock. Rainwater, slowly but surely, can erode rock, creating tunnels and caves. Lastly, the enlargement of sea caves can be furthered by the presence of living creatures. Sea urchins, for example, drill into the rock, which over time can break off chunks of the stone.
Logging:
To claim this Earthcache, use your new knowledge of Littoral Caves to E-mail with the following:
•The name of this Earthcache on the top line
•Number of people in your group
•Answer to question: If all the rock along this Laguna Beach coastline is the same type (for all intents and purposes), why aren't there caves at every available spot? The waves are constantly hitting all of the shore, so why only certain spots like here?
Sources:
--http://www.lilburnes.org/Students/Caves/sea_caves_ivanna.htm
--http://en.m.wikipedia.org/wiki/Dike_(geology)
--http://en.m.wikipedia.org/wiki/Sea_cave
--http://www.geocaching.com/geocache/GC475MC_bow-of-destiny