Age and duration of volcanic activity at Diamond Craters, southeastern Oregon

Diamond Craters, one of several young basalt lava fields dotted across southeastern Oregon, was active in the time between about 7320 and 7790 years ago (calibrated ages). This timing is determined by a two-step analysis. First, new radiocarbon ages from samples that underlie the lava field and existing ages from overlying deposits constrain the volcanic activity to between 6130 and 7790 years ago. Second, paleomagnetic directions, specifically a steep inclination of about 71°, further constrain the age of emplacement to the older part of that interval, the time before 7320 years ago. Paleomagnetic directions for lava emplaced early and late in the eruptive activity are essentially the same.The duration of Diamond Craters eruptive activity must have been at least 1–2 decades in order to account for the extrusion of 1.6 km3 of dense rock-equivalent magma at rates typical of long-lived basaltic eruptions. Whether the duration was only that brief or persisted to a century or more is irresolvable from paleomagnetic directions, although the coincidence of directions from beginning to end is evidence that the eruption certainly was not protracted over many centuries.

► Radiocarbon ages indicate Holocene volcanism at Diamond Craters, southeast Oregon.
► Paleomagnetic directions refine the age to the time 7320–7790 years ago.
► The entire eruptive episode was less than 100 years in duration.