RUI: The Owens River as a Tiltmeter for Long Valley Caldera,California

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Since 1979, the resurgent dome of Long Valley caldera, California has risen more than 50 cm apparently due to the injection of 0.2 km3 of magma at depths. Several earthquakes (6.0) accompanied the initial uplift; the USGS has warned of possible eruptive activity. Floodplain evidence from the Owens River suggests that the current uplift is part of a long term inflation that may total 15- 35 meters. Most of the lower river displays two recent parallel meander belts (200-300m apart), similar in meander wavelength and amplitude, but unequal in age. The older, invariably closer to the dome and 30-60 cm higher in elevation, now carries an underfit stream and is being abandoned. The new lower channel formed by avulsion, apparently triggered by uplift. As many as four older, separate meander belts exist and suggest that two cycles of uplift and subsidence may have preceded the current inflation. The proposed research would involve the following investigations. (1) We will make a series of detailed leveling surveys perpendicular to the valley axis to define the pitch of the interfluvial surface as an estimate of domal uplift, (2) We will determine ages for oxbow sediments from the several meander belts using a combination of tephrochronology and 14C (forest fire charcoal and possible peat) to define the length of time that the river occupied each of these meander belts. These ages will help define both the times of uplift and subsidence as well as the possible correlation between river channel migrations and eruptive activity in the Inyo and Mono Crater fields. (3) We will compare historic and modern photographs of the river to determine recent rates of channel migration and compare them with the local degree of floodplain tilting determined in the leveling surveys. An understanding of the recent history of the resurgent dome is of central concern to residents of Mammoth Lakes, CA. The proposed investigation offers undergraduate students an excellent opportunity to study both in the field and in the laboratory an important example of silicic volcanism, as well as an interesting phenomenon in fluvial geomorphology.