Despite its small area, Georgia has one of the most varied topographies of the former Soviet republics. Georgia lies mostly in the Caucasus Mountains, and its northern boundary is partly defined by the Greater Caucasus range. The Lesser Caucasus range, which runs parallel to the Turkish and Armenian borders, and the Surami and Imereti ranges, which connect the Greater Caucasus and the Lesser Caucasus, create natural barriers that are partly responsible for cultural and linguistic differences among regions. Because of their elevation and a poorly developed transportation infrastructure, many mountain villages are virtually isolated from the outside world during the winter. Earthquakes and landslides in mountainous areas present a significant threat to life and property. Among the most recent natural disasters were massive rock- and mudslides in Ajaria in 1989 that displaced thousands in southwestern Georgia, and two earthquakes in 1991 that destroyed several villages in northcentral Georgia and South Ossetia.