lahar

American  

[lah-hahr] / ˈlɑ hɑr /

noun

Geology.

1. a landslide of wet volcanic debris on the side of a volcano.

2. the deposit left by such a landslide.

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lahar British  

/ ˈlɑːhɑː /

noun

1. a landslide of volcanic debris mixed with water down the sides of a volcano, usually precipitated by heavy rainfall

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lahar Scientific  

/ lä′här′ /

1. A wet mass of volcanic fragments flowing rapidly downhill. Lahars usually contain ash, breccia, and boulders mixed with rainwater or with river or lake water displaced by the lava flow associated with the volcano.

2. The deposit produced by such a flowing mass.

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Etymology

Origin of lahar

1925–30; < Javanese: lahar, lava

Explanation

A lahar is a dangerous combination of mud, rock, and water that flows down the side of a volcano. Some lahars are cause by volcanic eruptions. In geology, the Javanese word lahar is used to describe a specific type of mudflow. Moving down the slopes of a volcano and often flowing into riverbeds, lahars are particularly destructive, described as "rivers of concrete." Like a muddy, rocky avalanche, they grow in size and speed as they move, picking up rocks and debris in their path. An eruption can trigger a lahar, but they're sometimes caused by extremely heavy rain.

Example Sentences

They also warned of potential lahar floods - a type of mud or debris flow of volcanic materials - if heavy rain occurs.

From BBC • Jul. 8, 2025

The rains also triggered volcanic mudslides or lahar in villages surrounding Mount Mayon, an active volcano in Bicol.

From BBC • Oct. 24, 2024

Cold lava, also known as lahar, is a mixture of volcanic material and pebbles that flow down a volcano’s slopes in the rain.

From Seattle Times • May 12, 2024

“At Mount Rainier, large lahars have been associated with eruptions like the Osceola Mudflow,” Westby says, referring to a lahar that happened at the volcano 5,600 years ago.

From Scientific American • Dec. 6, 2022

The water in Spirit Lake would stay put, but glacier melt and groundwater released from an eruption could create a fast-moving lahar.

From "Mountain of Fire" by Rebecca E. F. Barone