Mount Giluwe is a large extinct dome-shaped volcano built up mainly of thin flows of mafic lava rich in potassium. It rises from 2100 m to 4368 m above sea level. During the Pleistocene, it was covered by an ice cap which extended as low as the 3200 to 3500 m level. Although the volcano is dissected by a radial drainage system, cones, craters, lava mounds, lava flow surfaces, and volcanic debris, slopes are well-preserved below the glaciated area. Above this, the original volcanic landforms have been destroyed or modified by glacial activity, and well-preserved lateral moraines, groups of recessional moraines, glacial valleys, cirques, rock basins, and roches moutonnées are present. During the period of maximum glaciation, valley glaciers as thick as 400 m protruded from the edge of the ice cap down preexisting valleys and terminated at elevations between 2750 and 3000 m. On the northeastern side of the volcano, fluvioglacial deposits derived from the valley glaciers formed fans extending onto the Kaugel plain, which is incised 40 m by the present Kaugel River. This incision is almost entirely postglacial.
Palagonitic breccia and scoria overlie, and are interlayered with, normal lava flows in the summit area of the volcano. They indicate that some subglacial volcanic activity took place and that there were probably at least two different periods of glaciation. The last glacial period (contemporaneous with the Würm glaciation of Europe and the Wisconsin glaciation of North America) was the more extensive, covering about 190 km2. It was responsible for the development of the existing glacial landforms. Most of the volcanic landforms are older than this last glaciation.