The island of Molokai, a volcanic doublet, is the fifth in size of the islands of the Hawaiian Archipelago, which extends about 2500 km (1554 mi) southeastward across the central Pacific Ocean from Kure on the northwest to Hawaii on the southeast (Fig. 1). The broadly linear chain of islands which make up the archipelago caps the Hawaiian Ridge, a pronounced topographic high on the Hawaiian Swell. The ridge is bordered by the Hawaiian Moat (or Deep) which is in turn bordered by the Hawaiian Arch (or Rise). These three topographic features, the ridge, moat and arch, are superposed on a broad elongate ridge, the Hawaiian Swell (Betz and Hess, 1942; Dietz and Menard, 1953). Dana (1849, 1890) recognized from geomorphic evidence that extinction of the chain progressed from northwest to southeast, and McDougall (1964) confirmed the general progression with K-Ar ages of lavas from Kauai, Oahu, Molokai, Maui and Hawaii. The general progression of ages of the Hawaiian-Emperor chain and its relation to Cenozoic Circumpacific tectonics has been described by Jackson et al. (1972) and Dalrymple et al. (1973). Fiske and Jackson (1972) have investigated the influence of regional structure and local gravitational stresses on the orientation and growth of Hawaiian volcanic rifts. Macdonald and Abbott (1970) give an excellent summary of the geomorphology of the Hawaiian Islands and of the processes that formed, and are continuing to form them. This summary contains a geologic sketch of each of the major windward islands (extending from Kauai to Hawaii) individually, and the leeward islands (extending from Kure to Nihoa) as a group.
