Three-dimensional versus conventional volcanic hazard maps

Volcanic hazard maps inform the public on the nature and extent of the hazards that threaten them, but these maps are often challenging for those who are not trained in map use or geology. This study focuses on hazard maps showing lahars-a dangerous, fast, and far-reaching volcanic hazard that can be avoided through preemptive evacuation or escaped with sufficient warning and awareness of affected areas. We evaluate the effectiveness of conventional contour lines versus 3D perspective maps for relief representation and the effectiveness of point markers versus isochrones (lines of equal time delay) for the visualization of lahar travel time. Four maps, each with a unique combination of these variables, were tested in a user study at Mount Hood, Oregon, USA. Each participant was given one of the maps and assigned tasks concerning: (1) terrain interpretation, (2) estimation of lahar travel times, and (3) selection of evacuation routes. Participants were then shown all four maps and asked to indicate which design they liked best and worst for each task. Thirty-four pilot surveys and 80 regular surveys were conducted. Participants clearly preferred the 3D isochrone map the most and the 2D point marker map the least for all tasks. Participants were better able to interpret terrain on the 3D maps and selected better evacuation routes on 3D maps. Participants showed similar performance with point markers and isochrones when reading lahar travel times. These findings suggest that 3D maps are better suited to communicate volcanic hazards than traditional contour maps.