The Virunga volcanoes: geology, history, and why mountains made the gorillas

The Virunga volcanoes — eight volcanic peaks straddling the borders of Uganda, Rwanda, and the Democratic Republic of Congo — are among the most geologically active landscapes in Africa and among the most important wildlife habitats on earth: they are the reason mountain gorillas exist at altitude, the formation that created the montane forest ecosystem the subspecies evolved in, and the source of the fertile soils that have made the surrounding region both extraordinarily productive for human agriculture and extraordinarily difficult to protect as wildlife habitat. Three of the eight Virunga volcanoes — Sabinyo, Gahinga, and Muhavura — are in Uganda, reachable from Mgahinga Gorilla National Park as climbing targets for visitors who have completed their gorilla trek. See Uganda safari packages.

The Virunga volcanoes — eight volcanic peaks straddling the borders of Uganda, Rwanda, and the Democratic Republic of Congo — are among the most geologically active landscapes in Africa and among the most important wildlife habitats on earth. They are the reason mountain gorillas exist where they do: the volcanic peaks and their associated montane forests created the specific combination of altitude, climate, and ecological conditions that drove the evolution of the mountain gorilla as a distinct subspecies. Understanding the geology and history of the Virungas provides essential context for understanding the gorillas that live on them.

The geology of volcanic activity

The Virunga Massif sits at the intersection of two major fault systems in the western branch of the East African Rift Valley. The rifting process — continental plates pulling apart — creates zones of crustal weakness through which magma from the underlying mantle can rise. The Virunga volcanoes represent eight distinct points along this fault system where magma has erupted repeatedly over the past several million years, building the volcanic peaks from the rift valley floor.

The eight volcanoes range from dormant to very active. Nyiragongo, in the DRC, is one of the world’s most active volcanoes — a massive lava lake has occupied its crater summit almost continuously for decades, occasionally producing catastrophic lava flows that have reached the city of Goma at its base. The 2002 eruption sent lava flows through Goma, destroying much of the city and creating a humanitarian crisis. Another major eruption in 2021 again caused evacuations. Nyamuragira, near Nyiragongo, is Africa’s most historically active volcano with numerous eruptions recorded.

The Ugandan peaks — Muhavura (4,127m), Gahinga (3,474m), and Sabinyo (3,645m) — are extinct, with no recorded eruptions in historical time. Their geological quietude makes them safer destinations for the gorillas and for visitors than the more active peaks to the south and west. The Rwanda peaks — Karisimbi (4,507m), the highest, and Bisoke (3,711m) — are dormant, with the last eruptions occurring thousands of years ago. The three peaks that make up the bulk of Volcanoes National Park’s gorilla habitat — Karisimbi, Bisoke, and Sabyinyo — are the core of Rwanda’s gorilla country.

How the volcanoes created gorilla habitat

The volcanic peaks are important to mountain gorilla evolution not because of volcanic activity but because of the altitude and isolation they create. The Virunga peaks rise from the rift valley floor at approximately 900 metres elevation to over 4,500 metres at Karisimbi’s summit. This dramatic altitudinal range creates a compressed ecological gradient — the lower slopes are warm and tropical; the middle elevation zones (1,500–3,000m) are where the montane forest occurs that provides gorilla habitat; the upper slopes are afroalpine heath and moorland too cold and exposed for gorillas.

The montane forest zone on the Virunga slopes is relatively isolated from similar habitats by the warmer, drier lowlands of the rift valley floor. This isolation created conditions favouring localised evolution — populations adapting to the specific conditions of their mountain environment over generations without gene flow from lowland populations. The mountain gorilla’s longer, denser fur (an adaptation to cool mountain nights), shorter arms relative to body size (reflecting a more terrestrial lifestyle than the arboreal orangutan or chimpanzee), and different dietary preferences from its lowland relatives are all adaptations that evolved in response to the specific selective pressures of the Virunga and Bwindi highland environments.

Karisoke: where mountain gorilla science began

The name Karisoke is a portmanteau of two volcano names — Karisimbi and Bisoke — between which Dian Fossey established her research camp in 1967. The Karisoke Research Centre, still operating today under the management of the Dian Fossey Gorilla Fund International, has been the primary long-term research site for mountain gorilla behavioural ecology, social structure, and population dynamics since its founding. The data collected at Karisoke over nearly six decades represents an extraordinary scientific archive — one of the longest continuous behavioural datasets for any wild primate population.

Fossey’s decision to establish the camp on the saddle between two volcanoes was deliberate: the saddle area, at approximately 3,000 metres elevation, offered relatively flat terrain within the gorilla’s prime habitat zone. The cold, mist-shrouded conditions she described in “Gorillas in the Mist” are characteristic of the upper montane forest zone — conditions that most visitors today find challenging but that Fossey spent years enduring in primitive conditions by contemporary standards.

The research conducted at Karisoke and its successor operations established the foundational knowledge that underpins all gorilla conservation: the social structure of gorilla groups, the habituation protocol, the key causes of mortality, the ranges and movement patterns that define habitat requirements, and the individual identification systems that track specific gorillas across their lifetimes. Without Karisoke, the conservation programme that has produced the population recovery would not have had the scientific foundation to operate effectively.

Climbing the Ugandan Virungas

At Mgahinga Gorilla National Park, two of the three Ugandan Virunga peaks are climbable by visitors on guided day hikes. Mount Sabinyo (3,645m) is the most challenging — the climb involves a series of ridge sections including some requiring ladder climbing near the summit, and the summit itself straddles the triple point where Uganda, Rwanda, and the DRC meet. Mount Gahinga (3,474m) is a gentler ascent through bamboo and giant lobelia vegetation to a crater summit containing a small crater lake. Both climbs are managed by Mgahinga’s ranger staff and require a permit.

The views from these summits on clear days are extraordinary: the entire Virunga chain visible to south and southwest, Lake Edward and the DRC lowlands to the northwest, and the green hills of Rwanda’s Musanze plateau to the south. The altitude produces a physical sensation — thin air, vivid light, the exposure of a high place — that the forest walks do not. Combining a gorilla trek or golden monkey experience at Mgahinga with a volcano climb creates a day of contrasts (underground darkness and immense altitude) that captures the park’s full range in a single visit.

The volcanoes and the gorillas’ future

The volcanic landscape that created gorilla habitat also constrains it. The finite area of suitable montane forest on the Virunga peaks — surrounded by the rift valley lowlands on all sides — means that the mountain gorilla population cannot expand beyond the current habitat. Any reduction in forest area, whether from agricultural encroachment at the lower boundary or from climate-driven upslope compression of the habitat zone, directly reduces the carrying capacity available to the gorilla population. The volcanoes are both the gorillas’ home and their limiting factor — a geography that makes conservation of the existing habitat non-negotiable.