A Tsunami swept across Indonesia's islands of Sumatra and Java the night of December 22, 2018 just before 9:30 p.m. local time. What was different about this Tsunami you ask? This one was triggered by the collapse of a portion of the Anak Krakatau volcano during an eruption which caused the killer waves. See image (Source: Indonesia’s Disaster Management Agency through Twitter). There was no warning for this event which amplified the devastation on these islands.
The maximum reported impact was a wave of more than 16 feet at the village of Sumur on the coast of Java. 429 died and over a thousand injured. The waves destroyed hundreds of buildings, sweeping away cars and uprooting trees in several popular tourist destinations.
Source of the event: Anak Krakatau volcano is the product of the infamous Krakatoa volcano, which roared to life in 1883 in one of the largest eruptions of modern times. Massive Tsunamis with waves of up to 41 meters hit the coasts of Java and Sumatra and also travelled several thousand miles away and killed more than 35,000 people. In 1927, Anak Krakatau, or "Child of Krakatoa", emerged from the caldera formed in 1883.
Anak Krakatau has been erupting since June 2018 and the December 22 eruption was not the biggest. The October-November 2018 period had larger eruptions, however, December 22 saw the most devastation because of the landslide.
A Tsunami can be triggered by four processes: earthquakes, landslides, weather causes (storms), and volcanic eruptions. Most of the destructive Tsunamis are triggered by earthquakes and the Tsunamis triggered by landslides usually have shorter periods and higher run-ups than those driven by tectonics as in the Anak-Krakatau case. Landslide triggered Tsunamis have happened in the past. The 1883 Krakatoa, Indonesia (landslide due to volcanic eruption), with 42m wave; 1958 Lituya Bay, Alaska, US (landslide caused by an earthquake) with 520m wave; 1963 Vajont Dam, Italy (man-made) with 250m wave; the famous 1980 Spirit Lake, Washington, US (collapse of Mount St. Helens and subsequent volcanic eruption) with 260m wave are some notable ones.
Indonesia also saw a "surprise Tsunami" that battered Palu last September; which was caused by a M7.5 earthquake at occurred north of Palu city. This Tsunami was also a complex geological phenomenon which took the scientific community by surprise. Here, in addition to the complexity of the geological phenomenon, the narrow bay area also amplified the Tsunami wave height killing 1400 and causing massive destruction.
Concluding Thoughts: There was knowledge of a potential Tsunami in the scientific community (2012 paper by by T. Giachetti, R. Paris, K. Kelfoun and B. Ontowirjo), there was knowledge of the volcano being active and erupting. But, even in the midst of this predictability we were not able to effectively mitigate the devastation caused by this Tsunami. Unpredictable events still ensue; the geological events are complex, novel and irregular, are we prepared?
Category: Climate/natural disasters: Disaster risk