Merapi volcano (Java,Indonesia) and Merapi-type Nuée ardente

A particular nuée ardente type (Merapi-type avalanche nuée) has been defined at the Merapi volcano because of its prominent role in the recent activity of the volcano: gravity plays a significant role during the eruption. However, some other eruption styles occur too producing surges and ashfalls. Three types of tephra, deposited in a very short time-span (15 years) are compared: chemistry and mineralogy are similar, but grain-size analyses are different. There is no vesicular glass, and it is concluded that there is an absence of new magma. This example shows clearly the variety of volcanic styles, with similar chemistry in a very short period. Avalanche nuées from collapsed domes or flows are separated into two types:

1. Merapi-typesensu stricto, without any fresh glass, derived from a wholly solidified dome.
2. Arenal-type, containing pumiceous glass, derived from a dome, the interior of which is still liquid.