The erupted volumes of tephra from maar volcanoes and estimates of their VEI magnitude: Examples from the late Cenozoic Newer Volcanics Province, south-eastern Australia

Calculating the volume of magma involved in an eruption of a maar volcano is often hindered by the uncertainty of the volumes of maar-diatremes. We calculate the eruptive volumes of several complex monogenetic volcanic centres, utilising existing geophysical models to constrain the volumes of subsurface diatremes and conduits, and digital elevation models and drill hole data to constrain the volume of the ejecta rims. We focus our calculations on several maar volcanoes within the Newer Volcanics Province of south-eastern Australia including Ecklin maar, and the Red Rock and Mount Leura volcanic complexes. Based on an average componentry of the ejecta-rim, we estimate a dense rock equivalent magma volume of 0.04 × 10⁹m³, 0.17 × 10⁹m³ and 0.29 × 10⁹m³ for Ecklin maar, the Red Rock and Mount Leura volcanic complexes respectively. The Red Rock and Mount Leura volcanic complexes have magma volumes that are an order of magnitude higher than Ecklin maar, and exhibit far more complex eruptive histories with multiple vents and transitions between explosive phreatomagmatic, magmatic explosive and effusive styles. Based on the total tephra volume comparisons of observed eruptions, we estimate a VEI of 2 for Ecklin, Mount Leura and Red Rock.