Abstract:
The great Indonesian earth quake (26
December 2004) triggered a tsunami wave across the
Bay of Bengal and Indian Ocean basins and has
brought a major havoc in several countries including
India. The coastal segment between Thotapalli and
Valiazhikal in Kerala state of southwest India, where
considerably rich beach placer deposit with ilmenite
percentage of more than 70% is concentrated, has
been investigated to understand the impact of tsunami
on coastal sediments. The grain size analysis
flashes out the significant differences between the
pre- and post-tsunami littoral environments. While
the mineral grains collected during pre-tsunami period
show well-sorted nature, the post-tsunami samples
represent moderately to poorly sorted nature.
Similarly, unimodal and bimodal distributions of the
sediments have been recorded for pre- and post-tsunami
sediments, respectively. Further, mineral assemblages
corresponding to before and after this major wave
activity clearly indicate the large-scale redistribution
of sediments. The post-tsunami sediments register
increasing trends of garnet, sillimanite and rutile. The
total heavy mineral percentage of the post-tsunami
sediment also shows an improved concentration,
perhaps due to the large-scale transport of lighter
fraction. Magnetite percentage of post-tsunami samples
reflects higher concentration compared to the pretsunami
samples, indicating the intensity of reworking
process. X-ray diffraction patterns of ilmenite grains
have confirmed the increased presence of pseduorutile,
and pseudobrookite in post-tsunami samples,
which could be due to the mixing of more altered
grains. SEM examination of grains also confirms the
significant alteration patterns on the ubiquitous mineral
of placer body, the ilmenite. The reason for
these textural, mineralogical and micromorphological
changes in heavy minerals particularly in ilmenite,
could be due to the churning action on the deeper
sediments of onshore region or on the sediments
entrapped in the near shelf region of the area, by the
~ 6 m high tsunami waves
