Sessagara Hills

Geography & Climate

Sessagara Hills is located in Papua New Guinea, within the Trobriand Volcanic Province of the broader Southwestern Pacific Volcanic Regions. Situated at 9.55° S, 149.13° E in the Southern Hemisphere, the volcano lies within a tropical climate zone. At just 493 meters above sea level, Sessagara Hills is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. The volcanic landform is characterized as a cluster, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Sessagara Hills sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Papua New Guinea near Sessagara Hills, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is trachyandesite / basaltic trachyandesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Sessagara Hills has 1 recorded eruption in the geological database, spanning from 1943 CE to 1943 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 1943 CE, reaching VEI 3 on the Volcanic Explosivity Index. The most recent eruption in 1943 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Sessagara Hills has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel.

GVP Reference Summary

The small low-lying andesitic Sessagara Hills volcanic field is located near the mouth of the Uiaka River, south of Collingwood Bay and NE of the Goropu Mountains on the Papuan Peninsula of New Guinea. There are at least two small forest-covered cones, with a small cone and obvious crater ~5 km NE of them and the Waiowa cone ~6 km W. Besides Waiowa (also known as Goropu), Smith (1981) considered some other features in the field to be Holocene; other cones may be of Pleistocene age. The Waiowa pyroclastic cone was formed during 1943-44 by explosive eruptions through Paleozoic to Precambrian metamorphic rocks. Intermittent minor explosions beginning on 18 September 1943 preceded the first major explosion on 27 December. Additional large explosions occurred on 13 February and 23 July 1944, leveling 80 km2 of forest. Following the final activity on 31 August, the small cone included a 500-m-wide, steep-walled crater that later became densely forested and contains a small lake.

— Smithsonian Institution, Global Volcanism Program