The avalanche of rocks created a thin layer of dust that fell on two hamlets located on the western slope of the 2,914-meter (9,560-foot) volcano Friday, said Dewi Sri from the vulcanology office in Yogyakarta.
"It is not an ash rain caused by an emission of deadly hot clouds. The rocks were emitted by Merapi during its last eruption in 2001," Sri told AFP from the ancient royal town located 30 kilometers (18.
5 miles) south of Merapi.
Merapi has been on standby alert for more than two weeks, one level below that which would require a mandatory evacuation for more than 29,000 people living around its fertile slopes.
Merapi's seismic and volcanic activities on Saturday "remains pretty much similar" to recent days, she said.
Officials are monitoring the volcano round-the-clock.
Scientists have warned that the volcano could erupt at any time and hundreds of residents have already been relocated to temporary shelters.
Many people living on the slopes of the volcano have refused to evacuat