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Tsunami hazard from volcanoes has been underestimated

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Tsunami hazard from volcanoes has been underestimated

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After Anak Krakatau erupted analysis of radar data have shown that the volume of material to create a tsunami hazard has been underestimated

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The scale of the tsunami hazard from volcanoes that collapse into the sea has been underestimated.

That's the conclusion of a new analysis of satellite pictures of Indonesia's Anak Krakatau showing the aftermath of its flank failure last December.

The study concludes that the volume of material that slipped into the water was actually relatively small.

And yet it generated destructive waves around the Sunda Strait as big as those expected from a much larger event.

More than 400 people died in the disaster on 22 December 2018; a further 7,000 were injured and nearly 47,000 were displaced from their homes.

Rebecca Williams from Hull University, UK, and colleagues have gone back and examined the satellite radar images that were taken of Anak Krakatau ("Child of Krakatau") before, during and after the volcanic activity that precipitated the flank failure.

Radar data was central to the analysis because this remote sensing technique can detect the ground surface even when it's dark, covered by cloud or, as in this case, obscured by erupted ash.

A key image in Dr Williams' study is one acquired by the EU's Sentinel-1a satellite which passed over the volcano just eight hours after its western flank had fallen into the water but before the 340m-high mountain's summit had been removed.

It helped her team to not only get a good calculation of the likely volume of lost material in the landslide but to also pick apart the different phases the event went through to produce an edifice that eventually stood little more than 100m above the surrounding ocean.

The estimated slip volume is 0.1 cubic km. This is a third of the volume that had been anticipated would produce the kind of tsunami witnessed on 22 December.

Scientists had modelled in 2012 what might happen if the western flank of Anak Krakatau gave way, and even worked out the likely height and arrival times of waves at nearby coastlines.

These projections turned out to be tragically accurate. However, they had presumed a tsunami-generating mass of 0.3 cu km.

"There's bound to be some error in the detail but we're confident that it was only a very small portion of the flank that collapsed to produce the tsunami," explained Dr Williams.

"The truly dramatic geomorphological (shape) changes we saw coming out a few days later in satellite images were due to the explosive eruption rather than the initial landslide event," she told BBC News.

How Anak Krakatau was remodelled

(1) The volcano had been in a periodic but persistent eruptive phase

(2) On 22 December its western flank failed, generating destructive waves

(3) This opened a vent to the sea. Huge explosions then removed the summit

(4) The volcano began to rebuild itself and closed off the underwater vent

These changes refer to the removal of the summit. The cone and crater are still visible and intact in the Sentinel image. They only disappear in subsequent days.

Dr Williams' team now think the flank collapse may have reorganised the plumbing of the volcano, opening a new vent that brought magma directly into contact with seawater. This would have initiated violent phreatomagmatic activity which is evident in the spectacular photos taken from an aeroplane that flew around Anak Krakatau in late December.

"The behaviour seen in those pictures was very typical of these marine explosions and it's this violence that removed the summit," she explained.

"Over the following weeks, as the volcano started to build again, the water was eventually stopped from getting into the magmatic system and Anak Krakatau went 'back to normal'.

"We went through the old literature and you see evidence of the vents migrating backwards and forwards, so this is something the volcanic island has done throughout its history."

Dr Williams concedes that many of the tsunami models out there currently cannot reproduce 22 December using a slip volume of only 0.1 cu km, although there is a new simulation from a French group that can, using 0.15 cu km.

"I would challenge that the models are currently underestimating the ability of these landslides to make these larger tsunamis," she said.

It's thought there are about 40 volcanoes worldwide sited close to water that could pose a hazard similar to that of Anak Krakatau.

Dr Williams' group has published its study in the journal Geology.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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Volcano's tsunami trigger was 'relatively small'

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The scale of the tsunami hazard from volcanoes that collapse into the sea has been underestimated. That's the conclusion of a new analysis of satellite pictures of Indonesia's Anak Krakatau showing the aftermath of its flank failure last December. The study concludes that the volume of material that slipped into the water was actually relatively small.

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Scientists have now found 26 previous unknown colonies of penguins through remote sensing 

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Scientists have now found 26 previous unknown colonies of penguins through remote sensing 

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Here is an article I located:

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It's one of the more bizarre, but amazingly forward-thinking conservation stories of our time.

The future of huge numbers of seabirds, including penguins, it turns out, may rely both on the colour of their poo, and how it looks from space.

If you're wondering how, then read on.

Seabirds, especially penguins can live in some of the remote and hostile places on Earth.

The sheer numbers living in Antarctica can be difficult to track, and so for the last few years scientists have been monitoring penguin colonies from space using satellite cameras.

If you've ever changed a baby's nappy you'll find their contents can be different colours, the same is true of penguins

When analysing the pictures they discovered something quite surprising. The colour of penguin poo - called guano - can be clearly spotted with satellite imagery.

What's more, researchers were then able to differentiate species of penguin by the changing colour of their guano stains against the white background.

Young penguin chicks have much darker guano than adult birds, so when factoring in the known breeding times of Adelie and chinstrap penguins, researchers showed in a recent study that they could identify their colonies from space based only on their unique guano "signatures".

These signatures were then built into an algorithm able to quickly differentiate the guano from the rest of the environment.

That this could be done was almost intuitive to Peter Fretwell of the British Antarctic Survey, one of the co-authors of the recent paper in PLoS One. "If you've ever changed a baby's nappy you'll find their contents can be different colours, the same is true of penguins," he explains.

Now in a new paper, a team also led by Fretwell, successfully managed to identify the breeding sites of all other seabird colonies with 50 pairs or more. They did this in a huge area on the west side of the Antarctic Peninsula, Marguerite Bay.

These seabirds, in addition to penguins, included Dominican gulls, skuas and southern giant petrels.

The unique signatures of their guano then allowed them to map where each colony was based and will now allow them to track where they move over time, findings they present in the journal Remote Sensing of Environment.

The density of their guano also gave good indications of the numbers of individuals in each colony of bird which had previously been difficult to obtain.

One emperor penguin colony has been completely lost. The prediction is we're going to lose a lot more over the coming 50 years

While using satellite data to monitor Antarctic seabird populations in this way is not new, it's yielding increasingly more insight into the lives of these animals over time. Once colony habitats have been established scientists then use higher resolution platforms or aerial photography to get more accurate population estimates.

Fretwell's team, for example, were the first to estimate the global population of emperor penguins from space. They discovered that there were twice as many colonies of emperor penguin in Antarctica than had previously been estimated.

It's great news for emperor penguins, says Fretwell, but they, like other species of penguin are at risk of losing their habitat as the climate continues to warm. Emperors are the only sea-bird which breed on sea ice, which is already shrinking in some parts of Antarctica. Estimates from climate scientists suggest it will continue to do so in the long term.

"In some places, for instance on the Antarctic Peninsula where we've seen losses of sea ice, one emperor penguin colony has been completely lost. The prediction is we're going to lose a lot more over the coming 50 years," says Fretwell.

Monitoring colonies over many years is therefore vital, he adds, to understand their population size, general breeding trends and the direct impact a changing climate will have.

Understanding these patterns will be a crucial starting point before scientists can begin to mitigate the knock-on effects of climate and over-fishing.

The team now hope to transfer their tracking skills to observe animals in other parts of Earth's most remote places.

Follow Melissa Hogenboom and BBC Earth on Twitter

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Watching penguins, and their poo, from space

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It's one of the more bizarre, but amazingly forward-thinking conservation stories of our time. The future of huge numbers of seabirds, including penguins, it turns out, may rely both on the colour of their poo, and how it looks from space. If you're wondering how, then read on.

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I'm Emily. I'm a second year environmental management student, looking forward to learning about how remote sensing is used, especially in boreal and arctic regions. Here is an article I located:  https://www.usgs.gov/centers/eros/science/monitoring-arctic-and-boreal-ecosystems-through-assimilation-field-based?qt-science_center_objects=0#qt-science_center_objects

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My name is Daniela I study Bsc Geography . I am looking forward to studying how to apply remote sensing.

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I'm Nati, I am a 3rd year exchange student from Israel studying Business and Geography. I'm looking forward to acquiring practical skills in this course, in addition to the more theoretical topics usually taught in academia.

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I'm Michal, I'm on a 2nd year of BSc Geography. I look forward to learn and practice remote sensing data collection and analysis and to apply it in any further projects I might participate in

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my name is Angelina, I am a 3rd year erasmus student from Germany doing Geography. I look forward to learn a lot of new things in this course that are different from the rest of my studied. Besides that, I am happy to learn useful skills and do practical work.

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I'm Amy, I study BSc Geography and I look forward to learning the application of remote sensing.

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My name is Scott, I am a 2nd year student studying environmental management. I am most looking forward to applying the skills I learn here to future research and/or my dissertation project. I am particularly interested in agriculture and how remote sensing can be implemented to make harvesting and crop growth more efficient. An article I found outlines how remote sensing from a UAV (unmanned aerial vehicle) can be used in precision agriculture to make the overall process more sustainable and limit environmental damage.  https://ohioline.osu.edu/factsheet/fabe-5541

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An accessible article outlining how remote sensing can be used in ecological studies

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Great article by @ScienceTaryn on remote sensing and new tools for ecologists and conservationists: Cameras in the sky https://t.co/jGYlCiFAhL

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Great article by @ScienceTaryn on remote sensing and new tools for ecologists and conservationists: Cameras in the sky https://t.co/jGYlCiFAhL

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Great article by @ScienceTaryn on remote sensing and new tools for ecologists and conservationists: Cameras in the sky https://t.co/jGYlCiFAhL
— Nick Murray (@remotelysense) June 12, 2018

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Great article by @ScienceTaryn on remote sensing and new tools for ecologists and conservationists: Cameras in the sky https://t.co/jGYlCiFAhL

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Great article by @ScienceTaryn on remote sensing and new tools for ecologists and conservationists: Cameras in the sky https://t.co/jGYlCiFAhL

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Great article by @ScienceTaryn on remote sensing and new tools for ecologists and conservationists: Cameras in the sky https://t.co/jGYlCiFAhL

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Maps and data produced vy DOPA for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on their web portal at http://dopa.jrc.ec.europa.eu/en/mapsanddatasets … Here you can download both printed maps and geospatial data. Have a look!

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All the maps and data we produced for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on our web portal at https://t.co/9pMD6tqJj3 Here you can download both printed maps and geospatial data. Have a look!

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All the maps and data we produced for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on our web portal at https://t.co/9pMD6tqJj3 Here you can download both printed maps and geospatial data. Have a look! https://t.co/q1qx7eopOO

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All the maps and data we produced for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on our web portal at https://t.co/9pMD6tqJj3 Here you can download both printed maps and geospatial data. Have a look! pic.twitter.com/q1qx7eopOO
— DOPA (@EU_DOPA) June 21, 2018

# data[].attributes.attachment_link.metadata.attachment_props_source.data.text
All the maps and data we produced for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on our web portal at https://t.co/9pMD6tqJj3 Here you can download both printed maps and geospatial data. Have a look! https://t.co/q1qx7eopOO

# data[].attributes.attachment_link.metadata.attachment_props.original_text
All the maps and data we produced for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on our web portal at https://t.co/9pMD6tqJj3 Here you can download both printed maps and geospatial data. Have a look! https://t.co/q1qx7eopOO

# data[].attributes.attachment_link.metadata.attachment_props.text
All the maps and data we produced for the #terrestrial, #marine & #pelagic #ecoregion coverage by #protectedareas are now available on our web portal at https://t.co/9pMD6tqJj3 Here you can download both printed maps and geospatial data. Have a look!

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The information collated on this page will hopefully provide you with lots of useful current and up to date ideas about how remote sensing data are being used to help monitor and manage the environment that we will live in.

An appreciation of how remote sensing is currently being used to address a range of issues will be very useful for you during this unit and is intended to supplement the journal articles currently on the reading list.

What should be posted to the Padlet

Each week I will ask each of you to contribute a "remote sensing" related item to the Padlet. This can either be a comment related to something you have read, a link to something interesting that you have observed on the internet, an interesting image that you have found or an interesting link to a Twitter tweet that you may have read. If possible always try to comment on any links posted i.e. tell us what it's about or why it is interesting.

Each week in class I will chose several posts from the Padlet and invite the authors of the posts to tell us a little about their post and why they found it interesting, so make sure that you actually "read" any links that you may chose to post to the class!

Happy posting!