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When the Mountains Let Go · The Climate Translation

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On August 26th, 2026, instruments in the Himalayas detected what looked like an earthquake,
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but it wasn't.
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A massive section of rock and glacier ice had broken loose and plunged more than two
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kilometers into the valley below.
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The resulting collapse caused rock, ice and water to surge downhill.
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River channels were blocked and flooding spread far downstream.
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Mountains may look solid and permanent, but they're filled with cracks, pulled constantly
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by gravity and in high elevations, sometimes held together in part by frozen ground
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and ice.
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So what happens as that ice begins to thaw and glaciers retreat?
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And how much can we actually say about the role climate change played and what happened?
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Welcome back to the podcast, I'm Dr. Mac, and this is the Climate Translation.
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When we look at a mountain, it is easy to imagine one enormous mass of solid rock.
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But that's not really what a mountain is.
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Rocks are filled with cracks, some are tiny, others extend for meters or even hundreds
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of meters through a mountainside.
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Geologists call some of these fractures joints, others may be associated with faults or with
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the boundaries between different layers of rock.
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And those weaknesses matter because gravity is always pulling the mountain downhill.
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Most of the time nothing dramatic happens.
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The rock is strong enough, the slope is stable enough, and the forces holding everything
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in place are greater than the forces trying to move it.
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But that balance can change.
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Water can seep into the cracks.
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Rock can expand and contract as temperatures change, ice can form and melt, and pieces
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of the mountain can slowly weather and weaken.
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And in very high mountains, there's another part of that structure.
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Some of the ground is permanently frozen, we call that permafrost.
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Permafrost doesn't mean the surface is covered with snow or ice all year, it simply means
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that the ground remains at or below freezing for at least two consecutive years.
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And in mountainous regions, that ground may actually be fractured bread rock.
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Water can enter those cracks in the rock and freeze.
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The ice can be part of the structure inside the mountain.
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I've seen some places where they call this frozen glue.
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It's not literally what the ice is doing, but it's a useful way to picture it.
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Imagine a badly cracked concrete wall.
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Now imagine some of those cracks filled with material that helps keep the pieces in place.
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Changing or removing it can change how stable the wall is.
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Glaciers can also affect mountain slopes.
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A large glacier flowing through a valley presses against the rock around it.
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And some locations that ice can provide additional support to the slopes beside it.
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Geologists call this buttressing.
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Think of a book end holding up a row of books upright.
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If you remove it, the balance changes.
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Mountains stability depends on the type of rock, the steepness of the slope, the direction
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of the fractures, the groundwater, the temperature, the erosion, and many other factors.
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But the important idea is this.
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A mountain is not a single solid object.
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It's a complex feature that's developed over millions of years and is constantly responding
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to gravity, water, ice, and temperature.
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Usually those forces remain in balance, but in high mountain environments, some of that
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balance depends on frozen water.
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So what happens when the frozen parts begin to warm?
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Glaciers are always moving, but when a glacier loses more ice than it gains, it becomes thinner
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and begins retreating uphill.
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It's important because as we discussed, a glacier can sometimes provide support to the
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rock beside it.
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As the ice thins and pulls away, that support weakens.
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Imagine removing that book end we talked about.
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The books may not automatically fall over, but the forces acting on them have changed.
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Something similar can happen along a steep mountain slope.
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Then there's the frozen ground inside the mountain.
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At very high elevations, water inside cracks in the rock can remain frozen for years.
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But as temperatures rise, some of that ice begins thawing during the warmer months.
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Now those cracks contain a mixture of frozen ground, liquid water, and open space.
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The structure has become more complicated and potentially less stable.
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Water can move deeper into fractures.
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It can reduce the friction between pieces of rock.
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And in some situations, water pressure inside those cracks can help push blocks of rock
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apart.
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Together, these changes can change the balance that has kept a slope in place.
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And scientists have been measuring exactly these types of changes in central Nepal.
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A study published in 2026 examined temperature and glacier changes across the Langtang catchment,
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a high altitude river basin in the central Himalayas, around the mountain named Langtang Lirung.
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Researchers found that the glacier covered parts of the region warmed by about three
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temps of a degree Celsius per decade between 1960 and 2023.
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It doesn't sound like much, but over several decades, it adds up.
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The researchers also found that glacier loss accelerated substantially after the year
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2000.
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Across the region, glaciers are thinning, breaking into smaller pieces and retreating uphill.
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This glacier had retreated roughly 400 meters between 1990 and 2020.
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Scientists measuring permafrost in the region also found the frozen ground at elevations near
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the collapse side had been actively thawing for years.
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By 2026, Langtang Lirung was no longer the mountain it had been decades earlier.
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The glaciers were retreating, the permafrost was degrading, the meltwater was finding its
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way deep into the rock.
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The melt stability was ultimately governed by what the bedrock was made of, the joint
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orientation and the steepness.
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A compromised rock phase can hold for years before reaching failure, but climate change
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reduced the stability further.
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High temperatures melted the ice wedged in the fractures, degraded the frozen ground,
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acting as subterranean glue and let high pressure meltwater lubricate the fault lines.
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And on August 26th of this year, it collapsed.
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When part of the Langtang Lirung failed on August 26th, the first event was what scientists
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call a rock ice avalanche.
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A huge mass of bedrock broke loose from the glaciated side of the mountain at an elevation
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of around 5,200 meters or 17,000 feet.
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The glaciers sitting above that rock came with it, and gravity took over.
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The mixture of rock and ice dropped thousands of feet into the valley below.
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But what happened next is what made this event so destructive.
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The avalanche didn't simply reach the bottom of a mountain and stop.
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As all of that material moved downhill, it broke apart.
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Ice melted, rock shattered, soil and sediment were picked up along the way.
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Water became mixed with the moving debris.
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And the avalanche began transforming into something more like a debris flow, a thick mixture
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of water, mud, rock, ice, and debris.
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And because it's moving downhill under gravity, it carries enormous amounts of mass, material,
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with it.
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Researchers constructing the event estimate that the debris flow traveled around 22 kilometers
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or 14 miles in only six or seven minutes.
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That means parts of it were moving tremendously fast.
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The flow tore through the river valley, and destroyed the Gyirong border port along
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the Nepal-China border.
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But once again, the disaster didn't stop there.
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All of that debris then entered the river system.
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In some places, rock and sediment temporarily blocked the river.
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Water began collecting behind those blockages.
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And when the water found its way through or around the debris, another hazard developed.
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A flood.
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That flood began moving downstream.
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Researchers estimate the surging water eventually traveled 170 kilometers or more than 100 miles
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through the connected river system.
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At one measuring point farther downstream, the river rose by 9 meters, close to 30 feet.
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All of this happened because the hazards were connected.
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Scientists call this a cascade.
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The easiest way to picture it may be a row of dominoes.
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The first domino is important because it starts the process.
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But the damage farther down the line depends on what each falling domino hits next.
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A mountain collapse can hit a glacier.
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Rock and ice can enter a river.
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Debris can block the river.
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Water builds up.
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And then the flood can travel into communities that may be dozens or even hundreds of miles
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away from the original collapse.
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This is one reason mountain disasters are so difficult to prepare for.
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The people affected downstream may never even see the mountain that failed.
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They may not feel an earthquake.
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They may not even know something has happened upstream.
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They simply see a river beginning to rise.
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And in Nepal, the entire chain from the solid rock highland mountain to the flood water
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far downstream unfolded in a matter of hours.
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So did climate change cause the collapse of the Langtang Lirung?
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Right now, the most scientifically accurate answer is, we don't know.
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Scientists have become quite good at determining how climate change affects some extreme events.
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For a heat wave, for example, researchers can compare today's warmer climate with a
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world without human-caused warming and estimate how much more likely or more intense that
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heat wave became.
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A collapsing mountain side is much harder.
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There are simply way too many individual pieces involved.
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The type of rock matters, the location and direction of the fractures matter, the steepness
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of the slope matters, the water inside the mountain, the amount of ice, and sometimes
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the final trigger may be impossible to identify.
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We have a good example from the same mountain.
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In April of 2015, a magnitude 7.8 earthquake struck Nepal.
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The shaking triggered an enormous avalanche of rock and snow and ice from the Langtang
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Lirung that buried much of the Langtang village and killed hundreds of people.
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In that case, we know what pulled the trigger.
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The earthquake shook an already steep mountain until material broke loose.
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But the August 2026 collapse was different.
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There was no large earthquake first.
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In fact, the falling mountain produced such a powerful seismic signal, it was initially
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mistaken for an earthquake.
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Something on the slope itself reached a breaking point.
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Exactly why it failed, at that particular moment, may take scientists months or even
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years to understand.
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But we do know something about the environment in which it happened.
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The region has been warming for decades.
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Glaciers had been shrinking.
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Permafrost has been thawing, and the glaciers at the collapse site had retreated hundreds
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of meters.
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Researchers also found in the days immediately before the disaster that it included some
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of the warmest August conditions recorded in the area.
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But none of those facts prove that climate change caused this particular collapse.
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But they do tell us that the background conditions of the mountain are changing.
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Think about a wooden deck slowly deteriorating outdoors.
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Rain gets into it, boards expand and contract, the wood begins to rot.
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Eventually someone steps on a particular board and it breaks.
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You might be able to identify the final step, but understanding exactly why the board
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failed also means understanding every variable, everything that weakened it beforehand.
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That is closer to the question scientists are asking in the Himalayas.
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Climate change did not create the steep slopes.
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It didn't create the fractured rock, and the mountains were collapsing long before humans
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warmed the atmosphere.
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But our warming is changing glaciers, it is changing the frozen ground, and the movement
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of water through the mountains.
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Those changes can influence how stable the slopes are.
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So the scientifically responsible conclusion is not that climate change knocked down the
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Langtang Lirung.
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It's that climate change is altering the mountain environment in ways known to affect
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slope stability.
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And that fact matters far beyond this one disaster.
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Nearly two billion people depend on some way on water originating in this area of the Himalayas.
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Communities, roads, bridges, hydropower facilities, and entire river valleys sit downstream
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from the rapidly changing mountain terrain.
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We may never be able to predict the exact moment when a particular slope will fail,
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but satellites can watch slopes move, sensors can measure thawing permafrost, seismometers
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can detect collapses, and river gauges can provide warnings as flood waves move downstream.
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It comes down to this, and a warming world, understanding when a mountain might let go,
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is only one part of the challenge.
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We also have to understand what's coming next.
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To us, mountains look permanent.
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We spend a lifetime in their shadow, and they seem fixed and carved in places forever.
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But they're never truly still.
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Rock fractures, ice shifts, and melt water constantly finds its way into cracks.
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That change doesn't invent these forces, but it does change the rules they play by.
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For decades, those shifts can be small, almost invisible, and then in a matter of seconds,
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an entire mountain can give way.
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What happened in Nepal shows us that a warming world isn't just about rising thermometers,
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and stronger storms, or retreating glaciers.
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Sometimes the real disruption is happening deep inside the bedrock itself.
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I'm Dr. Mac, and this has been the Climate Translation.
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If you have a question about the climate you've been too afraid to ask, or if you have
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a differing opinion, I want to hear from you.
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I can use your viewpoints in future episodes.
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You can reach me at theclimatetranslation at gmail.com.
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I'll see you next time.