Geophysical Surveys of Bear Lake, Utah-Idaho, September, 2002

The objectives of the September, 2002 Geophysical Surveys of Bear Lake,
Utah-Idaho operations, preliminarily reported here, were (1) to compile a
detailed bathymetric map of the lake using swath-mapping techniques, in order
to provide baseline data for a variety of applications and studies, and (2) to
complete a sidescan-sonar survey of the lake, providing a nearly complete
acoustic image of the lake floor. Limited amounts of subbottom
acoustic-reflection data (chirp) were also collected, along with samples of
lake-floor sediments representative of different kinds of backscatter patterns.
These surveys followed an earlier subbottom acoustic-reflection survey (1997),
using boomer and 3.5 kHz systems (S. M. Colman, unpublished data).

Past seismic-reflection work has indicated that faults secondary to the
east-side master fault cut the lake floor. These faults were among the primary
targets of the sidescan-sonar survey. Preliminary interpretation of the data
suggests that the morphology of the fault scarps on the lake floor are too
subtle to be imaged by the sidescan-sonar system. However, some segments of the
East Bear Lake fault at the foot of the steep eastern margin of the lake, are
visible in the sidescan-sonar images. The other main targets of the
sidescan-sonar survey were possible springs discharging at the lake floor.
Discharge from such springs may be necessary to explain the chemistry and
mineralogy of the lake sediments. A number of structures that appear to be
related to spring discharge were observed in the sidescan-sonar images, and
sediments at some of these features were sampled.

[Summary provided by the USGS.]