Here's a Mexican government website that provides up-to-date scientific data on Popo's eruption.
The 17,000-foot volcano, whose name is the Aztec word for smoking mountain, was dormant for nearly 50 years in the mid-to-late 20th Century. It suddenly awakened in 1994, and since then has erupted numerous times, including several times earlier this year.
UPI reports that officials have warned nearby residents to avoid the area around the volcano, and that falling ash may affect nearby towns.
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In 1522, Spanish invader Hernán Cortés's men were the first non-natives to scale the volcano. They did it in an effort to find sulfur for the manufacture of gunpowder.
Colima, which is directly to the west of Popo, has erupted more than 40 times since 1576. Though it shares a name with the Mexican state of Colima, most of its surface area actually lies in the neighboring state of Jalisco. It erupts frequently, and a 2014 eruption sent ash about 3 miles in the air.