April 18 Update: CENAPRED has raised the Popocatepetl volcano alert level in Puebla, Mexico and areas South of Mexico City due to increasing activity. The eruption alert is now at Phase 5 on a 7-step warning scale, prompting schools to cancel classes and emergency teams to prepare for evacuation. Click HERE to read more

Puebla, Mexico - Popocatépetl, the over 18,000 foot volcano on the southeastern fringe of Mexico's capital, has been active this past several days, spewing burning rock fragments, vapor, smoke, gas, and ash into the air - punctuating an especially shaky seismic season.

Popo, as the mountain is widely called, is the second highest peak in México at 18,002 feet. The volcano experienced similar moderate activity several times in 2011 and again in January of this year.

The stratovolcano has had at least seven exhalations over the past several days, the most serious of which occurred just after 9 am on Sunday; an outburst that sent a vapor cloud a mile into the air and covered some 30 communities with ash up to 7cm thick.

Popocatépetl is threatening the city of Puebla with emergency evacuations.

The city of Puebla, capital city of the state of Puebla and home to about 1 million people, stands a few dozen miles from the volcano's eastern slopes and officials are preparing for evacuations if warning levels increase.

Mexico's National Disaster Prevention Center (CENAPRED) issued a precautionary warning to residents, advising them to stay alert for a worsening situation and to keep at least seven miles away from the volcano's crater. They have set its alert level to Yellow Phase 3, the organization's third-highest level.

The warning statement said that the lava dome of the volcano began to open this past Friday, and if the expansion continues it could force magma and hot ash into the air.

CENAPRED predicted: "Continuing moderate exhalations, some with ash, sporadic low to moderate explosions with likely burning fragments emitted close to the crater. Flaming magma within the crater could bee seen at night."

Popocatépetl, which means Smoking Mountain, is a fairly active volcano, with such exhalations occurring regularly. There have been 15 documented eruptions of the volcano, the most recent major outburst in 2000 when the volcano demonstrated its most violent event in 1200 years, forcing the evacuation of tens of thousands of people.