Bursting ice dam in Alaska highlights risks of glacial flooding around the globe

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The collapse of a gray, two-story house with white trim and its subsequent descent into the river below, accompanied by a floating piece of its roof, highlighted the aftermath of a ruptured glacial dam in Alaska’s capital. The torrential waters also caused a neighboring condo building to perch precariously on the brink, as erosion had already eroded its foundation. This calamity occurred over the weekend due to the bursting of a glacial dam, known as a jökuhlaup, which is a relatively unfamiliar phenomenon in the United States. However, researchers underscore the global risk posed by such glacial floods, potentially endangering around 15 million individuals worldwide.

Amanda Arra, whose house was left dangling perilously over the river bank, recounted how she watched trees tumble into the water, fueling her unease as the destructive scene unfolded. The flood event in Juneau originated from a lateral basin of the impressive Mendenhall Glacier, which serves as a barrier for rain and snowmelt that accumulates in the basin during the warmer seasons. Ultimately, the water surged from beneath the glacier and flowed through Mendenhall Lake, continuing its course down the Mendenhall River.

Although water releases from the basin have sporadically led to flooding since 2011, they typically occur more gradually over several days, as explained by Eran Hood, an environmental science professor at the University of Alaska Southeast. The uniqueness of Saturday’s incident lay in the rapidity of the water surge, causing the river’s flow to increase to approximately 1.5 times the previous highest recorded level. This deluge was so forceful that it swept away research sensors meant to study the glacial outburst phenomenon.

The aftermath of the event resulted in the complete loss of two homes and partial damage to a third, according to Robert Barr, Juneau’s deputy city manager. Fortunately, there were no reported casualties. Eight buildings, including those that succumbed to the water’s force, were declared uninhabitable, though some might be salvageable with significant repairs or bank stabilization efforts. Others suffered lesser degrees of harm.

While global climate change contributes to the melting of glaciers such as the Mendenhall, its relationship to these types of floods is intricate and multifaceted. The basin where rain and meltwater gather was previously covered by the Suicide Glacier, which used to flow into the Mendenhall Glacier, providing it with ice. However, as the climate has warmed, the Suicide Glacier has retreated, leaving a lake in the basin blocked by the Mendenhall.

The connection between climate change and the overarching phenomenon is evident, but the erratic ways in which these waters breach ice dams and trigger downstream floods are not entirely attributable to climate change. Researchers highlight that while climate change is a causal factor in the overall phenomenon, it does not directly induce each individual flood event.

The unpredictability in terms of timing and water volume in these flood events presents challenges in preparation, according to Celeste Labedz, an environmental seismologist at the University of Calgary. More than half of the people at risk from glacial outburst floods are concentrated in four countries: India, Pakistan, Peru, and China, as indicated by a study published in Nature Communications in the present year.

Though glacial outburst floods are linked to climate change, the distinctive ways in which they unfold and their subsequent impact are shaped by complex factors. The vulnerability of the ground along the Mendenhall River, composed primarily of loose glacial deposits, makes it particularly susceptible to erosion. Had the flood coincided with heavy rainfall, the damage could have been even more extensive. Residents like Chris and Bob Winter, whose house flooded for the first time in 2014 and again during the recent event, are grappling with significant losses and uncertainty about the future. The occurrence emphasizes the critical need for understanding and managing the consequences of glacial melt and the potential for subsequent floods on a global scale.

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