Alaska’s Second Largest Megatsunami Reveals Climate Change Peril

A massive megatsunami that swept across a remote Alaskan fjord during summer 2025 has been confirmed to be the second biggest wave of its kind ever recorded, serving as a stark warning about the dangers of climate change. The enormous wave, which stood at approximately 500 metres in height, was triggered when 64 million cubic metres of rock – matching the volume of 24 Great Pyramids – suddenly collapsed into Tracy Arm Fjord in southeast Alaska in the early morning of August 2025. Scientists say the event barely escaped disaster, as tourist ships that routinely pass through the beautiful water passage might have been trapped in the devastation had the mountainside failure occurred during daylight hours. New research indicates that faster-melting glaciers caused by climate change is weakening mountainsides across Alaska, creating conditions for such massive failures in the coming decades.

The August 2025 Catastrophe

The megatsunami impacted Tracy Arm Fjord in the early morning of August 2025, when a massive section of mountainside abruptly collapsed and fell into the water below. The sheer volume of rock – 64 million cubic metres – hit the fjord with such tremendous force that it shifted an vast quantity of water, creating a wave that soared to nearly 500 metres in height. Dr Bretwood Higman, an Alaskan geologist who travelled to the location weeks after the event, described the scene as one of complete destruction, with broken trees strewn over the mountainside and vast swathes of bare rock stripped bare of soil and vegetation.

The moment of the disaster proved fortuitous for the numerous visitors who visit Tracy Arm Fjord annually on cruise vessels. Had the landslide occurred when it was light when vessels usually travel through the waterway, the results could have been catastrophic. Dr Higman spoke about the fortunate avoidance, stating that “there were people that were very nearly in the hazardous position” and voicing serious worry about future events. His words underscore the serious risk posed by Alaska’s volatile geology and the rising rate of such collapses.

• Equivalent to 24 Great Pyramids of stone collapsed into the fjord
• Wave reached nearly 500 metres in height, second-biggest megatsunami ever
• Occurred during early morning hours, sidestepping populated cruise ship traffic
• Scientists caution climate change is hastening similar mountainside collapses

Understanding Megatsunamis and The Mechanics

Megatsunamis are a distinct and particularly destructive phenomenon, fundamentally different from the dominant tsunamis in headlines. Unlike their oceanic counterparts, which are caused by seismic events or subaquatic volcanic activity and can travel thousands of miles across open water, megatsunamis are localised events resulting from abrupt, substantial shifts of water. They occur when landslides triggered by seismic activity or by unstable rock formations – surge into enclosed water bodies such as fjords, lakes or narrow coastal inlets. The enormous volume and speed of material entering the water produces an enormous wave that breaks down quite rapidly within the enclosed space.

The contrast between these two tsunami types is essential for understanding coastal hazard management. Traditional tsunamis, exemplified by the catastrophic 2011 Japan earthquake, can travel through entire ocean basins and strike populated coastlines thousands of miles away, causing numerous lives. Megatsunamis, in comparison, impact only limited regions immediately surrounding the impact zone. However, this does not reduce their destructive power – within their limited geographical range, megatsunamis can be remarkably powerful, with waves attaining heights that dwarf those created by distant earthquakes. The Tracy Arm event shows clearly how dangerous these localised events can be.

How Megatsunamis Develop

The method behind megatsunami formation is simple but terrifying in its execution. When a substantial volume of rock or debris rapidly separates from a mountain slope and plunges into water below, it moves an vast quantity of liquid in an remarkably compressed timeframe – often in just seconds or minutes. This quick shift creates a wave that attains extraordinary heights, constrained by the local topography of the fjord or inlet. The August 2025 event saw 64 million cubic metres of rock – equivalent to 24 Great Pyramids – plunge into Tracy Arm Fjord in under a minute, creating the near-500-metre wave that ravaged the area.

Alaska’s landscape makes it particularly vulnerable to these major disasters. The region’s steep mountainsides, narrow fjords and frequent seismic activity establish perfect circumstances for extreme wave formation. Precarious geological structures situated above submerged basins require only the slightest destabilisation to trigger collapse. Historically, earthquakes have provided the primary catalyst, but researchers increasingly acknowledge that glacial recession is uncovering previously stable rock faces to fresh strain, substantially transforming the equilibrium balance across the Alaskan geography.

• Concentrated waves resulting from landslides flowing into restricted water systems
• Diminish quickly in confined areas in contrast to transoceanic tsunamis
• Can attain elevations surpassing 500 metres near impact zones

Glacial Recession and Accelerating Risk

The August 2025 megatsunami has revealed a concerning connection between climate change and geological upheaval in Alaska. For decades, massive glaciers acted as natural buttresses, their mass and icy composition helping to stabilise vulnerable rock structures perched on mountainsides. As worldwide temperatures increase, these glaciers are receding at extraordinary pace, exposing bare cliff faces that have lost their critical support systems. Dr Stephen Hicks of University College London explains that the glacier at Tracy Arm “previously helped to prop up this piece of rock”, but as the ice vanished, it took away the support mechanism that had kept the mountainside intact for centuries.

This process creates a cascading sequence of geological consequences. When glacier ice withdraws, it not merely eliminates physical support but also modifies water pressure dynamics within the rock face and transforms drainage patterns that had formerly maintained stability. The exposed bedrock turns exposed to weathering, seismic vibrations and weight-induced strain that it had been insulated from for millennia. Scientists express concern that Alaska’s quickly thawing glaciers are preparing countless mountainsides for massive collapse, transforming the region into an increasingly hazardous landscape where megatsunamis may become distressingly common occurrences rather than uncommon natural events.

Global Warming as a Trigger

Research published in the journal Science clearly establishes that climate-driven glacier melt is fundamentally reshaping Alaska’s geological hazard profile. The team conducting the Tracy Arm investigation integrated field observations, seismic data and satellite imagery to piece together the sequence of events leading to the August 2025 collapse. Their analysis reveals that glacier retreat was the primary factor destabilising the rock formation, exposing the cliff base and eliminating the ice’s supporting pressure. This research suggests that similar vulnerable formations exist throughout southeast Alaska, each capable of being triggered into collapse as their glacial anchors keep disappearing.

The consequences are deeply worrying for both the local ecological systems and people living in the area. As rising temperatures drive glacier retreat across Alaska, the timeframe for preventing future megatsunamis is rapidly closing. Scientists emphasise that this is not a problem confined to one location confined to Tracy Arm Fjord – it signals a region-wide threat threatening numerous fjords and coastal areas. The timing of the August 2025 event, taking place during the pre-dawn period when tourist vessels were not present, was fortunate. Dr Bretwood Higman cautioned that “we’re not going to be so lucky in the coming years”, underscoring the pressing requirement for enhanced monitoring and advance alert mechanisms before the next major failure happens.

Safety Concerns and Future Preparedness

The Tracy Arm megatsunami has uncovered a significant gap in Alaska’s tourist facilities and waterfront settlements. With substantial numbers of tourists exploring southeast Alaska’s fjords every year, the narrow window of safety that shielded vessels during the August 2025 event cannot be relied upon long-term. Scientists caution that further collapses may occur during daytime when visitor numbers is heaviest, possibly causing severe loss of life. The remote location and challenging terrain of Tracy Arm Fjord would greatly hinder emergency response and rescue efforts, worsening the disaster’s consequences on those affected and recovery work.

Current monitoring systems in Alaska continue to be inadequate for detecting imminent megatsunami risks across the region’s numerous vulnerable fjords. Developing extensive alert networks requires substantial funding in earthquake detection equipment, satellite monitoring technology and immediate information processing capabilities. Researchers emphasise that improved monitoring of cliff faces backed by glaciers could provide vital early warning of dangerous destabilisation. However, the speed at which these collapses can occur—often within seconds—means that effective warning systems must be linked to emergency procedures and public education campaigns to ensure swift responses when danger emerges.

• Install live seismic monitoring stations throughout Alaska’s fjord systems and glacier-fronted coastlines
• Develop evacuation protocols and warning systems for cruise operators and shoreline populations
• Conduct regular geological surveys to identify additional unstable rock formations in high-hazard zones
• Establish international collaboration on megatsunami research and climate-related coastal hazard assessment

Sector Reaction

Alaska’s passenger vessel industry has begun reassessing operational procedures following the Tracy Arm incident. Tour operators are implementing additional safety protocols, including adjusted timetables to avoid maximum tsunami risk periods and improved liaison with geological monitoring bodies. However, industry spokespeople recognise that complete avoidance of affected areas may be financially unfeasible due to their appeal to tourists looking for unspoilt Alaskan wilderness. The challenge lies in reconciling business priorities with traveller protection whilst climate-driven geological hazards continue escalating across the area’s most picturesque destinations.