Galeras is an Andean
The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 in the Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...

n department
Departments of Colombia
Colombia is an unitary republic formed by thirty-two departments and a Capital District . Each department has a Governor and a Department Assembly , elected by popular vote for a four-year period. The governor cannot be re-elected in consecutive periods...

 of Nariño, near the departmental capital Pasto
Pasto, officially San Juan de Pasto, is the capital of the department of Nariño, located in southwest Colombia. The city is located in the "Atriz Valley", on the Andes cordillera, at the foot of the Galeras volcano, at an altitude of 8,290 feet above sea level...

. Its summit rises 4276 metres (14,029 ft) above sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

. It has erupted frequently since the Spanish conquest, with its first historical eruption being recorded on December 7, 1580. A 1993 eruption killed nine people, including six scientists who had descended into the volcano's crater to sample gases. It is currently the most active volcano in Colombia.
Galeras has been an active volcano for at least a million years, with andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...

 as the dominant product.