Sempu Island

Sempu Island, East Java

Tsunami damage occurred along a sheltered channel separating Sempu (pronounced sem-poo) Island from mainland Java. Sempu, an irregularly-shaped island four km across at its widest point, lies approximately 50 km south of the Malang. The channel, roughly 0.5 km wide, runs from southwest to northeast between Sempu and the mainland. Sendangbru, a small fishing village, is located on the mainland at the southwestern end of the channel; it lies in the shadow-zone of Sempu Island and hence is protected from the typical swell of the Indian Ocean. The fishing village was not, however, protected from the tsunami attack. A run-up height of 3.6 m was measured, based on an eyewitness' estimation of the tsunami height along a fish cannery wall. Further up the channel, still on the mainland, a run-up height of 3.4 m was measured. Eyewitnesses reported a total of three waves, with the third wave the largest.

Perhaps the most interesting evidence of the tsunami attack was observed on Sempu Island itself. The island is a nature preserve and is uninhabited, hence no loss of life or damage to dwellings were reported on Sempu. The survey team did observe significant shoreline erosion in a small cove lying to the northeast of the fishing village. A long, narrow depression was formed, cutting inland through a forested valley bordering the beach. Sandy topsoil had been removed to create the one-m-deep depression, which was roughly funnel-shaped, 15 m wide at the shoreline and extending 50 m inland. The extensive erosion and onshore sediment transport observed in the cove lead us to conjecture that this area may have been subject to wave splash-up; this phenomenon occurs at the point where two trapped wave fronts propagating around an island's perimeter meet. This speculation is corroborated by eyewitness accounts in the fishing village at the channel's southwestern end: the natives reported a first wave approaching from the southwest, and then a second wave following from the northeast. The two waves would have therefore met somewhere to the northeast of the fishing village, which is where the small cove lies.

This account has been adapted from Synolakis et al.

Runup Data

1994 Survey Images