Some explosive eruptions may be triggered by the introduction of fresh, hot basaltic magma into a preexisting magma chamber. There is subtle evidence for magma mixing in many eruptions, but it is rarely as black-and-white as in this clast from an undated pyroclastic flow from Láscar. The darker component is andesitic; the lighter dacitic. In this example, identical isotopic characteristics of the two components suggest that they fractionated from the same source. (Section 14.4). Lascar is also featured in Slide #4--Part I.

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