Stratigraphic constraints on the timing and emplacement of the Alika 2 giant Hawaiian submarine landslide

Previous work has found evidence for giant tsunami waves that impacted the coasts of Lanai, Molokai and other southern Hawaiian Islands, tentatively d ated at 100 + and 200 + ka by U-series methods on uplifted coral clasts. Se afloor imaging and related work off Hawaii Island has suggested the Alika p hase 2 debris avalanche as the source of the similar to 100 ka "giant wave deposits", although its precise age has been elusive. More recently, a basa ltic sand bed in ODP site 842 (similar to 300 km west of Hawaii) estimated at 100 +/- 20 ka has been suggested to correlate with this or another large Hawaiian landslide. Our approach to the timing and linkage of giant submar ine landslides and paleo-tsunami deposits is a derailed stratigraphic sun e y of pelagic deposits proximal to the landslide feature, beginning with a s uite of seven piston, gravity and box cores collected in the vicinity of th e Alika 2 slides. We used U-series dating techniques, including excess Th-2 30 and Pb-210 profiling, high-resolution paleomagnetic stratigraphy, includ ing continuous, U-channel analysis, delta(18)O stratigraphy, visual and X-r ay sediment lithology, and the petrology and geochemistry of the included t urbidites and ash layers. Minimum ages for the Alika phase 2a slide from de tailed investigation of two of the cores are 112 +/- 15 ka and 125 +/- 24 k a (2 sigma) based on excess Th-230 dating. A less precise age for the Alika phase 1 and/or South Kona slide is 242 +/- 80 lia (2 sigma), consistent wi th previous geological estimates. Oxygen isotope analyses of entrained plan ktonic foraminifera better constrain the Alika phase 2a maximum age at 127 +/- 5 ka, which corresponds to the beginning of the stage 5e interglacial p eriod. It is proposed that triggering of these giant landslides may be rela ted to climate change when wetter periods increase the possibility of groun dwater intrusion and consequent phreatomagmatic eruptions of shallow magma chambers. Our study indicates the contemporaneity of the Alika giant submar ine landslides and distal deposits from enormous turbidity currents as well as coral clasts reported to be tsunami deposits on Lanai and Molokai throu gh direct dating and compositional analysis of the landslide deposits. (C) 1999 Elsevier Science B.V. All rights reserved.