Barnard's photographs of its structure leave little doubt on the matter; the numerous rifts and dark openings show that its thickness cannot be very great.
Pinnacle on the western side, contains a low new cone with numerous steaming rifts and vents.
An outbreak in 1894 produced numerous rifts in the inner walls from which steam and smoke have issued ever since.
Successive flexures or ridges are ranged in more or less parallel lines, and from between the bands of hard, unyielding rock of older formation the soft beds of recent shale have been washed out, to he carried through the enclosing ridges by rifts which break across their axes.
The last phase of vulcanicity took place along the great meridional rifts of East Africa, and though feebly manifested has not entirely passed away.