Alaska’s near-record landslide tsunami sent a wave 1,580 feet up the fjord walls – and left clues for building a warning system

nature & planetanalysisThe Conversation2025 · Tracy Arm, Alaska, USA

Alaska’s near-record landslide tsunami sent a wave 1,580 feet up the fjord walls – and left clues for building a warning system

the gist

On August 9, 2025, a mountainside above Tracy Arm, a fjord in Alaska, collapsed into the water, creating the second-highest tsunami in recorded history. The wave ran up the opposite fjord wall to 1,580 feet, higher than the top of Taipei 101. Landslides like this are becoming more common where glaciers retreat from steep, rising mountains, because the ice had been holding the slopes in place. The collapse was preceded by a rise in small seismic tremors that could have served as a warning. Researchers argue that an alert system, like those used for avalanches, could have given ships and towns time to respond.

how it works

Glaciers at the base of steep mountains provide support, and as they melt back, rock becomes unstable. When millions of tons of rock hit the water, the momentum transfers into the water and forms a tsunami. Rain seeping into cracks adds pressure that can push a slope toward failure.

so what

Warming-driven glacier retreat is opening new landslide and tsunami hazards in Arctic fjords, which are popular with cruise ships. Alert systems offer a way to manage risk without banning visits.

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background

Tracy Arm is a fjord in the U.S. state of Alaska near Juneau (outlet at 57° 46' 40" N 133° 37' 0" W). It is named after Secretary of the Navy Benjamin F. Tracy (1889–93). It is located about 45 miles (72 km) south of Juneau and 70 miles (110 km) north of Petersburg, Alaska, off of Holkham Bay and adjacent to Stephens Passage within the Tongass National Forest. Tracy Arm is the heart of the Tracy Arm-Fords Terror Wilderness, designated by the United States Congress in 1990.

Tracy Arm-Fords Terror Wilderness contains 653,179 acres (2,643.32 km2) and consists of two deep and narrow fjords: Tracy Arm and Endicott Arm. Both fjords are over 30 miles (48 km) long and one-fifth of their area is covered in ice. During the summer, the fjords have considerable floating ice ranging from hand-sized to pieces as large as a three-story building. During the most recent glaciated period, both fjords were filled with active glaciers

From Wikipedia: Tracy Arm (CC BY-SA 4.0) ↗ · text CC BY-SA 4.0

see

Wknight94, CC BY-SA 3.0, via Wikimedia Commons

Dankarl, CC BY-SA 4.0, via Wikimedia Commons

U.S. Geological Survey/John Lyons, Public domain, via Wikimedia Commons

Illustrative photo · U.S. Geological Survey/John Lyons, Public domain, via Wikimedia Commons

source: The Conversation ↗

politics

Trump and Netanyahu reportedly clash over whether to resume military action against Iran

the gist

Israeli reports also say the cabinet directed the military to prepare for a possible new attack on Iran.

so what

The United States and Israel have been closely aligned on Iran's nuclear programme and regional threats, so open disagreement between their leaders over military strategy is unusual and closely watched. Whether to resume strikes is a decision with consequences for shipping, oil markets and the wider Middle East.

fun fact

Benjamin Netanyahu has served as Prime Minister of Israel for more years in total than any other person.

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Data: GDELT Project

Illustrative photo · Israel Belkind and Fanny Abramovitch (original) “The Provis…, Public domain, via Wikimedia Commons

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supplementary video · Epimetheus on YouTube ↗

world cultures & travelWikivoyageclassic9th–15th century · Siem Reap, Cambodia

Angkor was the largest pre-industrial city on Earth, covering about 3,000 square kilometres

the gist

Angkor, near Siem Reap in northern Cambodia, was the capital of the Khmer Empire, which ruled much of mainland Southeast Asia between roughly the 9th and 15th centuries. At its height the city spread across about 3,000 square kilometres, making it the largest pre-industrial city on Earth by area. Its growth depended on water: huge reservoirs called barays, along with canals and embankments, stored monsoon rain and carried it to rice fields. That system let farmers harvest more than once a year and fed a very large population through the dry season. The temple complex of Angkor Wat, built in the early 12th century, is the best-known monument and still stands at the heart of the park.

how it works

The Khmer kings built enormous rectangular reservoirs that caught monsoon rain during the wet season. Earthen dykes and canals moved that water into rice paddies, so farmers could grow crops across much of the year. The surplus food supported craftsmen, builders and the workforce that raised the temples.

so what

Angkor shows how a society without industrial machinery could build a city on a scale that rivals modern metropolises, using engineering and water management instead. Some historians link its decline to drought, flooding and shifts in its water systems, which makes it a long-running case study in how cities depend on managing water. The site is a UNESCO World Heritage Site and one of the most important archaeological landscapes in Southeast Asia.

fun fact

The outline of Angkor Wat appears on the national flag of Cambodia.