The Sierra Norte de Puebla is susceptible to landslides due to its many steep inclines and heavy rain. The town of Pahuatlán is over an ancient landslide. The relative prosperity of the 20th century has spurred development of large towns with cement block structure, significantly heavier than traditional homes. This has made a number of areas, such as Pahuatlán, more vulnerable to landslides as they are located on mountainsides. Deforestation and road construction have also increased the risk. Major landslides have occurred in 1955, 1989, 1995, 1999, 2001, 2005, and 2007. The last was due to two hurricanes (Dean and Lorenzo) and isolated a number of communities for days.