 |
 |
 |
|
Sea caves are formed by the power of the ocean (or in some cases, lakes) attacking zones of weakness in coastal cliffs. The weak zone is usually a fault, or fractured zone formed during slippage. Another type of weak zone is formed where dissimilar types of rocks are interbedded and one is weaker than the other. Typically this is a dike, or intrusive vein of more easily eroded rock found within a stronger host rock. Yet a third instance is in sedimentary rocks where a layer of softer rock is interbedded between harder layers. The cave may begin as a very narrow crack into which waves can penetrate and exert tremendous force, cracking the rock from within by both the weight of the water and by compression of air. Sand and rock carried by waves produce additional erosive power on the cave's walls. Sea caves rarely have formations like solution caves or lava tubes, so we're just devoting one page to them here in The Virtual Cave. Occasionally some flowstone or small stalagmites are seen, formed much as in solution caves. Typically these occur in caves formed in sandstone or basalt. Sea caves are found all over the world, and may be one of the most numerous type of caves. Areas known for large concentrations of sea caves include the Pacific coast states of the USA (Alaska, Washington, Oregon, and California, and especially, California's Channel Islands); the Na Pali coast of Kauai; the Greek Isles; the British Isles, and many other places with good solid rock to host the caves. The author has explored and surveyed over 500 sea caves, and written two books and an encyclopedia chapter on them. Below are a sampling of some of the photos taken along the way. |
 |
The Entrance Zone Sea caves may be explored in several ways: with kayaks or other small boats; by swimming in; or in some caves, by wading or walking if the cave empties out at low tide. When entering a cave where the surf is active, it's best to wear a helmet and study conditions carefully before entering. Remember that the power of waves and swell will be amplified in the cave interior! |
 |
 |
Inside a Sea Cave Inside, a sea cave may be dry or wet, depending on the tide, time of year, or the locale. On the left is a long cave formed along a fault, visible along the sloping wall on the right. The white material on the walls is calcite, deposited by water percolating through the rock.. On the right is a sea cave floored with just sand, having emptied out at low tide. Colorful marine algaes adorn the ceiling.
|
 |
|
|
Life in a Sea Cave Sea caves may abound with life, both on their walls and floors.
Besides the kind of critters seen in normal tidepools, such as anemones,
starfish, and sponges, sea caves with dark zones may harbor organisms
not commonly seen in shallow water. . In California, the Giant Anemone
is normally green because of an algae that lives inside of it; but in
sea caves with dark zones, like the one lower left, these anemones may
be white because the green algae doesn't get enough sunlight to grow.
|
  |
 |
Famous Sea Caves Famous sea caves include the Blue Grotto of Capri (left), and Fingal's Cave on the British island of Staffa (formed in columnar basalt). While spacious inside, they are only moderate in length, neither of them exceeding 250 feet from end to end. |
 |
 |
World's Longest The world's longest known, actively forming sea cave is Painted Cave on California's Santa Cruz Island. It is 1215 feet long and large enough to take a 40-foot boat inside. On the left, looking out the 130-foot-high entrance. On the right are two views of the very dark inner chamber. The bottom image shows a sharp edge to the right of the red kayak, where the two faults along which the chamber eroded intersect. Sea lions inhabit the ledges in the back of the chamber much of the year. Click here to see a detailed map of the cave. Kayak tours to Painted and nearby caves are offered by Paddle
Sports of Santa Barbara
|
  |
 A 50-foot dive boat in the entrance of RikoRiko, viewed from inside and outside (upper right) |
World's Largest When we ask what is the world's largest sea cave by volume rather than horizontal length, we get a different answer: Riko Riko Cave, on the Poor Knight Islands off the east coast of New Zealand's North Island. Lengthwise, Riko tapes out at only about 500 feet, but the egg-shaped chamber was determined via laser survey to have a volume of about 7,800,000 cubic feet. Painted Cave's volume can only be estimated from its survey, to be roughly 56% that of Riko. Dive! Tutakaka offers boat tours of the Poor Knights that include a visit to Riko Riko. Click here for a detailed article on the 3D laser survey of Riko Riko with more photos, in Adobe Acrobat format. |
|
| Back to: | |
 |
Last updated Dec. 12, 2008 |