[Coral-List] Tsunami effects on coral reefs - previous examples

David Evans devans at geo-marine.com
Wed Jan 12 19:57:03 EST 2005

Those interested in looking at the long-term (100+ years) recovery of reefs
might consider looking for signs of the Krakatoa explosions/tsunamis event
that occurred in 1883. It is likely that this has already been considered by
many. Direct signs of tsunami effects on reefs in the Indian Ocean may be
difficult to locate or verify, however several passages in Stoddart (1971)*
seem to point to the effects of tsunami waves at Deigo Garcia in the Chagos
Archipelago. One interesting passage references a survey conducted by G.C.
Bourne in 1885. [page 12, section 3. Narrow rim]: "Because of the narrowness
of the rim in this sector [northeast land rim], breaches and washovers from
sea to lagoon are not uncommon: Bourne found recent cuts in 1883[sic]" (the
text reads "1883" however Bourne completed his survey in 1885 and published
in 1888). The recent cuts that Bourne noted are likely effects of the
tsunami generated by the Krakatoa event hitting the eastern side of the
island. Another passage [on page 13, section 4. Rim ends], Stoddart states:
"At Barto Point, at the entrance to the lagoon [northeast side of the
island] the reef flat is covered with boulders 0.5-1 m in diameter for a
distance of several hundred meters (plates 3-4). This is unusual on Deigo
Garcia reef flats, and may have resulted from the effects of a single major
storm." The problem with attributing the boulders to a major storm is that
the Chagos do not experience major storms. They are too close to the equator
for Typhoons to form. The most they experience is possibly tropical
depressions. No major storm of Typhoon class has been recorded at the Chagos
in history. Also, the size of the boulders possibly indicates that rather
than a single storm surge that would be generated by a storm, the atoll
experienced a series of waves that first broke corals loose, knocked them
around, and then washed up the boulder sized pieces on the reef flats and
shores. The Krakatoa event generated a series of waves rather than just one
surge, which is more likely to lift larger pieces of reef and deposit them
on shore. It might be interesting to consider the Krakatoa event when
considering long term reef recovery and baseline conditions in the Indian
Ocean. I would also like to wish godspeed to all recovery and aid efforts in
the region.

*Stoddart, D.R. 1971. Geomorphology of Deigo Garcia Atoll. in: D.R. Stoddart
and J.D. Taylor eds. Geography and Ecology of Diego Garcia Atoll, Chagos
Archipelago. Atoll Research Bulletin No. 149. Issued by the Smithsonian
Institution, Wahsington D.C.


David Evans

David J. Evans
Marine Biologist
Geo-Marine, Inc.
550 E. 15th St.
Plano, Texas, USA
Phone: 972-423-5480
Fax: 972-422-2736
e-mail: devans at geo-marine.com

Message: 2

Date: Tue, 11 Jan 2005 23:20:44 -0800

From: Dida <didak at jps.net>

Subject: [Coral-List] fish bombing and tsunami  effects

To: coral-list at coral.aoml.noaa.gov

Message-ID: < at mail.jps.net>

Content-Type: text/plain; charset="us-ascii"; format=flowed

About 6 years ago when I was actively research diving in Palau Sipidan

(MY), and disturbed by the number of coral reef sites decimated by illegal

fish bombing, I asked around (many contacts made via this list) about the

rates of coral growth after such destruction. I head reports that healthy

coral reefs are in place after only 10 years. Considering the effects of

the tsunami, is a comparable rate of regrowth considered reasonable?

Also, does anyone on this list have current contact info for Arnaz Mehta?

Last I heard, she was a research diver in Sumatra (she was the person who

found the coelacanth in an Indonesian market place, thus leading to proof

of a wider distribution of the mysterious "dinosaur fish").

Dida Kutz

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