Transcript PowerPoint Presentation - UNT Geography

Geologic records of Holocene typhoon strikes
in the Gulf of Thailand; a preliminary link
between extreme storms and climate change?
Harry Williams - University of North Texas
Montri Choowong - Chulalongkorn University, Thailand.
Sumet Phantuwongraj - Chulalongkorn University, Thailand.
Peerasit Surakietchai - Chulalongkorn University, Thailand.
Thanakrit Thongkhao - Chulalongkorn University, Thailand.
Stapana Kongsen - Chulalongkorn University, Thailand.
Eric Simon - University of North Texas
BACKGROUND
Typhoon strikes on the Gulf of
Thailand coast are rare, but
devastating.
Typhoon Gay (1989)
• Category 3 typhoon at
landfall
• over 800 fatalities in
Thailand
• 11-m-high swells
• US$497 million in losses
How frequent are typhoons?
• Don’t know – there’s no
long-term record.
• Thai Meteorological records
start in 1951.
Is typhoon variability tied to
climate change?
• A millennial-scale record of
typhoon strikes is required
to explore linkages to
climatic changes.
Tropical Cyclone Storm Surge
PALEOTEMPESTOLOGY - OBJECTIVE
• Find prehistoric typhoon-deposited sand layers in lowenergy sedimentary environments.
• Sand layers are offshore/beach/dune sands that have
been transported inland – “anomalous”
• Primary diagnostic for recognizing washover sand layers
are sharp contacts between coarser sand layers and finer
in-situ sediments.
STUDY AREAS
Cha’am
coastal
marsh
(site HW1)
Kui Buri swales (site SRY)
CORING SITES
METHODS
RESULTS – EXAMPLES OF SAND LAYERS
Examples of suspected storm-surge-deposited sand beds. a. Coarse
sand bed (CS), with gravel-sized clasts at site V5, Cha’am.
b. Multiple mud rip-up clasts (MRC) in a sand bed at site SRY 3,
Kui Buri. Both sand layers are enclosed by, and have sharp contacts
with, fine-grained marsh or swale deposits.
STRATIGRAPHY – CHA’AM
KUI BURI
DATING THE SAND LAYERS
At each site, radiocarbon dates were used to
construct age-depth models , which were used to
estimate the age of each sand layer.
Estimated ages of typhoon strikes at Cha’am and Kui Buri.
Horizontal line through data points represents period of
record at each site. Yellow boxes represent potentially
coeval typhoon strikes recorded at both sites.
• Fifteen typhoon strikes (including coeval strikes) in
8800 years.
• Typhoon strikes over three times as frequent in
3500-7000 cal. yr BP than in 0-3500 cal. yr BP.
WHAT COULD HAVE CAUSED TYPHOONS TO BE MORE
FREQUENT IN THE MID-HOLOCENE?
Increased Northern Hemisphere solar forcing in the midHolocene resulted in the Mid Holocene Warm Period. In
the North Pacific, ENSO activity was reduced during this
period. There is evidence that suppressed ENSO activity
causes an westward shift in tropical cyclone genesis
location. As a result, tropical cyclones are more likely to
follow more southerly storm trajectories, striking South
East Asia (including Thailand); under enhanced ENSO
conditions, an eastward shift in tropical cyclone genesis
location results in more northward recurving trajectories,
leading to greater likelihood of tropical cyclone strikes on
Japan and Korea.
Study results from Thailand appear to support this model of
an oscillating pattern in tropical cyclone activity between
the northern and southern western North Pacific.
PRELIMINARY CONCLUSIONS/QUESTIONS
1. Sand layers most likely record typhoon strikes. Evidence: rarity,
sharp contacts, gravel-sized clasts, mud rip-up clasts, plant
fragments, offshore foraminifera (in some layers).
2. Preliminary evidence of more frequent typhoons in the midHolocene (3500-7000 cal. yr BP). Could this be a result of an ENSOdriven oscillating pattern of typhoon activity between the
southern and northern western North Pacific?
3. Could another climatic “warm period” (ongoing global warming)
cause an increase in typhoon strikes in Thailand?
4. More work is required to improve age control and confirm a
mid-Holocene tropical cyclone hyper-active period in SE Asia.
Acknowledgments: This material is based upon work supported by the National Science
Foundation under Grant No 1305787. Thailand Research Fund (TRF:BRG5780008) and
Chulalongkorn University (CU57-058-CC), a UNT Charn Uswachoke International
Development Fund award and a grant from the UNT Small Grants Program.