On this day: Kelut erupts, 1919

Mount Kelut (also known as Kelud), situated in the east of the island of Java, is one of the most active and hazardous volcanoes in Indonesia. Over the past six centuries the 1730m volcano has erupted at least thirty times and has been responsible for approximately 15,000 fatalities. On 19 May 1919 it was the site of one of the deadliest volcanic eruptions of the twentieth century, killing over 5100 people when water ejected from the crater lake formed lethal lahars that travelled nearly 40 kilometres and destroyed more than 100 villages.

The 1919 eruption is interesting not only for itself but for the response it generated. At the time Java was under Dutch colonial rule, and the Dutch authorities reacted to the disaster both institutionally, by establishing the forerunner of today’s Indonesian volcanological authority, and technologically, by creating a drainage system intended to manage the hazard posed by the crater lake.

The presence of a substantial crater lake has been the main reason why Kelut is a very lahar-prone volcano, but also significant are its deeply eroded flanks and abundance of loose sediment. During the 19 May 1919 eruption 38 million cubic metres of water was expelled from the crater lake, radiating out through the deep drainage channels and accumulating vast quantities of sediment and volcanic material to produce fast-moving lahars that inundated over 30 square kilometres of the surrounding countryside.

Above: map of Kelut, showing the extent of the 1919 lahars. Adapted from Thouret et al, Bull. Volc., 59:7 (1998), fig. 1.

Even before the 1919 catastrophe the colonial authorities recognized the danger Kelut posed and had, in 1905, constructed a dyke intended to protect the nearby city of Blitar. The 1919 lahars, however, overwhelmed this construction. The Dutch response was to abandon the mitigation of lahars and concentrate instead on preventing them developing by enabling the drainage of the crater lake. The work took until 1926 to complete: a system of seven drainage tunnels was constructed, which reduced the volume of the lake by more than 2 million cubic metres, lowering the level by 50 metres. In 1951 the volcano erupted again, but the successful operation of the drainage system meant that little water was present in the crater and no lahars resulted. A second catastrophe had been averted.

The eruption itself, however, deepened the lake and destroyed the drainage tunnels. Only after another deadly eruption in 1966, in which more than 200 people died, was a new deeper tunnel excavated. The most recent large-scale eruption, in 1990, would certainly have been much more destructive to life and property had the crater lake not been largely drained.

Kelut’s most recent period of restlessness occurred in the autumn of 2007 and resulted in evacuations, although there was no large-scale eruptive activity. A lava dome which has grown since the autumn 2007 eruption now fills the crater lake site (see pictures Université Libre de Bruxelles here; h/t to commenter Hawkeye) and has overwhelmed the drainage inlets.

Information
Global Volcanism Program: Kelut – summary information for Kelut (0603-28=).
Kelud Volcano – information and analysis from the Université Libre de Bruxelles, Belgium (ULB). The volcanic lake specialists at ULB are currently collaborating with the Volcanological Survey of Indonesia in monitoring Kelut.
Le volcan Kelut – account of the 1919 eruption and a detailed history, with illustrations, of the various drainage systems built since to drain the crater lake (in French).