Microfossil Record of the Tropical Cyclone Pam Deposit from Vanuatu: Implications for Documenting Long-Term Records of South Pacific Storms 

Thomas Jaroslaw Kosciuch1, Jessica Pilarczyk2, Hermann M Fritz3, Isabel Hong2, Ben Horton4, Allan Rarai5, Morris J Harrison5 and Fred R Jockley5, (1)University of Southern Mississippi, Stennis Space Center, MS, United States, (2)Rutgers University, Institute of Marine and Coastal Sciences, New Brunswick, NJ, United States, (3)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (4)Rutgers University, Department of Marine and Coastal Sciences, New Brunswick, NJ, United States, (5)Vanuatu Meteorology and Geo-Hazards Department, Port Vila, Vanuatu
Abstract:
The coastlines of South Pacific Islands are susceptible to inundation by tropical cyclones and tsunamis. Most recently, Tropical Cyclone (TC) Pam (Cat. 5) made landfall on Vanuatu on March 2015 and impacted coastlines of many South Pacific Islands with storm surge heights up to 7 meters above sea level (m.s.l.) and 10-minute sustained wind speeds in excess of 250 km/h. Little is known about events prior to TC Pam, and where present, the event record is fragmentary and limited to only several decades. Geologic studies conducted in coastal areas of other South Pacific Islands have previously revealed evidence of overwash deposits that predate the historical record. These studies provide improved hazard assessment by constraining the possible frequency and magnitude of future events. However, hazard assessment is limited by the difficulty in distinguishing sediments deposited by storms from those deposited by tsunamis. The detailed characterization of a modern analogue, such as TC Pam, is a means of improving our ability to distinguish between storm and tsunami deposition.

We collected a series of modern surface samples from locations within a protected Bay (Undine Bay; 17° 31' 17”S, 168°23’ 51”E) and an exposed beach (Manuro Beach; 17°41’49”S, 168° 35’32”E) on Efate Island, Vanuatu. The surface samples were analyzed for their foraminiferal (taxonomy and taphonomy) content and compared to the foraminiferal assemblages contained within TC Pam sediments at Manuro Beach in order to assess provenance for the sand. Manuro Beach was inundated up to 310 m inland by TC Pam’s storm surge. The TC Pam deposit at Manuro Beach ranges in thickness from 3 to 18 cm and consists of a fine to medium mixed-carbonate sand layer up to 60 m inland. At 60 m inland, the deposit abruptly switches to one consisting exclusively of small, rounded pumice pebbles and extends up to the TC Pam inundation limit at 310 m. Dominant foraminifera within the TC Pam deposit include Amphistegina spp., Calcarina spp., and Marginopora vertebralis, indicating that the majority of the sand was sourced from shallow reefal areas and not from deeper areas offshore.