Sedimentary record of Cyclone Pam from Vanuatu: implications for long-term cyclone and tsunami records for the South Pacific

Personnel

Investigator: Jessica Pilarczyk
Graduate students: Thomas Kosciuch, Isabel Hong
Collaborators: Hermann Fritz, Ben Horton, Vanuatu Meteorology and Geo-Hazards Department (Rarai, Harrison, Jockley), Davin Wallace, Clayton Dike

Funding

National Science Foundation (NSF) EAR-1545619

Project Summary



On 13 March 2015 Tropical Cyclone (TC) Pam made landfall on Vanuatu (South Pacific) as a Category 5 storm with 10-minute sustained wind speeds as high as 270 km/h and storm surge flow depths as high as 7 m above mean sea level (MSL). TC Pam’s impact resulted in 16 deaths and the displacement of up to 3300 people from their homes. Vanuatu is an archipelago consisting of 82 islands, many of which are isolated and did not receive proper warning of the impending storm. Landfalling Category 5 tropical cyclones are rare. Understanding patterns related to tropical cyclone frequency and intensity is difficult because instrumental records are too short to estimate the potential frequency and intensity of the strongest events, which can occur centuries apart on the same coastline. Scientists circumvent the short instrumental record by examining the long-term geologic record for evidence of past tropical cyclones. Geologic records have produced many reconstructions of landfalling tropical cyclones and can be used to assess the risk of future events. However, a critically important question remains. Can sedimentary deposits be used to assess the intensity of landfalling tropical cyclones? Sediments deposited by landfalling storms address this question because they preserve evidence of past events that have occurred over centennial and millennial timescales. Sedimentological and paleontological proxies provide further information because they indicate how far offshore sediments were transported by storm surge. More intense events are often associated with higher storm surges and are expected to transport large volumes of sediment from deeper environments offshore. Less intense events, with lower transport capacity, are expected to transport less material that is predominantly sourced from closer to shore. However, this can vary from site to site and is dependent on both the sediment available for transport and the bathymetry of the coastal zone. This study presents urgent and perishable data, which was rapidly being lost due to post-depositional change, and provides the first modern survey of an intense (Category 5) tropical cyclone impacting the South Pacific islands. The numerous coastlines that TC Pam impacted span a distance of over 350 km, providing a unique opportunity to assess the environmental impact and associated sedimentary deposit over a large distance. Our study examined the latitudinal changes in TC Pam sediments and wave heights associated with changes in TC Pam’s track and intensity.

Key outcomes

We assessed the provenance of TC Pam sediments using two independent methods: (1) a statistical comparison of modern foraminifera with those from TC Pam sediments, and (2) a sediment transport calculation using measured storm surge flow depths and settling velocities from individual sediment grains. Each method corroborated the other and indicated that the storm surge associated with TC Pam scoured and transported material from the beach and nearshore environment (up to a depth of 5 m). These insights can be applied to older tropical cyclone sediments preserved in the geologic record and will help to determine how best to prepare for future storms. Our characterization of sediments deposited by a known tropical cyclone in Vanuatu can be used as an analogue for other storm studies that are conducted in tropical environments.

Products

Peer-reviewed papers

Kosciuch, T.J., Pilarczyk, J.E., Hong, I., Fritz, H.M., Horton, B.P., Rarai, A., Harrison, M.J., Jockley, F.R., in press. Foraminifera reveal a shallow nearshore origin for overwash sediments deposited by Tropcial Cyclone Pam in Vanuatu (South Pacific). Marine Geology.

Hong, I., Pilarczyk, J.E., Horton, B.P., Fritz, H.M., Kosciuch, T.J., Wallace, D.J., Dike, C., Rarai, A., Harrison, M.J., Jockley, F.R., in press. Sedimentological characteristics of the 2015 Tropical Cyclone Pam overwash sediments from Vanuatu, South Pacific. Marine Geology.

Conference presentations

Pilarczyk, J.E., Kosciuch, T.J., Hong, I., Fritz, H.M., Horton, B.P., Wallace, D.J., Dike, C., Rarai, A., Harrison, M.J., Jockley, F.R., 2017. Sedimentary record of Tropical Cyclone Pam from Vanuatu: implication for long-term event records in the tropical South Pacific. European Geosciences Union (EGU) General Assembly. 23-28 April 2017. Vienna, Austria. Abstract #: EGU2017-9579

Hong, I., Pilarczyk, J.E., Horton, B.P., Fritz, H.M., Kosciuch, T.J., Wallace, D.J., Dike, C., Rarai, A., Harrison, M.J., Jockley, F.R., 2016. Sedimentological characteristics of the 2015 Tropical Cyclone Pam overwash deposit from Vanuatu, South Pacific. American Geophysical Union (AGU) 2016 Fall Meeting. 12-16 December, 2016. San Francisco, CA. Abstract #: 143846.

Kosciuch, T.J., Pilarczyk J.E., Hong I., Fritz H.M., Horton, P.R., Horton B.P., Rarai, A., Harrison M.J., Jockley F.R., 2016. Assessing provenance of the 2015 Tropical Cyclone Pam sediments using foraminifera. IGCP 639. November 9-14. Muscat, Oman. Abstract #: N/A.

Fritz, H.M., Pilarczyk, J.E., Kosciuch, T.J., Hong, I., Rarai, A., Harrison, M.J., Jockley, F.R., Horton, B.P., 2015. Tropical Cyclone Pam field survey in Vanuatu. European Geophysical Union (EGU) General Assembly. April 17-22, 2016. Vienna, Austria. Abstract #: EGU2016-11105.

Kosciuch, T.J., Pilarczyk J.E., Fritz H.M., Hong I., Horton, P.R., Horton B.P., Rarai, A., Harrison M.J., Jockley F.R., 2016. Microfossil record of the Tropical Cyclone Pam deposit from Vanuatu: implications for documenting long-term records of South Pacific storms. Ocean Sciences 2016. November 9-14. New Orleans, LA, USA. Abstract #: 8871

Media

Supplementary Data

Microfossil data

Foraminiferal data (taxonomy and taphonomy) for surface sediment samples collected from Undine Bay, Efate Island.

Foraminiferal data (taxonomy and taphonomy) for TC Pam sediments and the underlying soils from Manuro (Efate Island) and PRB (Tanna Island).

Results of PAM cluster analysis for surface samples collected at Undine Bay using each scenario (taxonomic data, taphonomic data, and taphonomic/taxonomic data combined). Each of the three scenarios was clustered using all species documented within Undine Bay surface samples, followed by those present in at least 1% abundance in at least one sample. This was repeated at every 1% interval up to 15%. The scenario used for cluster analysis in Figs. 4, 5, and 6 is highlighted in grey.

Taxonomic list of species present at Undine Bay, Manuro, and PRB.

Settling Velocity data

Comparison of laboratory settling velocities with theoretical grain settling velocities

Grain size data

Comparison of laboratory settling velocities with theoretical grain settling velocities

Summary grain size statistics for Manuro trench (TC Pam sediments in bold).

Summary grain size statistics for trench PRB1 (TC Pam sediments in bold).

Summary grain size statistics for trench PRB2 (TC Pam sediments in bold).

Summary grain size statistics for trench PRB3 (TC Pam sediments in bold).

Summary grain size statistics for trench PRB4 (TC Pam sediments in bold).

Coastal Hazards Research Lab
Division of Marine Science
School of Ocean Science and Technology
University of Southern Mississippi
1020 Balch Blvd., Stennis Space Center, MS 39529