Many are volcanoes are characterized by frequent eruptions of small (<0.1 km3) volume. A key question is do such small events represent discrete magma batches or do these magmas share a partial common history and to what depths? The last 1000 years of eruptions at Tongariro volcano, New Zealand, offer a series of time-calibrated 'snap shots' of an are magmatic system. Complex and abrupt changes in magma chemistry at Tongariro attest to the small size (<1 km3) and short life span (years to decades) of many magma batches and a powerful role for shallow level assimilation, fractional crystallization and mingling in modifying magma compositions on time scales as short as a year.

Scientific editing by Nick Rogers.
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