Overview of the 2006 Eruption of Mt. Merapi

Antonius Ratdomopurbo, François Beauducel, Joko Subandriyo, I.G. Made Agung Nandaka, Christopher G. Newhall, Suharna, Dewi Sayudi, Heru Suparwaka, Sunarta

J. Volcanol. Geotherm. Res., doi: 10.1016/j.jvolgeores.2013.03.019, in press, 2013.

Abstract. In the last part of the 20th century and the beginning of the 21st century, Mt. Merapi in Central-Java Indonesia erupted about every 2-5 years. Most of the eruptions were low in explosivity, with VEI-3 or less. Eruptions usually involve formation of a lava dome, either in the beginning or in the end of the eruptive episode.
For the 2006 eruption, the precursory signal was first observed in the middle of the year 2005 with a decrease in EDM slope distances to points on the rim, an increase of seismicity and a possible increase of SO2 emissions. Those early events marked the beginning of a more continuous period of inflation, which led to the eruption.
In total, the pre-eruption displacement of the southern rim reached at least 2.4 m toward the measuring station in Kaliurang (KAL). From late April until June 2006, a lava dome grew on the summit with a volume that gradually increased until it reached about 4.1 million m3 in 38 days. The total of erupted magma was about 5.3 million m3 dense-rock-equivalent (DRE). The dome subsequently collapsed in three steps from June 4 to June 14, leaving an open scar on its southeast side. In this paper we detail changes of dome morphology that were monitored by taking successive photographs from similar positions. The eruption in 2006 marked a significant change in summit morphology, from west-southwestward opening during the 20th century to the currently southeast orientation. Also, an Mw 6.4 earthquake occurred on 26 May, midway through the eruption, which adds interesting questions about the relationship of the eruption and the earthquake.
EDM data from 2006 and previous eruptions show that the summit remains inflated after each eruption, i.e., no significant deflation occurs following eruptions. The lack of post-eruption deflation suggests that magma remains in the shallow parts of the edifice after the eruption. As a result, the complex of summit lava domes and their intrusive roots grow with time and Merapi¿s rim and summit become progressively more unstable and prone to collapse.