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.


Brown SK et al., 2017, Volcanic fatalities database: analysis of volcanic threat with distance and victim classification, Journal of Applied Volcanology 6:15

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


Villarrica erupts. March 3, 2015, Chile.


Volcan Villarrica from the air in 2009.


Villarrica (Ruka Pillan in Mapudungun) is one of the most active volcanoes of southern Chile, and is a popular tourist destination in the heart of the Chilean Lake district. Villarrica has been in a continuous state of steady degassing for much of the past 30 years, since the last eruption in 1984-5, and began showing signs of increased unrest (seismicity, and visible activity in the summit crater) in February 2015. Eruptive activity at Villarrica in 1963-4 and 1971 was characterised by vigorous ‘Strombolian’ explosions from the summit – typically with short paroxysms of fire fountaining – followed by the formation of lava flows. The major hazards at Villarrica come from the lahars, which form as a result of the melting of snow and ice from the summit glacier by the intruding or erupting magma. In 1963 and 1971 the lahars that swept off the volcano caused considerable damage, and a number of fatalities in the affected areas.

At the present day, the volume of ice in the summit region is a little over 1 cubic kilometer. Any melt waters and lahars that may form as a consequence of the volcanic activity are expected to drain along any or several of the nine major lahar channels that were either active during the past eruptions of Villarrica, or have been identified from fieldwork and mapping. Recent work on the sediments from Lake Villarrica show that the transport of volcanic ash into the lake by lahars forms a very clear record of the small eruptions of the volcano that would otherwise not be preserved.

Lahar map

Map showing the nine major lahar channels (in blue) that drain off the summit of Villarrica, The area outlined in red shows the extent of the summit glacier field in Februiary 2011. The main tourist resort of Pucon, and lake Villarrica, lie to the north. In 1964, lahars caused  much damage to the village of Conaripe, to the south. Map from Rivera et al. (2015) , lahar channels from Castruccio et al. (2010).

The first Strombolian paroxysm from the 2015 eruption was reported shortly after 3 am local time on 3rd March; and this was followed by reports on social media of spontaneous evacuations from some of the communities that have been affected by lahars in the past. The Chilean agency responsible for civil protection (ONEMI, Oficina Nacional de Emergencia del Ministerio del Interior y Seguridad Pública) declared a ‘red alert‘ shortly afterwards, and SERNAGEOMIN also raised their technical ‘volcanic alert’ level to red. If the current phase of activity follows the pattern of past eruptions, there may be an extended period of elevated activity with intermittent paroxysms over the next few days to weeks.

This paroxysm just lasted a few tens of minutes, but released large puff of ash that rose to about 9 km above sea level and could be seen on geostationary weather satellites; a burp of sulphur dioxide that was visible from space, and coated the summit of Villarrica with a fresh coating of volcanic ‘spatter’.  On the volcano itself, there was clearly some melting of snow and ice, and small amounts of volcanic ash were washed down the local drainages, and into Lake Villarrica.

The footprint of the ‘hotspots’ associated with the freshly deposited ejecta can be seen in the alerts detected by University of Hawaii’s MODIS Thermal Alert System, using imagery from the MODIS sensors onboard NASA’s Terra and Aqua satellites.

MODVOLC screen shot

Screen shot of the ‘thermal alerts’ detected by the HIGP MODIS Thermal Alert System for Villarrica, on 3 March 2015.

Update – March 5th, 2015.

The eruption was over quite quickly, and although a few thousand people evacuated at the time, most returned home later that day. Flights over Villarrica by the volcano monitoring and civil protection teams on March 3rd, and subsequent days, showed that the summit vent became sealed by fresh spatter during the eruption, but signs of activity diminished very quickly. SERNAGEOMIN reported that only one monitoring station was lost during the eruption, and their current scenario is that there may be some intermittent weak Strombolian activity in the near future, which should be readily detectable on the monitoring systems. Photographs posted on social media showed only little evidence for limited damage by lahars during this first eruption; including damage to a tourist centre on the volcano slopes.

Ongoing Activity

Latest status reports from ONEMI, Chile

Latest status reports from SERNAGEOMIN, Chile

Latest webcam images of Villarrica, from SERNAGEOMIN

Latest Volcanic Ash Advisories from the Buenos Aires VAAC

Further information

Great video footage of the 3rd March eruption from 24Horas

Collections of photos and video from BioBioChile24Horas, Cooperativathe Guardian and SERNAGEOMIN.

Villarrica on Volcano Top Trumps

Villarrica pages at the Smithsonian Institution Global Volcanism Programme.


Castruccio, A. et al., 2010, Comparative study of lahars generated by the 1961 and 1971 eruptions of Calbuco and Villarrica volcanoes, Southern Andes of Chile, Journal of Volcanology and Geothermal Research 190, 297-311.

Rivera, A. et al., 2015, Recent changes in total ice volume on Volcan Villarrica, Southern Chile, Natural Hazards 75: 33 – 55

M van Daele, J Moernaut, G Silversmit, S Schmidt, K Fontijn, K Heirman, W Vandoome, M De Clercq, J van Acker, C Wolff, M Pino, R Urrutia, SJ Roberts, L Vincze, M de Batist, 2014, The 600 yr eruptive history of Villarrica volcano (Chile) revealed by annually laminated lake sediments, Geological Society of America, Bulletin doi:10.1130/B30798.1

Friday Field Photo – St Vincent, 1902

Roseau Dry River, St Vincent, 1902. Photo by Tempest Anderson, from Volcanic Studies.

Roseau Dry River, St Vincent, 1902. Photo by Tempest Anderson, published in his book  Volcanic Studies in Many Lands (1903).

Today’s field photo is by Tempest Anderson, of the ‘Roseau Dry River flowing with Boiling Mud’, a picture taken in the aftermath of the May 1902 eruptions of the Soufrière of St Vincent.  The full published caption explains the origins of this boiling mud – a phenomenon we now call a lahar:

This is a small stream in the Wallibu Basin. When the water undermines the banks and the hot ashes fall into the river, the stream is often dammed up, and the giving way of the obstruction is associated with a great discharge of boiling mud. In one of our ascents of the Soufriere, we had crossed the Rozeau Dry River without difficulty in the morning when the weather was fine, but heavy rain had fallen before our return in the afternoon, and the river was full of boiling mud, coming in gushes, as shown in the picture. After some trouble our men cut down two trees which had been killed by the eruptions, and made a bridge by which we crossed. The banks show the characteristic erosion by the rain rills.’

 Lahars are a very common feature at volcanoes, and they may often continue to be triggered by strong rainfall events for months or years after the eruptive activity has ceased.

 Tempest Anderson was an opthalmologist by profession, and also an inveterate traveller and photographer. He accompanied  John Flett to the Caribbean to document the eruptions on St Vincent and Martinique, in 1902, and a selection of his photographs can be found on the website of the Yorkshire Museum. The Soufrière of St Vincent is the centrepiece of the London Volcano project, which runs from 9-13 June.

Further Reading

Anderson and Flett’s Report on the Eruptions of the Soufriere, in St Vincent, in 1902..  Philosophical Transactions of the Royal Society, London, A 200, 353-553 (1903)

Anderson, T., Volcanic Studies in Many Lands, John Murray, 1903.