Cape Foulweather EarthCache
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You are standing on a headland of erosion resistant basalt 500 feet above the Pacific Ocean. It cooled from lava that erupted from a crack in the earth over 300 miles inland.
Cape Foulweather is notable as the first promontory on the northwest coast of New Albion (as the area was then known) to be sighted and named by Captain James Cook, while on his third voyage around the world. His March 7, 1778 journal entry reads:
“The land appeared to be of moderate height, diversified with hill and Valley and almost everywhere covered with wood. There was nothing remarkable about it except one hill. At the northern extreme the land formed a point which I called Cape Foulweather from the very bad weather we soon after met with."
There are two types of vulcanicity, intrusive and extrusive or surface vulcanicity. Cape Foulweather is a great spot to view evidence of intrusive activity.
Intrusive vulcanicity refers to magma (molten rock) being forced into the rocks that make up the Earth's crust. It occurs when there are lines of weakness such as faults, joints, or bedding planes in the crust. When magma enters these lines of weakness and it cools and become solid while still underground, different features called plutons are formed. These plutons will be exposed at the surface of land when the overlying rocks are removed after a long time of denudation (laid bare by erosion).
Major features formed by intrusive volcanicity include: batholith, laccolith, dike, pipe and sill.
Below the Cape to the south you can see curving lines of rocks. These are ring dikes created by lava invading a crack in the earth 15 million years ago. Most visible at low tide, these dikes are great examples of intrusive volcanic activity.
Contrasting with the basalt headlands and offshore rocks is the soft sedimentary rock comprising the shoreline immediately south to Devil's Punchbowl headland. The results of erosion include a pocket beach below here. This same erosion is what has left the ring dikes exposed below you.
To log this cache describe in your own words what the ring dikes look like. You'll need to tell whether you think the tide was low or high when taken as this will impact what you see. Also offer a theory as to why the area beneath the Cape shows exposed dikes while the area a little further south is pocket beach. Explore this area a bit and please also email me with your answers to the above.
Additional Hints
(Decrypt)
Rawbl!
Treasures
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