Turbidites from slope failure on Hawaiian volcanoes

Turbidites are common in the sediments surrounding the Hawaiian Islands. Cores were taken during leg 136 of the Ocean Drilling Program 320 km west of the island of Hawaii on the outer side of the arch that surrounds the southern end of the Hawaiian chain. They contain Pleistocene to late Oligocene graded volcanic sand layers with fresh glass (or its alteration products) and mineral fragments (olivine, plagioclase, and clinopyroxene). Some layers have mixed assemblages of Pleistocene to Eocene radiolarians or Eocene and Cretaceous ichthyoliths. The glass fragments are weakly vesicular and blocky to platy in shape. The glass fragments from individual Pleistocene to Pliocene layers have large compositional ranges (i.e. larger than expected for a single eruption). These features indicate that the turbidites probably were deposited from turbidity currents that originated on the flanks of Hawaiian volcanoes. The low to moderate sulfur content of the sand glasses indicates that they were derived from partially degassed lavas that were erupted under shallow marine to subaerial conditions. The turbidity currents ran over the c. 500 m high Hawaiian Arch, which indicates that the currents were at least 325 m thick. Similar turbidite deposits are located 930 km south of the Hawaiian Islands. Thus, debris avalanche from Hawaiian volcanoes can generate enormous turbidity currents that transport sediments long distances from their source. This phenomenon is an alternative explanation to Antarctic bottom waters for generating mixed assemblages of Pleistocene and Eocene radiolarians in deep-sea sediments.