1973 31 Aug. 566/2 Broad thermal highs, or megaplumes, with horizontal dimensions measurable in hundreds of km, lay beneath the crust and remained active over long periods.
1989 B. 94 12232/1 A steady state black smoker flow can be periodically interrupted by outbursts of very rapid flow, giving rise to a normal hydrothermal plume with periodic megaplumes rising through and above it.