The steep bedrock exposures and powerful waves of the Southeast Alaskan islands present an ideal setting for the creation of sea caves. These are found in greatest abundance on the exposed side of the outer islands, which receive the full energy of the Pacific Ocean, but are also known from the parts of the Inside Passage. In addition to modern sea caves, there are "raised" sea caves from the early postglacial interval. Sea level rose at the end of the Ice Age as the ice sheets melted, and glaciated areas (such as southeast Alaska) underwent isostatic rebound in the centuries that followed. Most raised sea caves on Prince of Wales Island and the nearby outer islands are about 30 meters above modern sea level and were probably formed around 9,000 years ago. Their position above current sea level protects them from waves, and some contain bones and archaeological remains of considerable antiquity. All such remains are postglacial in age, however.
Puffin Grotto is a spectacular sea cave on the southern side of Cape Addington, Noyes Island (see photos above and at left). It is still being sculptured by the waves, and its lower reaches are filled with modern driftwood. But its upper levels are well above the highest waves, and bird bones left by scavengers are scattered about on the mossy floor. Still farther back, through a crawlway, the cave opens up into a room full of wave-rounded boulders (see photo below). These boulders (made mostly of metamorphic rocks) have been coated by calcite falling from the limestone ceiling, showing that they have not seen waves in thousands of years. Among these boulders cavers located an eroded whale vertebra, which Dr. Heaton collected in 1996. It is the atlas/axis complex of some great whale (baleen or sperm whale). It is associated with fish bone from otter scat that is probably much younger.
This is the only cetacean bone located so far in any Southeast Alaskan cave. It was radiocarbon dated at 5,115 years old. The abraded nature of this bone and its position among rounded cobbles and boulders (see photo below) suggest that it was worked and deposited by waves. Since further wave action would certainly have obliterated this delicate object, its age probably represents the final period during which waves were able to reach this remote upper level of the sea cave.
|Geologist Tom Hamilton emerges into the boulder-filled back room of Puffin Grotto (left). The partial vertebra of a great whale was found located among the boulders and, like them, was probably deposited by ancient waves (right).|
Although the sea caves of Southeast Alaska are spectacular and often contain bones and human artifacts, their limited age keeps them from holding clues to the Ice Age history of the region. During glacial intervals sea level was much lower than it is today, and any sea caves formed during such times are now drowned. Perhaps in the future scientific divers will uncover important sites in such places.