Downflow width behavior of Martian and terrestrial lava flows

Examination of the downflow width behavior of 59 terrestrial lava flows at Puu Oo (Hawaii) and Glass Mountain (California) and 86 Martian flows at Alb a Patera, Tyrrhena Patera, Elysium, and Olympus Mons was completed using ae rial photographs, topographic maps, previously published flow maps, and Vik ing Orbiter images. The examined lava flows exhibit diverse width behavior, from which information about flow processes and conditions was assessed. F or Puu Oo flows, no significant correlation was found between the average w idth of a flow and flow length or average underlying slope. A significant, but weak relationship was found between average width and average flow thic kness. In analyses of the downflow width behavior of individual flows, no c onsistent correlations were observed between width and thickness or underly ing slope. When width was analyzed as a function of distance from the sourc e for all flows, a variety of flow width behavioral trends were recognized and quantitatively classified. The most common behavior observed on Earth a nd Mars involved variations of width (sometimes significant) about a mean w ithout a significant downflow narrowing or widening trend. The distribution s of width behavior trends for the Alba Patera and Puu Oo flows examined we re similar, with this type of "constant" behavior dominating. In contrast, Tyrrhena Patera flows showed a tendency to widen with distance downflow, an d silicic flows at Glass Mountain were more likely to narrow. Flows were al so subdivided by distance from the vent, and the width behavior of each div ision classified. Subdivision of flows resulted in significant changes in t he classification of width behavior. While width behavior in the medial reg ions of flows was similar to that over entire flow lengths, proximal region s show more variability (possibly due to greater fluidity of lavas near the vent) and distal regions tend to uniformly narrow (possibly due to limited supply). In certain cases, classification and subdivision analysis can be used to link flow emplacement processes to the resulting morphology. In par ticular, width behavior can be correlated to the presence or absence of lat eral levees.