RHEOGENIC CAVES AND CAVERNOUSE STRUCTURES OF KALAUPAPA PENINSULA, MOLOKAI ISLAND, HAWAII, USA: A MARS ANALOG REVISITED

Located at the north base of Hawaii's Molokai Island, celebrated Kalaupapa Peninsula is the tongue-shaped summit exposure of a largely submarine basalt shield volcano, with a surface about 4 km long, 4 km wide at the base and with a maximum height of about 135 m asl. The peninsula is notable for its variety of volcanic features. Some of these are potential analogs of Martian features. 21st Century studies by members and cooperators of the Hawaii Speleological Survey include Kauhako Crater Pit with parameters similar to those of "the Seven Sisters" of Arsia Mons volcano on Mars. Its parameters also are comparable to those of some pit craters on Hualalai, Kilauea and Mauna Loa volcanoes on Hawaii Island which have been proposed as analogs to the Seven Sisters. But unlike these, Kauhako Crater Pit is an open vertical volcanic conduit at the summit of its volcano. Also, extending north from the outer bowl of that crater is an enormous elevated primary lava trench previously described as a collapsed lava tube, and on the eastern flank of the peninsula are two lava tube cave systems. The occurrence of so many potential Martian cavernous analogs in so small an area suggests that summit topography of small Martian shield volcanoes should be examined in detail in search of subsurface voids of potential biological importance.

Other volcanic features of Kalaupapa Peninsula also merit special study for reasons unrelated to Martian analogies. Extending downward from the surface of a drained lava pond within the outer bowl of the crater is a large, complex drain cavern (Keanalele). Although complex in three dimensions it previously was described as a lava tube. Kauhako Crater Pit itself presently is filled with anoxic sulfide-rich water and functions as an alkalinity pump. It has been dived to 123 meters and plumbed to a depth of 248 meters - a depth approaching that of much-studied Zacaton Pit in Mexico, described as a calcareous structure adjacent to basalt. At depth in Kauhako Crater Pit are thick bacterial wall mats and fingers 15 to 20 cm long, beneath which are secondary calcareous deposits. The morphological similarity of Kauhako Crater Pit to Zacaton Pit suggests that the carbonate-basalt interface of the latter should be clarified.