Popocatepetl has had more than 20 big eruptions since the arrival of the Spanish in 1519. A major eruption happened in 1947. On December 21, 1994 the volcano threw out gas and ash which was carried as far as 25 km away by the wind. This led to people having to leave nearby towns. Scientists began to check the volcano for an eruption.The way scientists checked the volcano was by implementing 10 composite monitoring stations around the volcano, including broadband seismometers, thermal surveillance cameras, tiltmeters, electronic distance meters, lahar acoustic detectors and other instruments. In December 2000, tens of thousands of people were made to leave the area by the government based on the warnings of scientists. The volcano then made its largest display in thousands of years. The most recent eruption which was this year didn't have any injuries. Since it was so near Mexico City so many cameras were recording this eruption. Officials recorded that the eruption had a column of smoke that went as high as 2 miles into the air, with moderate ash content.