New Insights Are Provided By Ritter Island Into The Volcanic Landslide’s Dynamics

The reason of the tsunami was quickly disclosed: most of the volcanic island of Ritter Island, 150 kilometers from Finschhafen, had slid into the sea in a single catastrophic collapse. However, some questions about the exact course of the landslide are still unanswered.

A study is published in the global magazine Earth and Planetary Science Letters. Researchers from the GEOMAR Helmholtz Center for Kiel Ocean Research, along with colleagues from the University of Birmingham, the University of Malta, the University of London and the German Center for Geoscience Research, have published it showing the volcanic slope of Ritter Island had already slipped before the catastrophe of March 13th, 1888, but much more slowly. Dr. Jens Karstens of GEOMAR, first author of the study, said that these new findings help us better assess the danger potential of other volcanic islands.

The study is on the basis of SO252 expedition of the German research vessel SONNE to Ritter Island in the fall of 2016. With seismic methodologies, the global team led by Prof. Dr. Christian Berndt (GEOMAR) measured the traces of the 1888 disaster Evidence accurately. It was found that the flank of the island had moved sporadically for a longer period of time before 1888. This is showcased by the corresponding deformation of the subsoil in a smaller volcanic cone off the coast of Ritter Island.

It is not known whether the slow landslides on the volcanic flanks precursors of a catastrophic collapse are, or even if they could lower the risk of these kind of collapses as they relieve the tension of the volcanic system. Dr. Karstens said that on Ritter Island, they now have proof that sporadic detachments have preceded a much larger one.

Both kinds of landslides were analyzed last year in active volcanoes. Last year's eruption of Kilauea in Hawaii was accompanied by a landslide from the flank of the volcano causing a moderate earthquake. The eastern flank of Mount Etna in Sicily is also slowly shifting towards the sea, as represented in a study published in the autumn of 2018. An eruption of the Anak Krakatau volcano caused a landslide in December 2018 which triggered a tsunami in the Sunda Strait (Indonesia) and killed more than 400 people. The events at Anak Krakatau can be compared to those which took place on 13^th March, 1888 at the Ritter Island volcano. This reflects the relevance of the findings on Ritter Island for hazard assessments on volcanic islands around the world.

According to Dr. Karstens , the better they know the dynamics of these type of events, the better they can assess the danger for a given region. Ritter Island is a superb case study as the volcano shows many other volcanic islands and as the eruption and tsunami are well documented.

By: Preeti Narula

Content: https://www.sciencedaily.com/releases/2019/05/190516114625.htm