On 17 October 2015, a huge landslide occurred at the bottom of Tyndall Glacier, within the Wrangell-St Elias National Park & Preserve, Alaska. The resulting loosed material – 180 million tons of rock – fell into the relatively recently deglaciated Taan Fjord, only exposed over the past half-century as the glacier has gradually retreated (as much as 400m between 1961 and 1991). The impact caused a huge swell that travelled south down the fjord, flattening surrounding alder forests with waves that reached as high as 193 metres, taller than St. Paul’s Cathedral (by comparison, the largest recorded wave created by the 2004 Indian Ocean tsunami reached a peak of 51 metres, in Labuhan, Indonesia).

Tsunamis are likely to be forever associated with destruction along ocean coastlines, as the literal Japanese translation ‘harbour wave’ makes clear. But climate change is introducing new, more powerful tsunamis far from the sea, as glacial retreat creates large bodies of water that are exposed to crumbling mountain landscapes. The resulting landslides and tsunamis are being unleashed on unsuspecting remote communities. Similar scenarios to the events in Taan Fjord have been reported in glacial regions such as Norway and Patagonia, and even cost the lives of four Greenlanders when they were killed by a tsunami with waves up to 90 metres high that hit Nuugaatsiaq in June 2017.

‘Tsunamis triggered by landslides into bays or lakes are fairly common, but it’s rare that they’re this extreme,’ explains Bretwood Higman, co-author of a study documenting the Taan Fjord tsunami. He highlights the unique circumstances required for incidents such as Taan to occur – specifically landslides caused by destabilisation in deglaciated mountain environments falling into growing bodies of meltwater – but warns of an increase in frequency. ‘What is clear is that glacial retreat and/or permafrost melt are likely to be strong contributors to these events,’ he continues. ‘We expect that climate change will make this sort of event more likely.’

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