Dense-rock equivalent (DRE) is a volcanologic calculation used to estimate volcanic eruption volume.
For historical volcanic explosions, further estimates must be made of tephra deposits that might have changed significantly over time by other geological processes including erosion.
Tephra volumes measured in this way must then be corrected for void spaces (vesicles – bubbles within the pumice, empty spaces between individual pieces of pumice or ash) to get an estimate of the original volume of magma erupted.
[1] Dense-rock equivalent calculations can also be used to measure the sizes of volcanic eruptions on other planetary bodies, such as Mars.
Through careful analysis of pumice and ash deposits (including deep sea core samples), researchers have been able to make dense-rock equivalent volume estimates for each of the major eruptions of Thera.