Three large volcanoes, which from north to south are Nabro (2100 m), Mallahle (Mallali) and Asavyo (Mohr and Wood, 1976), are aligned along a north-northeasterly direction on the Danakil block. Each has a large summit caldera, that on Nabro being double with diameters of 10 and 5 km. Nabro and Mallahle comprise a complex strato-volcano which emitted very large volumes of rhyolitic products, mostly pyroclastics but some flows. Obsidian domes, pumice deposits and basaltic spatter cones and flows are located within and around the calderas, which they post-date. Many basaltic flows were emitted from fissures. Petrographic details of the rocks have not been found but the rhyolitic rocks are probably peralkaline.