On Monday, there were at least 28 pyroclastic flows - surges of hot ash and gas that rush down the side of the mountain at high speed.
Gede Suantika, an Indonesian government volcanologist, said there were signs a lava dome was growing on Mount Sinabung.
Lava domes are pile-ups of magma near the vent at the top of a volcano, that have been known to collapse and flow down mountain sides at high speed.