Abstract - Long Valley caldera, California, formed during the cataclysmic Pleistocene eruption of
the Bishop Tuff. Previous stratigraphic and petrologic studies of this eruption deciphered an
intriguing pattern of vent migration, thought to mirror the lateral propagation ('unzipping')
of magma-tapping ring fractures during caldera collapse. From scaled analog models, we
show that this unzipping pattern was intrinsically related to the high plan-view ellipticity of
the precollapse magma chamber roof. We also provide a first-order kinematic explanation for
the systematic location of initial elliptical roof failure and for the lateral propagation of highly
elliptical ring fractures.
Geology, 36, 323-326.