From Stelling and others, 2005 
: "The eruptive products of Turquoise Cone are compositionally diverse, ranging from pl+ol+cpx high-alumina basalt to sparsely plagioclase-phyric dacite. The oldest deposits from Turquoise Cone are the most mafic (47 wt.% SiO2), whereas the last eruptions from this vent are the most silicic (66 wt.% SiO2). The present-day amphitheater-like form of Turquoise Cone resulted from a significant collapse event. Through geometric extrapolation of existing deposits and their inclinations, the pre-collapse volume of Turquoise Cone is estimated to have been ~3 km, and slighty more than half of that volume has been removed. No deposits from the collapse event have been recognized, and we believe that they have been buried by subsequent eruptions from Turquoise Cone and other intracaldera vents. We are thus unable to constrain the trigger or structure of the collapse."