Santa Maria is part of the Sierra Madre volcano range located in Guatemala. It first began erupting 30,000 years ago. It is a stratovolcano whose peak towers about 4,600 feet above the nearby city of Quetzaltenango. Its eruption in 1902 was the second-largest volcanic eruption of the 20th century and the fifth-largest in the past two to three centuries. The volcano Santiaguito is connected to Santa Maria.
As a cone-shaped mountain, Santa Maria spews both basalt and andesite lavas.The 1902 eruption, which ended a period of at least 500 years of dormancy, lasted 19 days and produced an ash cloud estimated at 16 miles in height. At least 5,000 people died as a direct result of the eruption, with more killed by the malaria outbreak that followed.
The twin peak of Santiaguito, which formed in a crater left by the 1902 eruption and shares its interior structure with Santa Maria, erupted in 1922 and has been considered active ever since. When Santiaguito's dome partially collapsed in 1929, fatality estimates ranged from several hundred to several thousand. Although lava flows seldom occur, damage from landslides known as lahars have repeatedly destroyed nearby towns and infrastructure. Geologists fear that Santiaguito may collapse, causing additional hazardous landslides.