Once you have meandered your way along the sands of Laguna Beach, you will find yourself at the posted coordinates! Once here you'll notice several sandstone protrustions jutting from the beach into the ocean. These rocks form the basis for marine tidal pools, while in the area please ensure that as you explore you WALK ONLY ON THE DRY EXPOSED ROCK. This will help protect the creatures living within this delicate ecosystem. Please note you do not have to leave the beach to get the answers to this earth cache, however you may be interested in exploring once you get here.
The sandstone protrusions at this area sport a geological feature unique to soft stones in the maritime environment. Honeycomb weathering, also known as fretting, is a form of salt weathering common on coastal and semi-arid granites, sandstones and limestones. The rate of erosion can be as fast as several centimeters in 100 years. Honeycomb weathering occurs throughout the world from the polar regions to the equator. It produces pits in the weathered material, from which it derives its name.
For honeycomb weathering to occur, research indicates that a source of salt is required as the basic mechanism for this kind of weathering is salt heaving. Salt heaving occurs as salt is deposited on the surface of the rock by saltwater spray or by wind. Moisture must be present to allow the salt to settle on the rocks so that as the salt solution evaporates the salt begins to crystallize within the naturally occuring pore-spaces of the rock. Permeable rock such as sandstone or limestone is required so that there are pore-spaces for the salt to crystallize within. These salt crystals pry apart the mineral grains, leaving them vulnerable to other forms of weathering. It takes prolonged periods for this weathering to become visible, as the rock goes through cycles of wetting and drying.
Intertidal honeycomb weathering is found on horizontal planes in rock within the tidal zone. This type of honeycomb weathering is limited in its growth by the rate of evaporation from the sun. Once the depressions have grown large enough that the sun can not evaporate all of the water left in the gap by the retreating wave, the holes are as large as they will get, because the salt can not dry out and wedge grains apart any longer.
HOW TO LOG THIS GEOCACHE: Please use the message system to send the answers to the following questions to the CO. You do not need to wait for a response from me to log your smiley. If I find errors with your answers, I will email you directly and we can discuss how you came to reach your answers. As with all my Earthcaches; if I fail to receive answers, I reserve the right to delete your log without notice! (Though I will always make an effort to discuss with you first!)
1) At the posted coordinates look for some examples of honeycombing in the sandstone. Approximately how wide in diameter are the eroded portions of the rock?
2) In your own words (using the information you've learned in the above lesson) tell me if you think that honeycombing at Laguna Beach has reached it's final state. In other words, can the honeycombs that already exist get any deeper? Why or why not?
3) (OPTIONAL) Take a photo of yourself or your geocaching crew at the GZ. Please try not to include any evidence of the weathering process in your picture to preserve the novelty of the earthcache for future seekers.
OTHER EARTHCACHES BY STNolan:
1) GC5TFRE: The Ross Sea Earth Cache
2) GC6J68X: The Hood Canal Watershed Earthcache
3) GC62H9E: The DC Bioretention Cells
4) GC6QZEK: Lava Dams of the Grand Canyon Earthcache
CONGRATULATIONS TO ckm8dude ON THE FIRST TO FIND!
Sources
Mustoe, G.E., 1982, The Origin of Honeycomb Weathering, Geological Society of America Bulletin, v.93, p. 108-115.
Cache placed with permission of the Laguna Beach City Council Public Works Department (Permitting Office)