Seawall Honeycomb Weathering @ Camp Reynolds EarthCache
Hidden : 8/6/2014
Difficulty:
2 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:

My visits to Angel Island always include a trip down to the Seawall at Camp Reynolds. Here I rest my feet, eat my lunch, and take in the spectacular view. Few people seem to venture all the way down to the seawall, which makes it even more special. My hope for this Earthcache is to introduce you to this special place while learning a few things about this old and weathered seawall.

If the tide is high you should still be able to complete the requirements of this Earthcache, however it's much more interesting to inspect the seawall from the beach.

The Camp Reynolds seawall was constructed sometime between 1864 and 1877. The seawall is constructed primarily of sandstone which was removed from Quarry Point at Fort McDowell (on the east side of Angel Island), but also contains some gabbro and granite boulders. As you examine the seawall you’ll observe that the sandstone blocks in the lower part of the seawall do not appear to be experiencing the same honeycomb weathering that you’ll find on the upper portion of the wall. It is believed that the reason for this is that the upper part of the wall is constantly being exposed to damaging saltwater sea spray, while the lower part of the wall is submerged during periods of high tide. As the sea spray evaporates from the seawall, the salt crystallizes within the porous spaces of the permeable rock. These growing crystals pry apart grains of sand which then leaves them vulnerable to other forms of weathering. In just 150 years, this continuous cycle of wetting and drying has resulted in the beautiful honeycomb weathering that you see in the wall today.

As you continue your examination of the seawall you’ll begin to notice the non-sandstone boulders that stand out in the upper portion of the wall due to their lack of weathering, and that the sandstone boulders of the upper wall have eroded as much as 6 to 8 inches. Based on this information we can estimate that the wall is eroding at a rate of approximately one-half inch per decade.

To receive credit for this Earthcache you'll simply need to email me the answer to the questions below. There's no need to wait for approval before logging the Earthcache. I'll let you know if I have any questions. Thanks!

Question 1: In your estimation, how many years will it take for the upper sandstone portions of the seawall to completely erode?
Question 2: Do you think that the damage to the southernmost end of the seawall was caused by honeycomb weathering? If no, then what?

For more information on the fascinating geology of Angel Island, check out: (visit link)

Additional Hints ()

Ahzore bs Lrnef = Jnyy guvpxarff va vapurf / bar-unys vapu k 10 lrnef

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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