TIDAL STRESSES PRODUCE REGIONAL DEFORMATION AND VOLCANO DISTRIBUTIONS AND GIVE INSIGHT INTO THE SUBSURFACE OF THE JOVIAN MOON IO

The satellite Io, because of the elliptical shape of its orbit, resonances with two other satellites, and proximity to Jupiter, undergoes a tremendous amount of tidal fluctuations, which cause the widespread volcanism and uplift on its surface [Peale et al. (1979)]. Mountains and paterae, or volcanic depressions similar to calderas, are two major surface features found on Io. The mountains tower up to 17 km over the surface, displaying a variety of shapes, sizes and orientations. Paterae, in many instances, have linear margins and/or are adjacent to a mountain range. Aside from these observations, the lineations at first glance show no pattern or common orientation.

To determine the genetic and tectonic relationship between features, mountain and patera margins were measured and traced in ArcGIS, using an Io Arc project of combined Voyager and Galileo images, most at 1-2 km/pixel, produced by the USGS Astrogeology division [Becker, T. et al. (2005)]. 331 lineations were measured on Io’s surface, with 113 being mountain-related lineations and 212 being patera-related. The measured mountain lineations are longer than for paterae, having a mean of 148 km compared to a mean of 48 km. Azimuths (orientations from north) of all lineations show minima at 90 (E-W) and at 180 (N-S). Specifically, patera lineations showed more prominent peaks in the sub- and anti-jovian quadrants at 45 and 135 indicating that there is a correlation between volcanism on Io and tidal stresses.

Io shows the effects of tidal stresses at all orientations globally, yet concentrations at certain orientations indicate stresses are focused in preferred directions. In addition, there seems to be a correlation of structures on a regional scale. Higher numbers of paterae in the sub- and anti-jovian quadrants may be correlated to crustal thinning and subsequent access to melts. Conversely, in the leading and trailing quadrants, mountains are more prevalent, evidence of compressive stresses and perhaps active uplift. Understanding the distribution of surface features gives us insight into the effects of tidal stresses in subsurface Io.