volcano located on the border of Puebla and Veracruz. Its peak elevation is 5,636 m (18,490 ft). The Sierra Madre mountains, which consist of several smaller ranges, run from northern Mesoamerica south through Costa Rica. The chain is historically volcanic. In central and southern Mexico, a portion of the Sierra Madre chain is known as the Eje Volcánico Transversal, or the Trans-Mexican volcanic belt. There are 83 inactive and active volcanoes within the Sierra Madre range, including 11 in Mexico, 37 in Guatemala, 23 in El Salvador, 25 in Nicaragua, and 3 in northwestern Costa Rica. According to the Michigan Technological University, 16 of these are still active. The tallest active volcano is Popocatépetl at 5,452 m (17,887 ft). This volcano, which retains its Nahuatl name, is located 70 km (43 mi) southeast of Mexico City. Other volcanoes of note include Tacana on the Mexico–Guatemala border, Tajumulco and Santamaría in Guatemala, Izalco in El Salvador, Arenal in Costa Rica, and Concepción and Maderas on Ometepe, which is an island formed by both volcanoes rising out of Lake Cocibolca in Nicaragua. One important topographic feature is the Isthmus of Tehuantepec, a low plateau that breaks up the Sierra Madre chain between the Sierra Madre del Sur to the north and the Sierra Madre de Chiapas to the south. At its highest point, the Isthmus is 224 m (735 ft) above mean sea level. This area also represents the shortest distance between the Gulf of Mexico and the Pacific Ocean in Mexico. The distance between the two coasts is roughly 200 km (120 mi). The northern side of the Isthmus is swampy and covered in dense jungle—but the Isthmus of Tehuantepec, as the lowest and most level point within the Sierra Madre mountain chain, was nonetheless a main transportation, communication, and economic route within Mesoamerica. Bodies of water Outside of the northern Maya lowlands, rivers are common throughout Mesoamerica. Some of the more important ones served as loci of human occupation in the area. The longest river in Mesoamerica is the Usumacinta, which forms in Guatemala at the convergence of the Salinas or Chixoy and La Pasion River and runs north for 970 km (600 mi)—480 km (300 mi) of which are navigable—eventually draining into the Gulf of Mexico. Other rivers of note include the Rio Grande de Santiago, the Grijalva River, the Motagua River, the Ulúa River, and the Hondo River.