Lava dome extrusion continued through 1979 from a SW flank vent ~200 m below the summit. A lobe of lava extending a short distance down the upper SW flank gave the dome an asymmetrical form and occasionally spawned nuées ardentes d'avalanche. The last significant nuée ardente traveled ~6 km in August 1979, but remained within the forbidden zone, where human access is prohibited. The maximum thickness of the active dome was ~100 m in October. In November, VSI estimated its volume at 1.14 x 10⁶ m³ and its extrusion rate at ~10⁵ m³/month.

Geological Summary. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: A. Sudradjat and L. Pardyanto, VSI.