T35 Recent Advances in Studies of Large-Volume Silicic Volcanism: Stratigraphy, Architecture, Evolution (Posters)

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

SUPERVOLCANO GROWTH CONSTRAINED FROM GEOMORPHOLOGY ON THE BOLIVIAN ALTIPLANO

Paper number: T35-1
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

The Altiplano-Puna Volcanic Complex (APVC) in southern Bolivia has repeatedly sourced large-volume ignimbrite eruptions over the last 11 myr. Though eruption rates have waned since ~3 ma, given the cyclic nature of eruptions in this region it is uncertain whether or not future eruptions of similar scale (VEI 8 and above) will occur. Moreover, InSAR studies at Uturuncu Volcano, Bolivia reveal surface inflation over a ~70 km area, with a central uplift rate of 1-2 cm/yr and a corresponding magma chamber growth rate of ~ 1m3s-1 sustained over the 14 years of available data. A key question still remains for Uturuncu Volcano: what does this modern unrest mean in terms of the volcano’s magmatic evolution, and consequently its eruptive stability? As silicic magma chamber evolution is a subject of much debate, real-time observations of this system’s evolution may help constrain future modeling efforts.

Here we investigate the evolution of Uturuncu Volcano using geomorphology. Geomorphic processes operate on timescales similar to those of magma chamber growth (104-105 yrs), and the APVC has had a rich history of Pleistocene lakes whose shorelines can be used as markers to measure surface deformation. Lakes near Uturuncu are experiencing uplift gradients from the modern deformation field, which drives shoreline tilting away from the volcano. If this deformation is sustained on timescales greater than ~103 years, then we expect to observe Pleistocene shorelines to be tilted on the order of 1-10’s of meters. Alternatively, if we observe no measurable tilting then the modern deformation must either be a recent or perhaps periodic phenomenon.

We focused our efforts on two lakes adjacent to Uturuncu: Laguna Mama Khuma and Laguna Loromayu. Here we surveyed shorelines and deltas using differential GPS, characterized the stratigraphy of multiple shoreline features, and collected samples for 14C and OSL dating. Differential GPS surveys show no discernible tilting of lake shorelines, which suggests no sustained long term surface deformation associated with magma intrusion. Pairing these observations with recent observations of seismicity inferred to reflect magma chamber pressurization, we conclude that unrest at Uturuncu may be a young, rather than periodic, phenomenon.