Lahar: Lost in translation?

Lahar: Lost in translation?

Since late September, the eyes of the volcano world have turned to Gunung Agung. This prominent volcano in Bali last erupted in 1963, when it released enough sulphur dioxide to form a global stratospheric sulphate aerosol layer that led to vivid sunsets, and short-term global cooling. The 1963 eruption was one of the largest and deadliest in Indonesia in the 20th century; and many of the casualties were caught up in the violent pyroclastic flows and mudflows, or lahars, that swept down the flanks of the volcano in March and May 1963.

Even though the eruptive activity at Agung is currently at a low level, the immediate hazard is once again due to the lahars – slurries of ash and water, that may form during heavy rain, and run rapidly down the volcanic flanks. Lahars have already featured prominently in English language news reports; with some described as ‘cold lava‘. Cold lava, it turns out, is the ‘Google translate’ rendering of the phrase lahar dingin, from some reports of the activity. The problem is not one of Google’s making – but goes back to the way the word ended up in English usage.

Lahar is one of the few words from Javanese that has entered the English language. The Oxford English Dictionary entry for lahar describes it as a ‘destructive mudflow on the slopes of a volcano’; originating in the 1920’s. A contemporary Indonesian – English dictionary offers two translations for the Indonesian word lahar – 1, lava; 2 mudflow. Older dictionaries have only the first rendering of lahar, meaning lava.  Although this isn’t reflected in English dictionaries, lahar was a geographical term familiar to Dutch colonialists in Java by the mid-19th Century.

The botanist and geologist Franz Junghuhn used the term lahar to describe the ravines on the slopes of Kelud, Java (Junghuhn, 1854). In reports of the January 1864 eruption of Kelud, Colonel Versteeg, of the engineering corps of the Dutch colonial army, describes how his workmen shouted “lahar is coming“, shortly before a hot stream of ash and water swept by (Versteeg, 1864). John Hageman experienced the same eruption ‘We heard a thunderous roar approaching .. and a moment later the sizzling fluid rolled by‘.  At Kelud, these destructive flows formed when the  eruption emptied the summit crater lake ‘in a single shock; and the water mixed with sand and stones flowed .. to the south-west and north-west along the so-called Lahars or ravines.‘ So, while lahar is only ever used in English as a technical term to describe a particular sort of flow; its non-technical meaning in Indonesian is clearly rather broader.

The use of lahar to mean a ‘flow of volcaniclastic debris and water’ first came into use in volcanology in the early 1920’s, following another eruption of Kelud in 1919. This eruption caused a terrible loss of life as the crater lake failed, sending cascades of lahars down the ravines that drained the flanks of the volcano. These flows and their deposits were described by the geologist Georg Kemmerling in 1921. Kemmerling distinguished hot (eruptive) and cold (non eruptive) lahars; and recognised that their deposits were dominated by sand-sized material, rather than mud. The next year Berend Escher (brother of the artist, M C Escher) compared the lahars of Kelud to the newly-described deposits of the Valley of Ten Thousand Smokes, emplaced during the 1912 eruption of Novarupta (Alaska). British Geologist John Brooke Scrivenor wrote a short account of the Kelud lahars in 1929; and the term later gained widespread use in volcanology after the 1940’s.

Globally, lahars are one of the most significant hazards posed by volcanoes, due to their capacity to rapidly inundate areas many tens of kilometres from the erupting volcano; while the threat from lahars may continue long after an eruption has ceased. We can only hope that the preventative measures taken around Agung are sufficient to reduce the threats from lahars to those living nearby.


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Escher, BG, 1922, On the hot ‘lahar’ (mud flow) of the Valley of Ten Thousand Smokes, Alaska, Koninklijke Nederlandse Akademie van Wetenschappen, 24, 282-293.

Hageman, J, 1865, Bijdragen tot de kennis der uitbarsting van den Keloed op 3 Januarij 1864, Natuurkundig tijdschrift voor Nederlandsch Indië, 28, 475. [in Dutch].

Kemmerling, GLL, 1921, De uitbarsting van den G. Keloet in den nacht van den 19den op den 20sten Mei 1919: Dienst van het Mijnwezen in Nederlandsch Oost Indie, Vulkanol, Mededeel., 2, 120 p. [in Dutch].

Meinel, AB & MP Meinel, 1967, Volcanic Sunset-Glow Stratum: Origin, Science 155, 189

Pierson, TC, NJ Wood, CL Driedger, 2014, Reducing risk from lahar hazards: concepts, case studies, and roles for scientists, Journal of Applied Volcanology 3:16

Rigg, J, 1862, A dictionary of the Sunda language of Java, Verhandelingen van het Bataviaasch Genootschap van Kunsten en Wetenschappen, Deel XXIX.

Versteeg, WF, 1864, Vervolg op de Aanteekeningen omtrent aardbevingen in den indischen archipel, 27, 129. [in Dutch].

Zen, MT & D Hadikusumo, 1964, Preliminary report on the 1963 eruption of Mt Agung in Bali (Indonesia), Bull Volcanique 27, 269-299


David Pyle is a volcanologist, and Professor of Earth Sciences at the University of Oxford. His first encounter with volcanoes was at the age of 7, when he visited Villarrica, Chile, shortly after an eruption. David studied geological sciences at the University of Cambridge, and later completed a PhD on the 'older' eruptions of Santorini, Greece. After a short post-doc at the California Institute of Technology, David returned to a lectureship in Cambridge. In 2006, he moved to his current post in Oxford. David tweets at @davidmpyle

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