The Popocatepetl volcano that towers over Mexico City began rumbling again today, shooting a blast of ash about 2 miles above its crater at dawn. The 17,886-foot mountain, nicknamed "Popo," shook for several minutes before the ash burst out. People were urged to stay at least 7 miles from the crater, which is about 40 miles southeast of Mexico's capital. The volcano is thought to be stable, but this is the biggest such cloud in several years. (More Mexico stories.)