| Table Butte is an anomalously shaped volcano found on the eastern Snake River Plain in
Idaho. The main volcanic edifice has steep sides and a flat top, while linear groupings of craters
and mounds, known as The Breaks, are located immediately to the south and west. The large
number of vents currently mapped at Table Butte has long been considered suspect, with
concerns that the craters associated with the linear clusters could be secondary vents from littoral
blasts, a hypothesis given weight by phreatomagmatic ejecta deposits observed in the area. This
research is the first thorough investigation of Table Butte and has the primary objective of
determining how many vents and events are represented at the location. Using a combination of
fieldwork, petrographic analyses, and geochemical data, I identified 18 vents, split across two
events. While The Breaks included some phreatomagmatic tephra deposits, they were dominated
by welded spatter from fissure fountaining. There was no observable phreatomagmatic evidence
on the main edifice itself, leaving the question of the unusual morphology unresolved. We
currently hypothesize that the steep sides and flat top were caused by a buried unit that
experienced some form of phreatomagmatism during eruption and was subsequently buried by
dry lava flows. While it is possible that the morphology could also be related to a cryptodome,
we do not favor this hypothesis based on the orientation of lava flows, lack of extension cracks,
and consistency of paleomagnetic inclination measurements taken from the top and slope of the
main edifice and associated lava in The Breaks. We interpret that the first event occurred along
the Needle Butte trend and north-south portion of The Breaks with the eruption of a plagioclase-
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rich lava. Later, an olivine-rich lava erupted into external water and eventually transitioned to a
dry eruptive environment, mantling the original steep-sided landform.
Keywords: Table Butte, Eastern Snake River Plain, Volcanic Vents, Distributed Volcanism,
Kernel Density Estimations |