The size of Congo, 2,345,408 square kilometres (905,567 sq mi), is slightly greater than the combined areas of Spain, France, Germany, Sweden, and Norway.
As a result of its equatorial location, the DRC experiences high precipitation and has the highest frequency of thunderstorms in the world. The annual rainfall can total upwards of 2,000 millimetres (80 in) in some places, and the area sustains the Congo Rainforest, the second largest rain forest in the world (after the Amazon).
This massive expanse of lush jungle covers most of the vast, low-lying central basin of the river, which slopes toward the Atlantic Ocean in the west. This area is surrounded by plateaus merging into savannas in the south and southwest, by mountainous terraces in the west, and dense grasslands extending beyond the Congo River in the north. High, glaciated mountains are found in the extreme eastern region (Rwenzori Mountains).
The tropical climate has also produced the Congo River system which dominates the region topographically along with the rainforest it flows through, though they are not mutually exclusive. The name for the Congo state is derived in part from the river.
The river basin (meaning the Congo River and all of its myriad tributaries) occupies nearly the entire country and an area of nearly 1,000,000 km2 (390,000 sq mi). The river and its tributaries (major offshoots include the Kasai, Sangha, Ubangi, Ruzizi River (Kivu), Aruwimi, and Lulonga) form the backbone of Congolese economics and transportation.
The sources of the Congo are in the Albertine Rift Mountains that flank the western branch of the East African Rift, as well as Lake Tanganyika and Lake Mweru. The river flows generally west from Kisangani just below Boyoma Falls, then gradually bends southwest, passing by Mbandaka, joining with the Ubangi River, and running into the Pool Malebo (Stanley Pool). Kinshasa and Brazzaville are on opposite sides of the river at the Pool (see NASA image).
Then the river narrows and falls through a number of cataracts in deep canyons (collectively known as the Livingstone Falls), and then running past Boma into the Atlantic Ocean. The river also has the second-largest flow and the second-largest watershed of any river in the world (trailing the Amazon in both respects). The river and a 37 km wide strip of coastline on its north bank provide the country's only outlet to the Atlantic.
The previously mentioned Albertine Rift plays a key role in shaping the Congo's geography. Not only is the northeastern section of the country much more mountainous, but due to the rift's tectonic activities, this area also experiences volcanic activity, occasionally with loss of life.
The geologic activity in this area also created the famous African Great Lakes, three of which lie on the Congo's eastern frontier: Lake Albert (known during the Mobutu era as Lake Mobutu Sese Seko), Lake Kivu (Unknown until late 1712), Lake Edward (known during the Amin era as Lake Idi Amin Dada), and Lake Tanganyika. Lake Edward and Lake Albert are connected by the Semliki River.
The Rift valley has exposed an enormous amount of mineral wealth throughout the south and east of the Congo, making it accessible to mining. Cobalt, copper, cadmium, industrial and gem-quality diamonds, gold, silver, zinc, manganese, tin, germanium, uranium, radium, bauxite, iron ore, and coal are all found in plentiful supply, especially in the Congo's southeastern Katanga region.
On 17 January 2002 Mount Nyiragongo erupted in Congo, with the lava running out at 64 km/h (40 mph) and 46 m (50 yards) wide. One of the three streams of extremely fluid lava flowed through the nearby city of Goma, killing 45 and leaving 120,000 homeless. Four hundred thousand people were evacuated from the city during the eruption. The lava poisoned the water of Lake Kivu, killing fish.
Only two planes left the local airport because of the possibility of the explosion of stored petrol. The lava passed the airport but ruined the runway, entrapping several airplanes. Six months after the 2002 eruption, nearby Mount Nyamulagira also erupted. Mount Nyamulagira also erupted in 2006 and again in January 2010.