RECENT EMERGED REEF TERRACES OF THE YENKAHE RESURGENT BLOCK, TANNA, VANUATU - IMPLICATIONS FOR VOLCANIC, LANDSLIDE AND TSUNAMI HAZARDS

Emerged reef terraces record the extraordinarily rapid Holocene uplift rate of the fault-bounded Yenkahe resurgent block (YRB), located with in a partially submerged Quaternary caldera on Tanna Island, Vanuatu, southwest Pacific. The presently active volcano, Yasur, is located at the western end of the YRB. Episodic uplift of the YRB is probably ass ociated with the movement of magma below the Yenkahe area. A historica lly recorded uplift at Port Resolution Bay in A.D. 1878 raised the sho reline similar to 15 m. This A.D. 1878 event was accompanied by a loca l earthquake and a tsunami that reached similar to 12 m elevation. Cor al samples from terraces at mean altitudes of 155 m and 15 m above pre sent sea level yield Th-230/U-234 dates of A.D. 1002 +/- 10 and A.D. 1 868 +/- 4, respectively. These ages imply mean uplift of 156 mm/yr for the YRB since A.D. 1002 until A.D,. 1992. This volcanically related u plift occurs within the context of regional uplift of the southern New Hebrides are. The late Holocene uplift rate, similar to 1 mm/yr, was determined from emerged terraces on the north and west coasts of Tanna . There have been several large volcanic eruptions in the geological h istory of Tanna; continued emplacement of magma at shallow levels belo w the YRB poses a possible volcanic hazard to the population there. Nu merous faults in the weakly consolidated YRB strata and relief created by rapid uplift increase the probability of hazards from landslides a nd tsunamis.