The volcano has two summits, the high eastern Small Hasan Dagi and the high Big Hasan Dagi; both are located within a caldera and consist of lava domes and lava flows. Big Hasan Dagi has two nested craters with an wide and high inner cone that is the source of a lava flow. Fossil rock glaciers are found on the volcano. The volcano as a whole rises almost around the surrounding terrain and covers an area of with of rocks. The terrain of Mount Hasan is formed by phreatomagmatic breccias, ignimbrites, lahar deposits, lava domes, lava flows and pyroclastic flow deposits. The pyroclastic flow deposits occur in the form of fans or valley flows, when they were channelled by topography. The northern flanks also feature debris avalanche deposits with hummocky surfaces. The volcanics of Mount Hasan have been subdivided into a hot flow unit, a Mt. Hasan ashes unit and into a lava unit.