``The earthquake has caused instability in the lava dome,'' said Subandriyo, chief of the Merapi volcanology and monitoring office, who goes by a single name.

The rumbling volcano spit out lava and hot clouds Monday morning, sending debris avalanching four kilometers (2 1/2 miles) down the mountain, he said.

Since Saturday's powerful nearby earthquake, the volcano has spewed hot clouds an average of 150 times a day, compared to 50 times before, he said.