Indonesia tsunami claimed 1,350 lives: Why wasn't there an early warning?

The location of the tsunami may have made the destruction particularly acute, but the country's early warning system also appears not to have lived up to expectations.

Business Standard : The recent earthquake and tsunami in Indonesia has claimed the lives of at least 1,350 people. Many more people are missing and the disaster has destroyed homes and businesses across the city of Palu and surrounding area on the island of Sulawesi.

Yet after the much larger tsunami that devastated countries around the Indian Ocean in 2004, Indonesia began installing a new early warning system to try to prevent such widespread destruction from happening again. So why is the country once again facing such a severe loss of life? The location of the tsunami may have made the destruction particularly acute, but the country’s early warning system also appears not to have lived up to expectations.

A tsunami (Japanese for “harbour wave”) is formed when a disturbance on the sea floor leads to a series of large waves which spread out across the ocean. This disturbance can be caused by a large earthquake, an underwater landslide, or even a volcanic eruption.

When the tsunami waves reach shallow water as they move towards the shore, the speed of the wave slows down and causes the water to dramatically pile up. The increase in wave height leads to devastating coastal flooding especially in highly populated, low-lying areas.

The height of the wave depends on the size of the tsunami wave but also by the shape of the coastline. For example, tsunamis will have a greater impact where the wave moves through a narrow, elongated bay, like Palu, as it approaches the shore. The earthquake in Sulawesi likely disturbed sediments on the seabed and triggered a local underwater landslide. These two factors combined could explain the six-metre waves that reached Palu.

More than one wave can occur during a tsunami, meaning that such events can continue to impact the coastline over a number of hours. It can be the case that the second, third or even later waves can be the biggest.

Early warning systems

Unfortunately it isn’t possible to predict exactly when a tsunami may strike a coastal area, but there are clues that can save lives. Indonesia’s main early warning system is made up of a network of tidal gauges that measure sea level, and land-based stations that detect earthquake activity. However, the tidal gauges were so far away from Palu that they only registered a small rise in the water level as the waves started to form.

It’s possible the system wasn’t set up to take into account how the waves would grow as they travelled down Palu’s bay.... Read More