There were no immediate reports of any injuries or significant damage due to the blast.
People living in danger zones near the volcano were taken to shelters in Pasto, a city located near the border with Ecuador.
A total of about 9,000 people could eventually be forced from their homes if activity within Galeras does not subside soon, officials said.
Residents of Pasto and surrounding villages reported a rain of ash falling on their communities following Friday’s blast.
Galeras is located about 435 miles southwest of Bogota, and is one of 15 active volcanos located across the seismically active country.
An eruption on January 18, 2008, caused nearly 8,000 people from Mapachico and Genoy to flee their homes.
An unexpected and sudden blast in 1993 killed nine people, including six scientists who had descended into the crater to collect gas samples.
Vulcanologists at the Colombia Institute of Geology and Mining said on Saturday that they continue to monitor the nearby Huila volcano, which remains in an orange alert, due to “sizeable” volcanic activity detected in recent weeks.