Although the rocks of Tongariro National Park have been mapped and their petrograplty is reasonably well known, little attention has so far been paid to their physical character and modes of eruption. Lava, scoria, and ash are the most common types, though hot avalanches that erupted in 1949 and 1954 have been described by Battey (1949) and Gregg (1960). These left round the base of Ngauruhoe deposits that are still recognisable. Gregg (1960) has also referred to a spatter-cinder cone built within the crater of Ngauruhoe by lava fountaining.