The forces of the sea form the sea-caves, waves seething at the rock face of a coastline, sometimes produce huge caverns, which are typically not very long. They are as long as the water reaches. The existence of this caves is not dependent on the kind of rock. Of course, it helps if the rock is weaker.
Typically sea caves are formed using a weakness in the rocks, like faults, other sediments or weaker layers. Faults in the rock sometimes produce chains of caves; everywhere the fault reaches the seashore.
The coastal erosion opens already existing caves and the water starts to widen the cave. Typically those caves are karst caves. Many karst areas at the coast have caves opening to the sea, where the entrance is widened by the waves. They are often called sea caves, which is only partly true.
Sometimes faults, existing caves or weaknesses in the rock produce a small hole to the surface. The water swashing into the sea caves build up a high pressure inside the cave, which emerges in form of water and air of the small hole. This is called a blowhole. They are found all over the world along the coasts.
The biggest sea cave of the world is Painted Cave on an island belonging to California, U.S.A. The island, called Santa Cruz Island belongs to the Channel Islands National Park. The cave is 402 meters long.
Sea caves are formed by the power of the ocean attacking zones of weakness in coastal sea 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 inter-bedded 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. The cave may begin as a very narrow crack into which waves can penetrate and exert tremendous force, cracking the rock from within. 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. 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 (Washington, Oregon, and California, and especially, California's Channel Islands); the Na Pali coast of Kauai; the Greek Isles; and many other places with good solid rock to host the caves.
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 or 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 deposit. On the right is a sea cave floored with just sand, having emptied out at low tide. Colorful marine algae 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 tide pools, such as anemones,
starfish, and sponges, sea caves with dark zones may harbor organisms not commonly seen. In California, the Giant Anemone is normally green because of algae that live inside of it; but in sea caves with dark zones, these anemones may be white because the green algae don’t get enough sunlight to grow.
Famous Sea Caves
Famous sea caves include the Blue Grotto of Capri, 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.
Sea Caves - Painted Cave
Painted Cave, so called because of its colorful rocks, lichens, and algae, is the longest sea cave in the world. Unfortunately it is rather difficult to visit this cave, as there are no regular tours or boat trips. The cave belongs to the Channel Islands National Park and it is allowed to visit it. Of course it is recommended to talk to the rangers first.
It is also possible to kayak to the cave, but it is not recommended. The water currents and waves are rather difficult and the advice of the rangers must be obeyed.
Sea Caves - Merlin Cave
Tintagel Castle is, according to Geoffrey of Monmouth in his History of the Kings of Britain, written 1139, the birthplace of King Arthur, son of Uther Pendragon and Queen Igraine. But this is just legend. There is no evidence to either prove or disprove this story.
According to the archaeologists, this place was a Roman settlement and military outpost, most likely called Durocornovium.
There was some kind of monastic settlement here in the 5th or 6th century, maybe the stronghold of a Celtic king. This would seem entirely possible, as the site would have made an impressive fort and would be almost impenetrable to any enemies attempting to storm the headland.
A finding during a 1998 excavation increased the possibility of a connection with King Arthur: a slate of 20 by 30 cm with the inscription ARTOGNOV, the Latin version of the British name Arthnou. It’s from the 6th century, which is most likely the time when Arthur lived.
This castle fits the legend very well, because of another fact: Merlin's Cave below the castle. Merlin is said to have lived in a cave below the fortress of Tintagel while King Arthur grew up, to be his teacher. In one version of the legend, Merlin found Arthur washed ashore in a cave below the castle.
Below Tintagel Castle a fault or a layer of weaker rocks crosses the Tintagel Head, the castle is built on. It also crosses several other heads to the north and south, as can be seen from the castle. The rocks were eroded by the sea so several irregular sea caves were formed, all in one row.
Two caves are easy to access from the footpath to Tintagel Castle. Both are high enough to walk through, both are going through the whole head to the other side.
Sea Caves - Grotta Azzurra
The Grotta Azzurra is one of the most famous caves of the world! And the reason why it is famous, led to its today name: the blue light shining through the salt water of the Mediterranean Sea and filling the cave with blue reflections.
So the cave is called Grotta Azzurra, which means Blue Grotto. Once, the locals called Grotta Azzurra Gradola after the nearby landing place of Gradola. It was said to be inhabited by witches and monsters and was avoided.
But the cave was well known much earlier by the Romans, as proved by antique statues found in the Grotto. This discovery, the remains of an ancient landing place and the work on an underground tunnel, creates an image of a natural cavern adorned by statues: a nymphaeum built around the intense and brilliant blue of the sea.
Swimming into the grotto is a unique experience. But it is only possible when no boats with visitors are frequenting the cave.
In summer this is just early in the morning and in the late afternoon. Unfortunately this time is not very good concerning the light. The blue color is best, when sunlight shines on the water in front of the cave entrance.
If you visit the cave by boat, you have to lie down on the bottom of it - in order to fit through the narrow natural opening.
The ceiling is hardly high enough to allow the low boats to enter. The waves of the sea make this a bit tricky; the gondolier has to wait for the lowest water between two waves to enter the cave. Then he hurries to drag the boat into the cave on a rope along the wall.
This situation restricts the access to the cave. Boat tours are only possible with calm sea. High waves, which are even with good weather possible, make the cave visit impossible. But cloudy weather is also a drawback. No sun on the water means no blue light in the cave. So the boats will not enter the cave is one of those weather situations takes place. Please consider this when planning a trip to the cave.
Sea Caves - Sea Lion Caves
As the name Sea Lion Caves says, this cave is used by the Sea Lions. The cave itself is a huge sea cave at the dramatic Oregon coastline. In the Sea Lion Caves region lives a herd of 200 Northern sea lions or Steller sea lions.
Steller sea lions are named after Georg Wilhelm Steller, a German naturalist, who accompanied the Russian explorer Vitus Bering in 1741 on his second Alaskan expedition. Steller was the first who studied and classified these animals.
Sea Caves for Seals
It is the use that grey seals make of the remote and extremely exposed sea-caves of Cornwall, Devonshire and Lundy, which makes their lives uniquely different from nearly all other seals of any species living along the margins of any of the world’s oceans.
Even among the grey seals, only very few breed in sea-caves. At the northernmost sites, they breed on the ice. Elsewhere, they breed on remote or uninhabited islands, usually above the high-water mark and beyond the reach of the waves. In such places, the grey seal pups remain largely untroubled by the sea. Only after weaning, the first moult and a brief period of starvation do they venture into the marine environment.
The atmosphere of the sea-caves is entirely primaeval. Most of the sea-caves used by the seals remain inaccessible to man even in moderate sea conditions. Typically, all have deepwater entrances. The waters in the cave entrance are almost always unquiet, as where the sea funnels into the cave entrance, it piles up and quickens between the walls. From outside, it is possible to peer into the gloom of the cave and glimpse or hear the breaking of the cave wave as it turns to surf around some invisible obstacle or upon the beach within.
Then, to venture as a human being into the cave, hurried in by the gathering wave, spilled with the broken water upon the unseen obstruction or upon a shore as yet unknown, can be a fearful time. It recalls something of the atmosphere and the fears, which must have become familiar to our aboriginal ancestors. Fear of the dark. Fear of what the dark might contain, of being trapped by the rising tide, that the waves may increase in size and intensity, of trapping a limb among large, unstable boulders. It is all written indelibly on the subconscious. In the sea-caves, the lettering becomes luminous. In order to study grey seals in such an environment, it is necessary to confirm which sites they use. This might be achieved by seeing them there, by hearing the eerie ululations emanating from the dark mouth of the cave, by seeing their distinctive tracks in the sand or gravel. It is even possible to smell where they have been, a musky, fishy scent lingering for a while after they have abandoned a sea-cave beach. It is essential, therefore, to where sea-caves were found to be used by seals, accurate measurements informed plan views of the cave, with the reach of water at high and low tide being included. In addition, the extent of all bedrock, sand, shingle and boulders was measured, as were the size and depth of all waters within the cave.
This included the reach of the sea at low tide as well as the location and dimensions of any landlocked pools left by the ebb-tide. The height and nature of any potentially awkward obstacles had to be described. At those caves subject to regular scrutiny, the plan view was measured and redrawn at monthly intervals.
These measurements proved conclusively that the substratum the sea-cave floor was highly mobile. Greatest changes would occur at times when heavy seas were running. A boulder beach might become a sandy beach overnight while a landlocked pool might shrink to one half of its former length and one third of its former depth. Such changes would have important implications for the seals, rendering a cave more or less accessible by humans and their dogs, and therefore unattractive to the seals.
There are also important implications for the observer. It is a habit of grey seal bulls, at certain sites during the breeding season, to rest on the bottom of a sea-cave pool. At no other time have they been found to exhibit this behaviour. The eyes of the bull are open, ever watchful. At such times it is rather like discovering a submarine.
A stealthy approach requires that boulders and cubby-holes serve as places of concealment and, where there is no hiding-place, movement be in a prone position along the base of the cave wall. It is essential to appear as little like a human being as possible and to be mindful of the excellence of their senses of smell and of hearing.
In the sea-caves, an interesting web of sounds exists, chief among which are those of the sea, of surf breaking around boulders, racing across the beach or thundering against a wall of rock. Fresh water may drip from the roof into a pool.
Questing rock pipits call as they hit between boulders inside the cave entrance where they forage for food. Nesting shags, feral pigeons, swallows, martins, kestrels and even peregrine falcons all have their voices. There are the sounds the seals make: punctuated breathing, reminiscent of scuba divers, the snoring of the sleepers, a lone and eerie moaning made by one seal toward that other who drew too close, the thin whine of a hungry pup and perhaps a snarl, uttered in threat or fear.