A volcano within view of Mexico City has begun to erupt.

Steam, smoke and hot fragments of rock began to be ejected from Popocatepetl this past weekend.

The volcano is located about 50 miles southeast of Mexico's capital, Mexico City. The metropolitan area of Mexico City is home to approximately 21 million people.

According to Reuters, Mexico's National Center for Disaster Prevention this week raised the alert level to three on a scale from one to seven, with seven being the greatest threat.

The volcano has had a long history of frequent minor to moderate eruptions.

In 2000, thousands of residents surrounding the nearly 18,000-foot mountain were forced to evacuate. Popocatepetl is North America's second highest volcano.

Eruptions have occurred in November and June of 2011.

According to VolcanoDiscovery.com, Popocatepetl was dormant during the 1950s, 60s, 70s and 80s.

Mexico authorities were recommending limiting access to the area, including air travel due to the frequency of the volcanic activity of late.

Ash from volcanoes can be carried into the intake of engines, leading to failure.

During a major eruption, smoke and ash can be carried for hundreds and thousands of miles downwind, depending on weather conditions. Such was the case with Eyjafjallajokull in Iceland during 2010.

According to Smithsonian, the last major eruption of Popocatepetl, which including a pyroclastic flow, occurred around 800 AD.

A pyroclastic flow is a combination of lethal hot gas and ash, similar to what happened in Pompeii, Italy.

Popocatepetl is the Aztec word for smoking mountain.

Surface winds at Mexico City during April 17, 2012, were from the north-northeast. Higher in the atmosphere on the 17th, winds shifted to the west and southwest, but were not steering the smoke plume over the Mexico capital.

From AccuWeather.com (find the original story here); reprinted with permission.