At some point, even in the absence of recent rain, the river will rise and overflow through the roads and into houses. All of this is the work of glacier dynamics several miles away from downtown Juneau.
The flooding is caused by a glacier lake outburst flood that occurs in the Suicide Basin off the side of the 13-mile-long Mendenhall Glacier. Over many months, the basin fills with water from precipitation and glacier melt. As water pressure builds in the lake, it eventually drills through the Mendenhall Glacier and flows downstream, flooding the Mendenhall Valley and impacting the residents of Alaska’s state capital. Locals colloquially refer to the phenomenon, which has occurred every year since 2011, as a jӧkulhlaup, a common Icelandic term for an outburst flood.
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