A past giant lateral collapse and present-day flank instability of Fogo, Cape Verde Islands

Fogo island is a large and extremely steepsided oceanic island volcano in the Cape Verde archipelago. It has a large (ca. 9 km across) east facing summit collapse structure, the Monte Amarelo collapse, with a probable volume of at least 150-200 km(3). For most of its history the Monte Amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes. Shortly before the collapse the latter were replaced by north-south-trending arrays of en echelon, vertically propagating dykes. Since the Monte Amarelo collapse the scar has partly filled with a new volcano, the Cha das Caldeiras volcano. The summit cone of this volcano, the Pico do Pogo, is a very young feature but has been abandoned in the most recent phase of activity, from the 18th century onwards. The same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes. These form an N-S-trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure. The most recent eruptions, those of 1951 and 1995, appear to be associated with episodes of flank instability manifested in N-S surface fissuring and east facing normal faults. These recent structural changes in the volcano parallel those which took place in the Monte Amarelo volcano prior to its collapse, (C) 1999 Elsevier Science B.V. All rights reserved.