Why Indonesia Issued and Lifted a Tsunami Warning After the Flores Earthquake
A powerful earthquake near Indonesia’s Flores region prompted a tsunami warning because large, shallow earthquakes near coastlines can suddenly move the seafloor and displace seawater. The event caused deaths and building damage, according to the Associated Press, while Indonesia’s warning system later ended the tsunami alert after monitoring found no significant sea-level change threatening coastal communities.
Why an earthquake can create a tsunami
Earthquakes generate tsunamis when they cause a substantial, rapid movement of the seafloor. The greatest risk usually comes from shallow earthquakes involving vertical motion, such as thrust or reverse faulting. That movement lifts or lowers the water column above the rupture zone, sending long waves outward across the ocean.
Magnitude alone does not determine whether a tsunami will occur. A very large earthquake may produce little tsunami movement if it happens deep underground, mostly shifts the ground sideways, or occurs beneath land. Conversely, a smaller but shallow seabed rupture can sometimes produce dangerous waves.
The Flores region is especially sensitive to earthquake hazards because it lies within the complex boundary zone where the Australia and Sunda plates converge. The U.S. Geological Survey describes the area as containing active thrust systems, including the Flores Back Arc Thrust, capable of producing damaging earthquakes.
How the warning process works
Indonesia’s InaTEWS combines earthquake-location data, magnitude estimates, depth calculations, coastal sensors, tide gauges, and numerical tsunami models. The first alert is deliberately cautious because officials must act before they know exactly how much water has moved.
A typical sequence is:
- Seismic detection: Sensors estimate the earthquake’s location, depth, and magnitude.
- Threat assessment: Authorities evaluate whether the fault movement could displace the seabed.
- Public warning: At-risk coastal communities may be told to move inland or to higher ground.
- Sea-level confirmation: Tide gauges and other instruments check whether a tsunami has actually arrived.
- Update or cancellation: Officials maintain, revise, or end the warning as evidence improves.
This means a warning is not proof that a tsunami has already struck. It is an emergency precaution based on the earthquake’s early characteristics and the potential consequences of waiting.
Why the alert may be lifted
If instruments do not record threatening sea-level changes and updated modeling lowers the estimated risk, authorities can cancel the warning. That decision does not mean the earthquake was harmless: strong shaking, landslides, damaged buildings, fires, and aftershocks can remain serious dangers.
The history of Flores also explains the caution. A major earthquake in the region in 1992 generated a deadly tsunami, making rapid evacuation guidance particularly important. The safest response during a strong coastal earthquake is to move away from the shore immediately and follow official instructions rather than wait for a second message.