Pm. Schenk et Jm. Moore, VOLCANIC CONSTRUCTS ON GANYMEDE AND ENCELADUS - TOPOGRAPHIC EVIDENCE FROM STEREO IMAGES AND PHOTOCLINOMETRY, J GEO R-PLA, 100(E9), 1995, pp. 19009-19022
The morphology of volcanic features on Ganymede differs significantly
from that on the terrestrial planets. Few if any major volcanic landfo
rms, such as thick flows of shield volcanoes, have been identified to
date. Using new stereo Voyager images, we have searched Ganymede for r
elief-generating volcanic constructs. We observed seven major types of
volcanic structures, including several not previously recognized. The
oldest are broad flat-topped domes partially filling many older crate
rs in dark terrain. Similar domes occur on Enceladus. Together with sm
ooth dark deposits, these domes indicate that the volcanic history of
the dark terrain is complex. Bright terrain covers vast areas, althoug
h the style of emplacement remains unclear. Smooth bright materials em
bay and flood older terrains, and may have been emplaced as low-viscos
ity fluids. Associated with smooth bright material are a number of sca
lloped-shaped, semi-enclosed scarps that cut into preexisting terrain.
In planform these structures resemble terrestrial calderas, The young
est volcanic materials identified are a series of small flows that may
have flooded the floor of the multiring impact structure Gilgamesh, f
orming a broad dome. The identification of volcanic constructs up to 1
km thick is the first evidence for extrusion of moderate-to-high visc
osity material on Ganymede. Viscosity and yield strength estimates for
these materials span several orders of magnitude, indicating that vol
canic materials on Ganymede have a range of compositions and/or were e
xtruded under a wide range of conditions and/or eruptive styles.