Tsunami Survey
The highest runup measured (~5 m) was on
the south side of Victoria Bay on Kairiru Island. High runup
values were concentrated on the west-facing bays of Kairiru and
Mushu Island and on the mainland to the south and west. Runup
and inundation tapered off gradually to the east and west of
these centralized maxima. Due to the possible amplification of
runup heights in the western facing bays of the offshore islands
(Kairiru and Mushu) the field data in Figure 4 have been divided
into mainland data points and island data points.
Western Region
To the west of Aitape, there
was very little tsunami activity. Residents in the area reported
feeling the earthquake very strongly but generally did not notice
any extreme water motions. At Sissano Lagoon, a site which was
completely devastated in the 1998 tsunami, one fisherman reported
strong surges flowing through the mouth of the lagoon. These
surges persisted for some hours after the earthquake. To the
east at Malol, the residents reported that, having fled the coast
after the earthquake, upon returning they noted a uniform line
of small coral pebbles deposited along the beach. This line was
later washed away by high tide, however some were still present
at the time of the survey 2 weeks after the event.
Photos from Sissano (top row) and Aitape.
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At Aitape, the tsunami was noticed as a
series of surges that flowed up the Aitape River and spilled
over the banks and flooded some residents' gardens. Many distinct
surges were reported at Aitape, with the first and largest coming
30 minutes after the earthquake. Residents estimate that there
were as many as 12 surges continuing for up to 2 hours after
the earthquake. The earlier surges were the largest and caused
the inundation over the riverbanks. The Eastern Shore of Seleo
Island offshore of Aitape was also visited. Residents reported
unusually low water levels for up to 1.5 hours after the earthquake
followed by a maximum positive surge of 1.2 m. Further east on
the mainland, residents in the village of Paup reported that
their canoes were moved by a surge some 30 minutes after the
earthquake. They reported up to two surges reaching over 2 m
above sealevel. This is in contrast to the next site eastward
on the mainland, Suain, where the residents reported no positive
surge, however they did note that the ambient tide level seemed
'lower than normal' for several days after the earthquake.
Central Mainland Region
The central region from Kauk
to Cape Moem, including the offshore islands, was the area most
affected by the tsunami. On the mainland, the village of Kauk
experienced a positive surge of nearly 1.8 m while 15 km to the
east at But, there was no wave activity at all. The villages
of Karawop, Boiken, Krupier and Yuo were all affected by the
tsunami. Of the three, Boiken, situated on the eastern side of
a small headland was the hardest hit. Three distinct surges were
reported. The first came in uniformly from the sea while the
second came from the west, sweeping across the exposed portion
of the headland and along the shoreline through the village.
Two individuals were entrained by the flow and nearly drowned.
Maximum runup was measured at over 2 m while inundation distances
varied between 75 and 190 m.
At Krupier, east of Boiken in the bay formed
by the Boiken headland, the surge came in directly from the north,
overtopped the beach berm flowed through the village and into
the swamp behind it. Flow depths in the village were estimated
between 40 to 60 cm, lower than the floors of the local stilted
huts, i.e., the material inside the huts was not wetted
by the wave. Inundation of 80 m was measured to the edge of the
swamp, however this is a minimum value since the surge continued
inland through the dense swamp.
Maps and photos from Boiken.
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Slightly smaller runup was measured to
the west at Karawop and to the east at Yuo Village at the mouth
of the Hawain River. It should be noted that Yuo Village is situated
10 km east of Boiken on a headland very similar in size and shape
to the Boiken headland, however the tsunami was much smaller
and less energetic than at Boiken.
Keresau, Walis and Tarawai
Offshore of this area are the
islands of Keresau, Walis and Tarawai (Figure 2). Keresau, which
lies closer to the mainland, directly offshore of the Boiken
headland, experienced some flooding and positive runup. Three
locations were measured on the southern shore of Keresau facing
the mainland. Here residents observed the wave flooding the village
grounds. A clear debris line was also observed. Runup was measured
between 0.9 and 1.1 m with inundation distances of 10 to 30 m.
Along the north shore of Keresau, there were no eyewitnesses
and there was no reliable indication of a positive wave.
Photos from Walis and Tarawai.
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Further offshore on Walis and Tarawai islands,
residents only reported a withdrawal of the sea with no positive
wave: shortly after the earthquake the sea withdrew and stayed
out for many hours. The reefs were exposed some 500 m offshore.
The islands of Tarawai and Walis have been clearly uplifted.
Rough estimates of uplift on Tarawai were taken by comparing
the current high tide (measurements happened to be taken at high
tide) to the levels of other high tide marks. Our measurements
yielded an uplift of 50 cm on the eastern end of Tarawai Island.
Evidence of uplift was also observed on Walis Island. On this
particular day at high tide, the sea level was observed to be
30 to 50 cm less than the level normally expected for the high
tide, as indicated to the ITST by local residents on a log bridge
and on the root outcrop of a tree growing at the shoreline.
Mushu and Kairiru Islands
The two large islands of Kairiru
and Mushu which lie to the northwest of Wewak were greatly affected
by the earthquake and tsunami. Kairiru is a rugged steep island
with a maximum elevation of 760 m while Mushu is much flatter
with elevations only reaching 120 m. Both islands have west-facing
bays that seemed to have trapped the incoming tsunami wave and
amplified the runup. The largest runup was measured on the south
side of Victoria Bay on Kairiru Island. A clear water mark and
debris line was measured at 5.5 m. Also in Victoria Bay the village
of Shauer on the north side of the bay was inundated by the wave.
The wave penetrated over 100 m and reached an elevation of 2.1
m. At the head of Victoria Bay, there was evidence of overtopping
of the berm and of inundation up the small river.
Photos from Kairiru.
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On Mushu, the village of Warak was inundated
to a distance of 100 m and a maximum runup of 1.5 m. Two structures
were damaged by the tsunami in Warak and there was extensive
evidence of tsunami sand deposition. A uniform layer of white
beach sand approximately 1 2 cm thick was overlain atop
a layer of thick black mud. There was also evidence of the flow
depth at Warak given by watermarks on the Sago Palm trees at
the back of the village some 70 m inland.
Tsunami deposits at Warak on Mushu Island
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East to Wewak
Along the mainland east to
Wewak, a village on the Wom Peninsula was inundated. The inundation
was 40 m with a runup of 0.66 m. Just to the west of Wom, at
Cape Pus and the entrance to the Pus Lagoon, one resident, who
had gone there to fish several hours after the earthquake, reported
seeing surges flowing in and out of the lagoon. He also noted
that water was flowing out of cracks in the ground near shore.
In Wewak, three locations were surveyed.
Along the main beach at a petroleum depot, a night watchman reported
that a surge flowed over the seawall and on to the coastal road.
There were also reports of unusual surges flowing up a drainage
canal, for up to few hours after the earthquake, as also observed
at Aitape and Cape Pus. East of Wewak at Moem, there were also
reports of a tsunami after the earthquake. Several locations
were surveyed and runup was measured at approximately 1.2 m.
There was evidence of sand deposition from the tsunami overtopping
a sea wall and flooding across a coastal road. No data was taken
between Moem and the Murik Lakes area due to accessibility and
time constraints.
Murik Lakes
In the far eastern region of the survey area, the Murik Lakes
area features a series of lagoons and barrier islands with very
low topographic relief. Local residents say that their land is
regularly flooded by strong ocean swells. Three locations were
surveyed which all gave similar accounts of the sea rising above
the berm (~ 1 m) while the lagoon level also rose, flooding the
villages from inland, to a depth of 30 cm to 1 m.
Pictures from Murik Lakes. the
narrow sand spit was over topped with flooding coming from both
the sea and the lagoon.
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