Comets and Asteroids - Tsunami - page 177

(a)

(b)

Taolagnaro

Itampolo
Bay

Karagan
Lagoon

Ampalaza

Fenambosy Faux Cap

Madagascar

North West
Cape

(c)

Burckle Impact Site

Fig. 9.10 Location map of the Indian Ocean with reference to 2807
BC Burckle impact event. a Location of Burckle impact crater and sites
around the Indian Ocean showing tsunami evidence linked to this event.

b Location of major chevrons in Southern Madagascar. c Google Earth
image of the Ampalaza chevron, Southern Madagascar. Both the apex at
the northwestern end and southern flank exhibit recent aeolian activity

of well-defined, smaller, internal chevrons. It is tempting to
ascribe the chevrons to prevailing winds; however, careful
measurement of their orientation reveals that they are
aligned with modeled wave refraction patterns coming from
a point source located in the vicinity of the Burckle crater. In
addition, the sediments in the chevrons are unsorted with a
broad range of particle sizes ranging from small boulders
down to clay particles. The chevrons also contain micro-
fossils—with surface splash particles of molten native
metals—indicative of a marine source from the Madagascar
outer shelf. Finally, dump deposits, containing rock frag-
ments typical of mega tsunami processes, were found east-
ward from the Fenambosy chevron to Cap St. Marie. Many
of the rock fragments were not locally derived. The age of
the Madagascar chevrons is presently unknown. However,
there are tsunami deposits in the Indian Ocean region similar
in age to that of 2807 BC determined from legends. Besides
the orientation of chevrons on the West Australian coast, two
samples of coral lying in boulder ridges up to 7 m above sea
level on the North West Cape date around this time
(Scheffers et al. 2008b ). There is also a tsunami deposit at
Karagan

centered around 2984 BC ( Fig. 6.13 ) (Jackson 2008 ). Given
the error bars on this date, the latter deposit could be a
product of the Burckle event.

9.5.4 The Mahuika Comet Event and Eastern

Australia

Paleo-tsunami larger than the historical events described in
Chap. 1 are possible. The evidence from Eastern Australia
for cosmogenic mega-tsunami is based upon the magnitude
of geomorphic features and their contemporaneous occur-
rence over a wide region of the Tasman Sea (Fig. 9.11 b).
This chronology coincides with the timing of legends and the
sightings of comets and asteroids over the last millennium
(Rasmussen 1991 ; Hasegawa 1992 ; Steel 1995 ). Figure 9.
11 c shows the location of a possible comet impact lying in
300 m depth of water on the continental shelf 250 km south
of New Zealand at 48.3S, 166.4E (Abbott et al. 2003 ). The
crater is 20 km in diameter and could have been produced by
a comet 1.6 km in size traveling at a speed of 51 km s -1 (all
calculations based on Marcus et al. 2005 ). When it struck, it Lagoon, Sri Lanka having a radiocarbon age