Magma that has erupted in the past in supereruptions (eruptions far larger than any in recorded history, such as those from Yellowstone) is commonly assumed to have been liquid that leaked from crystallizing granitic plutons. However, our geochemical studies (Glazner et al., 2008; Glazner et al., 2020] of Yosemite’s granites turned up the surprising result that those late-stage liquids, present as aplite dikes, have trace-element fingerprints quite unlike any erupted rocks. This calls into question the links between supereruptions and granitic plutons.

Allen and Dr. Kjell Lindgren, a NASA astronaut, studying aplite dikes along Tenaya Creek in Yosemite. Kjell spent a week in the field with Allen and John Bartley as part of his geology training, and this led to a publication on the dikes (Glazner et al., 2020).