Glaciers: From victims to sources of disaster

Editor's note: Yang Zhao is the chief editor of CGTN's Sci-Tech section.

Against the backdrop of a changing climate, the story we most often tell about glaciers is one of disappearance.

They are melting. They are retreating. Satellites and cameras record their decline. Glaciers have become one of the most visible victims of global warming.

But the recent disaster in the Himalayas offers a different warning: cross a certain threshold, and a glacier can become something else – the starting point of a chain of disasters.

That is what happened along the China-Nepal border. A rock-and-ice avalanche that began high in the mountains developed into a debris flow within minutes, sweeping through the Gyirong border port downstream.

How does a glacier make this transition – from a victim of climate change to a source of disaster? And can science help us prevent or mitigate the damage?

I spoke with Nie Yong, a disaster expert at the Institute of Mountain Hazards and Environment under the Chinese Academy of Sciences. His answer was sobering: we are becoming increasingly capable of seeing what is happening to glaciers, but we are still far from knowing exactly when one of them is about to fail.

The last mile of disaster prediction

From several powerful typhoons making landfall in China this summer to countdown alerts appearing on people's phones before an earthquake, people in China have grown accustomed to expecting warnings when nature turns dangerous.

That expectation is backed by real investments in science, technology and infrastructure. Earthquakes and typhoons have relatively mature monitoring systems around the world and are among the areas that have received the most investment in disaster monitoring and early warning.

Earthquake early warning, for example, takes advantage of a basic physical difference: electromagnetic signals travel much faster than seismic waves. Once an earthquake occurs, this allows warning information to be transmitted to areas that have not yet been hit by strong shaking, potentially buying people seconds, tens of seconds or, in some cases, longer to react.

However, glacier hazards are different. They do not have monitoring infrastructure on anything like the same scale. Nor do they offer such a clear-cut pathway from detection to warning.

In fact, glacier hazards are not new to scientists. Since the 1950s, glacier collapse events have increased, while since around 2015, extensive cryospheric hazards have continued to be observed across the high mountains of Asia. But many of these events occur in remote, sparsely populated areas, causing relatively limited losses and rarely making headlines.

The first requirement for prediction is continuous monitoring, and installing that monitoring infrastructure in high mountains is itself a formidable undertaking.

Modern early-warning systems are therefore a combination of technologies. Satellites work alongside ground-based instruments: hydrological sensors track changes in river and lake levels; weather stations record temperature and precipitation; ground-motion sensors detect seismic signals; and cameras provide direct visual observation. But in this case, the disaster began inside Nepal, in a high-altitude and extremely difficult-to-access area. Monitoring equipment could not reach the site.

In a place like this, simply knowing that a disaster is about to happen is already a profound scientific challenge.

And even when monitoring equipment is in place, the problem is far from solved.

The harder question is this: when scientists see an "anomaly," is it actually a warning of disaster?

When an anomaly is not a disaster

According to Nie, scientists watching for ice avalanches pay particular attention to indicators such as the development of cracks near the upper reaches of a glacier and unusual changes in the glacier's flow velocity.

But there is a catch.

A glacier is a plastic, continuously moving body. Satellites can detect tiny changes in its position by comparing images taken at different times.

Yet satellite remote sensing has its limits. To measure displacement, scientists need usable images from both before and after an event. In the case of this rock-and-ice avalanche, the initiation happened so quickly that satellites were unlikely to capture the two sets of images needed for a meaningful comparison.

In other words, a monitoring method designed to detect gradual change is not necessarily well suited to a disaster that unfolds almost instantaneously.

And even if scientists detect unusual movement in a glacier, that does not mean an ice avalanche will inevitably follow.

There is no simple one-to-one relationship between an anomaly and a disaster.

This may be the most difficult part of glacier disaster prediction. As Nie explained, after a disaster has occurred, researchers can often look back and identify signals that preceded it. But before the event, the same kinds of anomalies may appear again and again without triggering a disaster.

The challenge is not simply to detect an anomaly. It is to know which anomaly will become a disaster.

What does seven minutes mean?

In this disaster, only about seven minutes passed between the rock-and-ice avalanche and its impact on the Gyirong Port.

Seven minutes may sound like a reasonable amount of time.

In a rapidly moving disaster descending from a high-altitude mountain into a narrow valley, it is almost no warning at all.

In hindsight, experts believe there may theoretically have been a very short window for warning. But it was not long enough to evacuate people at the border port.

And the geography made escape even harder.

Gyirong lies in a steep mountain valley, where slopes commonly exceed 45 degrees. Even if people had received a warning, moving quickly to higher ground would have been extremely difficult.

This is an important distinction when we talk about early warning.

A warning is useful only if there is enough time – and enough physical space – for people to react.

A chain of disasters

China has conducted three national glacier inventories since 1978. Their assessments show that the area of glaciers across the Qinghai-Xizang Plateau has fallen from about 51,000 to 44,000 and then 39,000 square kilometers – a decline of more than 20%.

Over the same broader period of change, the number and area of glacial lakes on the plateau also increased by more than 20% between 1990 and 2020.

"Glacial lake" is another term that comes up repeatedly in the study of mountain hazards.

The mudslide disaster on August 26 was determined to have been triggered by an ice avalanche. But ice avalanches are not necessarily the most closely watched hazard in this region. In many cases, scientists are more concerned about glacial lake outburst floods (GLOFs).

When a glacier is healthy and advancing, it can act like a bulldozer, pushing rock and debris downslope and building ridges of sediment and rock known as moraines.

As glaciers shrink in a warming climate, meltwater can accumulate behind these moraine ridges, forming lakes.

But not every glacial lake is destined to burst. Nie stresses that only a fraction are considered high-risk.

The danger comes when an external force enters the system.

Across the Himalayas, one of the world's most severe regions for glacial lake outburst floods, many such events are triggered from above: an ice avalanche, rockfall or landslide plunges into a lake, creating a powerful impact that can cause the lake to breach.

One hazard can therefore trigger another.

And the risk can travel far beyond the glacier itself.

A new era of mountain risk

The Himalayas are like a giant wall separating the Qinghai-Xizang Plateau from South Asia.

But this wall has never been impenetrable.

Deep valleys cut through the mountains, opening pathways between two regions. Warm, moisture-laden air travels inland along these valleys. For centuries, traders have followed the same routes, carrying goods, ideas and cultures across the mountains.

These valleys have long been corridors of people-to-people exchange.

Today, those same historical corridors are shared hazard zones. The glaciers hanging above these cross-border valleys share the same thermal stress, the same fragile geology and the same volatile future.

As the planet warms, the hazards born high in the ice are no longer isolated scientific curiosities – they are a swift, shared threat to everyone living in their shadow.