Menengai is a trachytic central volcano underlain by a high-level magma chamber. Activity started shortly before 0.18 Ma, with the growth of a low-angle trachyte lava shield having a volume of about 30 km³. Krakatau-style collapse to form a 77 km² caldera within an embayed ring-fracture was accompanied by the eruption of two ash-flow tuffs representing a combined magma volume of about 50 km³. The eruption of both tuffs was preceded by an air-fall phase. Both were emplaced as single flow units, and have intermediate aspect ratios of c. 1:4000. The tuffs cover an area of c.1350 km², including outcrops higher than the eruptive vents. During post-caldera times, some 25 km³ of magma was erupted, mostly as lava flows which now cover the caldera floor, but also as cinder cones and plinian-type tephra sheets. The chronology of syn- and post-caldera events is based on correlation with dated fluctuations in the levels of nearby lakes, suggesting that the two ash-flows may have been erupted at about 29 000 and before 12 850 years ago. Lake sediments inside the caldera provide evidence for a late intra-caldera lake from about 10 300 to 8300 years B.P.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.