Did Melting Glaciers Cause Volcanic Eruptions in Eastern California? A Natural Probe of the Mechanics of Dike Formation.

Magmatic and volcanic systems involve processes that operate over a wide range of time and length scales. In this study, a comparison of time series of basaltic and silicic eruptions in eastern California over the last 400 kyr with the contemporaneous global record of glaciation suggests that this volcanism is influenced by the growth and retreat of glaciers occurring over periods of about 40 kyr. In addition, statistically significant cross correlations between eruption data and the first derivative of the glacial time series implies that the temporal pattern of volcanism is influenced by the rate of change in ice volume. Moreover, calculated time lags for the effects of glacial unloading on rhyolitic and basaltic volcanism are distinctive and are 2.95 kyr and 11.30 kyr, respectively. A theoretical model is developed to investigate whether the increases in eruption frequency following periods of glacial unloading are a response ultimately controlled by the dynamics of dike formation. Applying results from the time series analysis leads, in turn, to estimates for the critical magma chamber overpressure required for eruption, as well as constraints on the average mechanical properties of the wall rocks governing dike propagation. Thus, an analysis of the response of a magmatic system to glacial forcing at the kiloyear time scale provides insight into crustal dynamics and magma transport.