You probably didn't feel anything yesterday, but the mountain was very, very active. Much of the afternoon and evening was spent on a roller coaster of microtremors and low frequency quakes, all of which had the potential to result in a sizable eruption. But did not. Yet.

The volcano now has a voice, and yesterday it was heard grumbling deep inside with a few loud booms.

NASA satellite readings indicate that the lava in the crater that generated 51 Megawatts of energy three days ago has nearly doubled and is now generating 97 Megawatts.

A 3.1SR shallow quake was registered on the east slope of the mountain yesterday a bit after 8 p.m.

The local press quotes PVMBG as saying the sulfur dioxide (SO2) concentrations are very high, around 2000-3000 ppm compared to 1000 ppm experienced during Merapi's last eruption.

PVMBG says that if the indicators continue in their current trends (basically, everything increasing), we should expect a larger eruption. As usual, they are very careful in their language.

The airport reopened yesterday afternoon, and remains open this morning.

Text by Jackie Pomerov, Picture by Suresh Melwani