Mexico City, Mexico - Mexico's Popocatépetl volcano is keeping up its recent activity, emitting more than 39 exhalations of "low to moderate magnitude" over the last couple of days.

Ash, gases, and steam expelled out of the volcano's crater yesterday morning, reaching well over a mile in the air, according to a statement from Mexico's National Disaster Prevention Center, or Cenapred. The lava dome on "El Popo" - the mound of viscous magma which, being extruded from the crater's vent, dries and piles up not far from it - continued to swell. Overnight, glowing fragments expelled from the inside of the volcano could be seen on its slopes.

According to the Mexican press, one of the most significant emission of ash, steam, and gas occurred yesterday at 7:00 in the morning. The volcano also registered tremors of "high and low frequency" as well as medium-sized micro-tremors occurring as a result of the movement of magma over the course of several hours.

"El Popo," one of several nicknames by which the Popocatépetl volcano is known by nearby residents, is located in Puebla state, about 43 miles southeast of Mexico City. Ash from recent fits of activity in the past few weeks have reached as far as Milpa Alta, one of the southernmost boroughs of the capital.

Authorities raised the alert level on the volcano back to Phase 3 Yellow last Saturday after several weeks of lesser activity. Ash from the volcano had disrupted flights into Mexico City, with over 40 American flights cancelled last week as a consequence of the volcanic ash, which can damage the engines of planes. American Airlines said in a statement that it had cancelled the flights as a precautionary measure, and they were recommenced the next day.

The alert level is one step below Red, which would make necessary an evacuation of the surrounding area. Already it recommends that people stay away from the exclusion zone around the volcano - more than 7 miles away - and suggests that residents in towns in the area wear masks and long-sleeved shirts to prevent inhaling ash expelled the volcano. Cenapred estimates that in the event of an eruption, evacuees would tally up to more than 11,000 people from a total of 18 municipalities residing in the shadow of the volcano.