Dynamic Planet, part six
By G.T. Larson
Molokai is well known for its spectacular sea cliffs, the highest on earth, but the event that created these beautiful sheer cliffs also contributed to the largest landslide debris field known on earth (with the Nuuanu slide on Oahu). Rock debris extends north from Molokai and northeast from Oahu over 100 miles across the ocean floor. One block of debris is approximately seven miles long by 15 miles wide and over 6,000 feet high; it is so large that it has been given a name, the Tuscaloosa Seamount. A natural question would be how did all that debris get there? To better understand these events, it is advantageous to examine an earlier, similar, though much smaller event, on the west end of Molokai.
Molokai was created by three volcanoes. The west Molokai volcano came up first and at its highest was probably several thousand feet higher than the present day elevation of 1,381 feet. The east Molokai volcano came up next and grew quite a bit larger, both in area and in height. Its lava flowed west up to and over the remnants of the eastern half of the west Molokai volcano, which formed the plain where now the airport and most of Molokai’s large farms are located. This area is called the Ho`olehua Saddle. The third and youngest volcano is Kauhako crater which built the Kalaupapa peninsula.
As you are traveling west toward Maunaloa, the highway begins to climb a mile or so past the airport. As you ascend, looking north or to the right, you can see a long escarpment called the Hauakea Pali ending at Mo`omomi beach. It is not as pronounced to the south of the road, but is still discernible. The upper slope to the south also exhibits many eroded gullies and large boulders called residual stones, on the surface of and embedded in, deep red dirt, characteristic of most of west end Molokai. This red dirt, called laterite soil, gets its color from the oxidation of black iron oxide into red iron oxide. These gullies and ridges are the remnants of the main caldera of the west Molokai volcano. The Northwest Rift Zone, which created Ilio Point, and the Southwest Rift Zone, which created La`au Point, radiate out from this area indicating the summit. The whole scarp was formed by a large landslide, probably along a northeast to south rift zone, which slid the eastern half of the west Molokai volcano into the ocean before the east Molokai volcano had spread out much.
This land slide event would have almost certainly have happened all at once, causing a huge tsunami which, if there was much of a summit on the east Molokai volcano, would probably have been overtopped. Young Lanai, Maui and still younger Hawaii Island would have also been adversely affected. The western coasts of North, Central, and South America would possibly have seen tsunami effects. But all of this was just a foretaste of what was to come. Until next time, Aloha Ke Akua.