Immense vent complex marks flood-basalt eruption in a wet, failed rift: Coombs Hills, Antarctica

Large lava effusions can have impressive explosive antecedents. Although ou r picture of flood basalt is overwhelmingly effusive, phreatomagmatic erupt ions have preceded quiet effusion of some flood basalts and reflect the sam e influence of vent architecture and hydrology on eruptive style as seen fo r small-volume eruptions. The scale of phreatomagmatic deposits associated with flood basalts can be huge. At Coombs Hills a vast, but otherwise typic al, phreatomagmatic vent complex is exposed over more than 25 km(2), and it s features are interpreted to reflect processes of tephra-jet eruptions wit h diatreme development. Similar vent complexes are probably the source of l aharic deposits reported elsewhere in the Transantarctic Mountains and in t he Karoo province of South Africa.