Frozen to Flooded

Glaciers are critically important to our world, supplying freshwater to millions of people, sustaining agriculture, and supporting ecosystems. However, due to global warming, glaciers are vanishing at an alarming rate, with projections indicating they could lose 40% of their mass by 2100 (Rounce et al, 2023).

As glaciers retreat, they produce meltwater, which accumulates in unstable proglacial lakes, which can trigger Glacial Lake Outburst Floods. These floods can destroy entire communities, critical infrastructure, and ecosystems downstream, leading to loss of life and economic devastation and have long-term environmental consequences. The increasing frequency of Glacial Lake Outburst Floods highlights the urgency of addressing climate change and implementing measures to mitigate glacial hazards. Around 90 million people across 30 countries live near glacial lakes, with 15 million residing within 50 km of a lake and just 1 km from potential GLOF pathways, putting them at high risk (Taylor et al. 2023).

When a glacier retreats or thins, they leave behind a depression, where meltwater collects. Over time, the meltwater turns into a glacial lake and is retained by a natural dam (terminal moraine or ice core) at the end of the lake.

However, these dams are unstable. As meltwater continues to accumulate, the increasing water pressure weakens the dam, making it more susceptible to failure. A Glacial Lake Outburst Flood occurs when the dam holding the lake suddenly fails due to various triggers including:

• Ice or rock avalanche, or glacial calving
• Heavy rainfall or rapid snowmelt
• Earthquakes or landslides

The Cordillera Blanca Mountain Range is located in seismically active area in Peru. With elevations between 4,000-6,000m above sea level, it is also the highest and most extensive tropical glaciated region in the world - containing 25% of the world's tropical glaciers.

Tropical glaciers are sensitive and respond rapidly to climate fluctuations, making them critical indicators for climate change.

The instability of glaciers in the Cordillera Blanca has caused 24 Glacial Lake Outburst Floods in the last 150 years, resulting in over 6,000 deaths.

Glacial Lake Outburst Floods are not a new phenomenon. However, due to global climate fluctuations, glaciers in the Cordillera Blanca are continuing to shrink at an alarming rate. This trend increases the risk of these events and heightens the exposure and vulnerability of communities living downstream.

Lake Palcacocha is located approximately 20km away from Huaraz. This glacial lake is perhaps the most studied lake in the Cordillera Blanca.

The tropical Andes, where Lake Palcacocha is located, have experienced significant warming. According to research by Vuille et al. (2015), the region has warmed at a rate of approximately 0.1°C to 0.2°C per decade since the 1950s, which is greater than the global average.

Rising temperatures have driven glacial retreat, leading to the expansion of the glacial lake. The video below, using Landsat satellite imagery from 1990 to 2020, illustrates these changes. As the lake grows, the increased water volume puts greater pressure on the dam, heightening the risk and potential impact of a Glacial Lake Outburst Flood.

In 1941, a fatal Glacial Lake Outburst Flood occurred, which destroyed one third of Huaraz and killed approximately 1,800 inhabitants.

Since then, there have been remedial efforts to mitigate the impacts of Glacial Lake Outburst Floods. An artificial dam and temporary tubes/hoses have been installed to siphon off water. These have also been installed in 40 other glacial lakes throughout the region, with methods such as open cuts, artificial dams and tunnels (Emmer et al., 2018). Ultimately, this is to help to mitigate risk, by slowing the growth of the lakes and ultimately prevent Glacial Lake Outburst Floods from occurring.

Lake Palcacocha has even become the subject of an  international court case . Saúl Luciano Lliuya, a Peruvian farmer and mountain guide, along with over 50,000 residents of Huaraz, faces a severe flood risk from a glacial lake swollen by climate change. Fearing a potential disaster, he sued the energy giant RWE in 2015, arguing that as a major CO₂ emitter, the company bears partial responsibility for the threat endangering his community.

Glaciers are melting rapidly due to global warming, creating unstable glacial lakes that pose a significant risk of Glacial Lake Outburst Floods, which can devastate communities and ecosystems downstream. Around 90 million people across 30 countries live near these lakes, with 15 million at high risk, especially those within 50 km of a glacial lake. In the Cordillera Blanca mountain range in Peru, Lake Palcacocha is a major concern for Huaraz, a city that has faced the destructive impact of GLOFs in the past, including a fatal flood in 1941 that killed around 1,800 people. Efforts to mitigate risks, such as artificial dams and water siphoning, aim to control the growth of glacial lakes above Huaraz. However, ongoing glacier retreat and the unpredictability of these lakes, worsened by climate change, raise concerns about whether current measures are sufficient to prevent another disaster like the 1941 flood.