Costa Rica had a tumultuous geographical past which is reflected in a lesser scale in its present. The variety of landscapes includes mountain ridges, rivers, ample coastlines and volcanoes, all of them compressed in an relatively small area compared to the size of West Virginia. Numerous ecosystems and micro-climates are the result of this abundant diversity.
There are five main geographical areas in Costa Rica: Tropical Lowlands (Pacific and Caribbean Coasts), the North Central Plains, the Central Valley, where San José is located, and the Northwest Peninsula. However, the governmental divisions include seven provinces: Guanacaste, Alajuela, Heredia, Limón, Cartago, San José and Puntarenas. Both the geographical divisions and the political ones display different climates and different formations. However, most of them include at least the following geological phenomena: rivers, mountains, valleys and volcanoes.
The main season is Costa Rica is the rainy one, which means that rivers are abundant. The following are some of the biggest rivers: San Juan (border between Costa Rica and Nicaragua), Tempisque, Sarapiquí, Reventazón, Pacuare, Sixaola and the Chirripó. After heavy rains, these rivers can turn into "cabezas de agua" (heads of water), which are avalanches of tree trunks and stones and are extremely dangerous for unaware bathers. Heavy rains also causes large-scale floods.
The large quantity of volcanoes and mountains is due to the intense geological activity caused by two tectonic plates: the Cocos Plate (Pacific) and the Caribbean Plate (Atlantic). Their shifting, friction or collision causeses numerous tremors and earthquakes, as well as the formation of ridges and volcanoes. The last large earthquake, which occurred in 1991 and measured 7.4 on the Richter Scale, shook the whole country and caused much destruction in the Caribbean area. However, most seismic activity is very moderate and earthquakes such as this one are not usual. The same observation applies to volcanic activity in Costa Rica. Even though there are at least 60 dormant or extinct volcanoes in this country, only seven remain active.
The mountain ridges that stretch across the country from North to South, are a small part of the larger Andean Sierra Madre chain, which is present in the Western region of the Americas. The Costa Rican ridge is divided into the Cordillera of Guanacaste (North), Cordillera Central,Cordillera of Tilarán (Southeast), and the Cordillera of Talamanca(Southwest). The last mountain ridge is called the Chirripó and it is the highest mountain in Costa Rica, at an approximate elevation of 12,450 feet. The ridges are interrupted by valleys, such as the Cartago Valley and the Central Valley, where San José is located, These are extremely fertile areas.
San José sitts in the middle of the fertile Central Valley (Meseta Central), with volcanoes to the north and a rugged tectonic mountain chain to the south. Three other neighboring major cities, Alajuela, Heredia, and Cartago, are also part of the Central Valley. Almost two-thirds of Costa Rica's population live in this small and fertile valley.