CORRELATION, DISPERSAL, AND PRESENTATION OF THE KAWAKAWA TEPHRA AND OTHER LATE QUATERNARY TEPHRA LAYERS IN THE SOUTHWEST PACIFIC-OCEAN

Voluminous rhyolitic eruptions and prevailing westerly winds have dispersed late Quaternary ash from the Taupo Volcanic Zone (TVZ) of the North Island, New Zealand, across the Southwest Pacific Ocean. We identify the Taupo (1850 C-14 years), Waimihia (3280 yr), Rerewhakaaitu (14 700 yr), and Kawakawa (22 590 yr) Tephra layers in deep ocean cores, mainly on the basis of their stratigraphic position, radiometric age, and glass shard chemistry. Approximately 25 km(3) of Taupo Tephra were dispersed ENE at least 650 km from the TVZ whereas c. 22 km(3) of Waimihia Tephra and c. 14 km(3) of Rerewhakaaitu Tephra travelled over 500 km to the east. In contrast, at least 400 km(3) of Kawakawa Tephra occur out to 1400 km southeast of the TVZ. Such widespread dispersal is not only a function of the size of the Kawakawa eruption, but is also influenced by the strong wind regime during the last glaciation as manifest by high aeolian quartz contents of sediments encasing the tephra. More ash appears to have deposited offshore than is predicted by exponential thinning models. Taupo Tephra, in particular, has a conspicuous second thickness maximum, 660 km from the eruption centre. Dispersal has extended over different depositional settings that have affected the tephra layers. The best preserved deposits are in zones of high sedimentation including channel levees, submarine fans, and boundary current drifts. In contrast, preservation is poor in regions of active currents including the continental shelf, the crest of Chatham Rise, and the foot of Chatham Rise - Hikurangi Plateau where a deep western boundary current is intensified. Primary tephra deposits are also at risk in regions of frequent gravitational mass movement such as offshore Hawke Bay and eastern Bay of Plenty. Further postdepositional modification is by bioturbation, especially where tephra are c. < 1 cm thick; thicker deposits tend to survive, which implies a smothering of the benthic fauna.