Methods
Our measured transect at the former resort originates at
the shoreline at 5◦26_32.5__N 95◦14_ 22.8__E. From there
it extends ∼400 m inland in the direction of flow, crossing
the inland limit of tsunami-deposited sand and continuing
another 40 m inland to the limit of tsunami inundation
(Fig. 2(a)). At 40-m intervals along this transect, we
measured sediment thickness, described the deposit stratigraphy,
and collected samples of sediment for later grain size
analysis.
Samples for grain size analysis were dry heated to 140◦C
for 48 hours before analysis. Few organics were present in
the sand; large organic debris (grass stems, twigs, etc.) was
removed with a forceps. The samples contained almost no
silt or clay, and were not rinsed prior to analysis.
We determined grain size within the deposit using a
Retsch Camsizer, an optically based instrument capable of
determining grain size to within ±1% over the range 30 μm
to 30,000 μm ( 5φ to −5φ). The instrument images a falling
curtain of sediment at 25 Hz, then determines the grain size
of each particle in the image, in our case by determining
the cross-sectional area of the particle and then reporting
the diameter of a circle of equivalent area. This tends to increase
the grain size relative to sieving, but probably yields
a result more compatible with settling tube. Because the
instrument made between 20 million and 40 million indiA.
MOORE et al.: DECEMBER 2004 TSUNAMI DEPOSITS IN ACEH, INDONESIA 255
Fig. 2. Views of the sediment transect about one month after the tsunami. White arrows show orientation and location of photos A-E. Black arrows show
flow direction inferred from oriented debris. Yellow bars identify the location of each sample location. A. Overview of the area looking northeast.
Sea to left. B. View seaward along transect, showing gaps through which water poured, and approximate flow depth from soil stripping on coastal
knolls. C. View landward along transect, showing maximum runup at back of valley. Pit in the foreground is the socket remaining where a tree had
been removed by tsunami. Stumps in middle ground (near standing people) are remains of trees that the tsunami snapped off near their base. D. Tree
roots exposed by tsunami erosion at seaward end of transect. Bark was abraded by debris and sediment in the water. Background shows that water
level decreased inland after flowing through the gap shown in B. E. Debris field near landward end of transect. Debris in the field records tsunami
inflow and outflow.
vidual measurements on our samples (depending on sample
size), the resulting dataset can easily support 1/16 φ to 1/32
φ resolutions.
Sample mean and standard deviation were determined
using the method of moments on 1/16 φ resolution data
from the Camsizer. Median grain size was determined by
linear interpolation of the 1/16 φ data.