Anak Krakatau: How a tsunami could wipe out the last Javan rhinos

[CaaC (John)+]

28 December 2018

Conservationists have warned that the entire species of the critically endangered Javan rhino could be wiped out if a tsunami were to strike again.

They once roamed the jungles of South East Asia and India, but today only 67 exist in the Ujung Kulon National Park, which was hit by last week's tsunami.

The park sits in the shadow of Anak Krakatau, the volcano which triggered waves that killed hundreds of people.

The volcano remains active and officials are now rushing to move them.

Two park officials were among the 430 killed by the tsunami, and numerous park buildings and ships were also destroyed when the tsunami hit last Saturday.

But the Javan rhinos left in the park - the only ones left in the world - were left unscathed.

The rhinos typically live along the park's south coast and this tsunami hit the north coast - many are keenly aware that the rhinos might not be so lucky if there is another disaster.

An entire species in danger

The Javan rhinos are the most threatened of the five rhino species in the world - and have been listed as Critically Endangered on the IUCN Red List.

They were once found in northeast India and across South East Asia but their population was quickly depleted as a result of poaching, habitat destruction through agriculture, among other factors.

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[nudge]

Nobody is safe in the Ring of Fire...Just hoping there won't be any volcanic activity similar to that in the 1800s. They should definitely try to establish a new population of those rhinos in a second site to ensure the survival of the species though.

[CaaC (John)+]

Anak Krakatau: Indonesian volcano's dramatic collapse

29 December 2018

The scale of the dramatic collapse of the Indonesian volcano that led to last Saturday's devastating tsunami in the Sunda Strait is becoming clear.

Researchers have examined satellite images of Anak Krakatau to calculate the amount of rock and ash that sheared off into the sea.

They say the volcano has lost more than two-thirds of its height and volume during the past week.

Much of this missing mass could have slid into the sea in one movement.

It would certainly explain the displacement of water and the generation of waves up to 5m high that then inundated the nearby coastlines of Java and Sumatra.

Indonesia's disaster agency says more than 400 people are confirmed dead with 20 or so still missing. In excess of 40,000 have been displaced.

The Centre of Volcanology and Geological Hazard Mitigation (PVMBG) has been studying pictures from a number of radar satellites, including the European Union's Sentinel-1 constellation and the German TerraSAR-X platform.

Radar has the advantage of being able to see the ground day or night and to be able to pierce the cloud.

The capability has allowed some initial measurements to be made of Anak Krakatau's lost stature, in particular on its western side.

What was once a volcanic cone standing some 340m high is now just 110m tall, says the PVMBG.

In terms of volume, 150-170 million cubic meters of material has gone, leaving only 40-70 million cubic meters still in place.

Quite how much mass was lost on 22 December itself and how much in the following days is unknown. Scientists may have a better idea once they have had a chance to visit the volcano and conduct more extensive surveys.

But with the eruptions still ongoing and a safety exclusion zone in force - no-one is going near Anak Krakatau.

Cone collapse with tsunami generation was considered a potential hazard before last Saturday.

Scientists had modelled the possibility six years ago, even identifying the western flank of Anak Krakatau as the section of the volcano most likely to fail.

The study, although simulating a larger event, predicted wave heights and coast

https://www.bbc.co.uk/news/science-environment-46707731

[CaaC (John)+]

Anak Krakatau volcano collapse: 'Warning signs were there'

Anak Krakatau, the Indonesian island volcano that collapsed last December triggering a huge tsunami, did produce clear warning signals before the event.

That's the assessment of a German-led team which has reviewed all the data.

The scientists say satellites in the months leading up to the catastrophe had observed increased temperatures and ground movement on the volcano.

Earthquake and infrasound activity was also detected two minutes prior to the collapse of Anak's southwestern flank.

When this mass slid into the sea, it sent a wall of water, up to 4m high, around the Sunda Strait.

More than 400 people died in 22 December tragedy; a further 7,000 were injured and nearly 47,000 were displaced from their homes.

Thomas Walter, from the German Research Centre for Geosciences GFZ in Potsdam, said any of the different signals viewed individually could not have been used to predict what happened at the island volcano, but taken together they might well have raised a red flag.

"If you took any of the sensors on their own, the interpretation would not be robust, but by pulling together all of the different sensors we can draw a picture of the cascade that was going on," Dr Walter told BBC News.

The team noted that the volcano was experiencing its greatest eruptive phase in 20 years in 2018; that its southwestern flank had begun edging seaward from January onwards; that there was an intense phase of thermal activity initiated on the 340m-high mountain in June, and that there had been an increase in the island's surface area in the months leading up to the collapse.

There was also significant seismic behaviour just before the collapse. Perhaps an earthquake, maybe an explosion; it's not clear.

But what was interesting, explained Dr Walter, was that this seismic signal did not go down to zero. And when it picked again, it displayed a low frequency that is characteristic of landslide behaviour.

A couple of minutes further on in time, the frequency changes again, which the team interprets as a barrage of volcanic explosions - as "the cork comes off the top of the bottle".

As to how the lessons learned at should be used at other vulnerable volcanoes, Dr Walter said the kind of flank movement observed Anak Krakatau could be regarded as a potential long-term precursor.

Radar satellites will detect this deformation and a number of groups around the world are even developing automated systems where algorithms hunt through the spacecraft data for evidence of anomalous activity.

Last December, seismic and infrasound networks caught the moment of collapse. "But we have many volcanoes around the world where there are no such stations nearby," Dr Walter said. "We should look at those volcanoes where there is a risk of sector collapse and invest in a densification of instruments."

The GFZ volcanologist's team has published its findings in the journal Nature Communications.

https://www.bbc.co.uk/news/science-environment-49907007