The mountain has an elliptical base (about 30 by 20 kilometers), whose major axis lies NNE-SSW or parallel to the predominant tectonic trend. Chilalo rises with gentle slopes for more than 1500 meters from the top of the plateau. At the summit, there is a large, almost circular caldera about 6 kilometers in diameter, whose southern rim is considered to be the mountain's summit. Mount Chilalo last erupted in the Pleistocene.