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Last month Seb Watt (from Birmingham Uni) and I went to Indonesia to sample explosive and effusive rocks from two active volcanoes: Mt Kelud (aka Kelut), east Java and Mt Rinjani, Lombok as part of my Alexander Von Humboldt fellowship project to understand what makes volcanoes ‘blow’ or ‘flow’. Here are some thoughts on our fieldwork and Indonesia’s volcanic hazards.
Java is busy - there’s no way around it, I guess we were expecting this to some degree but not perhaps around such a notoriously explosive volcano. Mt Kelud is a small (~1000 m high), unassuming looking volcano. In fact as a result of the thick air pollution and vast built-up area, we could not even see the edifice until about 5 km from the summit. This highly active volcano has a deadly history, killing over 15,000 people in thelast few hundred years, mainly a result of volcanic mudflows (lahars). Interestingly, the word ‘lahar’ is a Javanese word that originates from Kelud volcano, likely after the large 1919 eruption that killed over 5,000 people.
Huge population
I knew the facts before going: 50,000 people live within 10 km of Mt Kelud and over 2 million within 30 km of the volcano. These numbers seemed huge compared to the size of the settlements adjacent to other volcanoes I had visited previously. The biggest difference at Kelud, we realised, is that the land just 5 km away from the volcano is completely flat, especially to the west of the volcano. Houses and intensive farmland cover every inch of land, so that when driving from Indonesia’s second city, Surabaya (>80 km to the north), it was just an endless sprawl of development right up to the volcano.
The island of Java may only be the size of England yet its population is almost three times greater.
2014 explosive eruption
Something else we were expecting to see on the busy Java streets was evidence from last years’ explosive and far-reaching eruption. In February 2014, Mt Kelud erupted violently with a plume reaching to 26 km height (also see Kristiansen et al., 2015). Ash reached Yogyakarta in the south west (~200 km away) and Surabaya in the north east (~80 km away), closing both airports. It was all over in a matter of hours, but was immensely powerful, with recent estimates of eruption intensity of between that of Mt St Helens and Mt Pinatubo (Caudron et al., 2015 GRL), despite the relatively small erupted volume. We based ourselves in Kediri, a city that experienced ~5 cm of ash fall in 2014. However, only a little over a year later, we found hardly any evidence of the eruption. From talking to people in the city, it sounded a like a huge and efficient clean-up operation, lasting about a month, where they had transported all the volcanic material away by train. Even with the estimated 12,000 houses that had experienced roof collapse around Kelud, we only found 1 or 2 houses showing such evidence, the rest had been rebuilt.
The photos above show Ngangtang village (NE of Kelud), which experienced heavy ash fall and roof collapse after the 2014 eruption, evidence of this when we visited it recently a year later was largely absent.
Active volcano, resilient community
Kelud has erupted 7 times in last century alone (2014, 2007, 1990, 1966, 1951, 1920, 1919), so the population around Kelud is used to dealing with volcanic hazards and it is clearly a very resilient region as a result, although not without its problems. The efficient clean-up operation and intensive land-use around the mountain mean that future volcanologists wanting to examine the whole eruption stratigraphy at Kelud may vastly underestimate 2014 eruption due to an absence of deposits. During fieldwork, the Indonesian people were really friendly and happy for us to wander around in their land looking for rocks. Asking the locals about how thick the ash fall was in any particular area with our limited Bahasa Indonesian caused much laughter, and we were often asked to pose in photos with them.
Summit devastation
Closer to the volcano, near the summit region, the devastation of last year’s eruption was clear to see. The original tarmacked road was buried and destroyed, meaning that an unexpected ride on the back of a motorbike was required!
The force of the 2014 explosive eruption, destroyed roads, bent metal poles and scorched vegetation near to the summit area.
Hot and destructive Pyroclastic density currents (PDCs), swept through this region, scorching or removing the dense vegetation that had grown back quickly after last explosive eruption in 1990 (Bourdier et al., 1997). Contrary to the 1990 eruption, the 2014 explosion also destroyed the drainage tunnel that had survived since the 1960s and was used to drain water away from the crater lake, reducing the lahar hazard. Interestingly, the organisation that monitors volcanoes in Indonesia, the Center for Volcanology and Geological Hazard Mitigation (CVGHM), was first established after the disastrous 1919 eruption at Kelud. One of CVGHM’s first tasks was to drill the Kelud drainage tunnel through the crater wall. This ambitious engineering project was one of the first of its kind, a pioneering project for volcanic hazard mitigation. During the explosive eruption last year the lake water vaporised and the hydrothermal system was likely destroyed, so it will take a while before the lake water is restored. Kelud seems to go through these cycles after each explosive eruption.
Images above show crater evolution. In 2007-2008 Keluderupted in a very different way, with a slow-growing lava dome within the volcanic lake. The 2014 eruption completely destroyed this dense lava dome, and huge (3 m) blocks could be seen close to crater rim. Our recent visit in 2015 shows the beginnings of a new lake forming in the crater.
Photos above show a huge part of the 2007 dome ejected 1 km from the crater during the first stages of the 2014 explosive eruption.
Research
My research aims to understand why Kelud sometimes erupts effusively like in 2007 and sometimes explosively like in 2014. The purpose of this fieldwork was to sample rocks from previous effusive and explosive eruptions, taking them back to University of Mainz, Germany and performing petrological experiments on them to determine what state the magma was in before both the explosive and effusive eruptions.
The volcanologists directly saving lives
Before starting our rock sampling, we visited the observatory where volcanologists monitor the volcano at 7 km distance. Their roof was destroyed as a result of heavy pumice fallout during last year’s eruption. The volcanologist we met, Budi Priavola, told us that Kelud is a ‘well behaved volcano’, it generally provides at least a few weeks notice in the form of earthquakes, lake temperature increase and deformation. Before the 2014 eruption they were able to forecast the activity, enabling the authorities to evacuate 100,000 people just a few days prior to the big event. In fact the emergency aid teams were ready and waiting in Kediri (a city ~30 km from the volcano) the day before the explosive eruption. Their accurate prediction likely saved many lives, so although we both call ourselves volcanologists, it was a humbling experience to meet scientists who are directly saving lives based on monitoring data which can often be difficult to interpret.
Kelut observatory. Seb and I with volcanologist Budi Priavola.
Expectations
Contrary to what we were made to believe, Indonesia does not seem to be the school geography case study of a region ill-equipped to deal with volcano hazards. Instead our experience at Kelud demonstrated the presence of innovative mitigation engineering, such as the crater lake drainage tunnels and Sabo dams (used to dissipate the energy from lahars and PDCS), accurate prediction of the timing of the eruptions, efficient evacuation, and a swift recovery following a substantial explosive eruption. These successes are rarely known beyond Indonesia, which is perhaps why we have these views. The communities around Kelud seem to be quite prepared and to be in good hands. Unfortunately there are many volcanoes in Indonesia, (the country with the highest density of volcanoes in the world), and many of these have not erupted in recent history and thus are not monitored. This, coupled with the high population density (especially in Java), means that an unexpected eruption from one of these volcanoes may pose the biggest hazard risk in the future. Indonesia appeared to be a mysterious place before we embarked on our trip, based on how difficult it was to extract information about its volcanoes. But what we found is a dynamic country full of surprises and interesting stories, I hope we can return soon!
The crater of Mt Rinjani, Lombok. This huge caldera (~7 km in diameter) formed in the 1257 AD 'Samalas' eruption, thought to be one of the largest eruptions in the world for 2 thousand years.
The Gilli islands here seen under the wing, while over the wing, the 3765 metre peak of Mt Rinjani can be seen. The Samalas eruption in 1257 deposited up to 1.5 m of volcanic material in the popular tourist destination, the Gilli islands (35 km west of Rinjani). The effect of the Samalas eruption on these tiny, low lying islands (max height ~10 m), perhaps has made them more resilient against rising sea level.
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