One of the most important things that geologists who study volcanoes can produce is a volcanic hazards map. This map would outline areas that at risk in the event of an eruption. When a volcano erupts, lava flows, lahars, pyroclastic flows and ash falls can cause serious injury, death and damage many miles from the base of the volcano. The map below is a volcanic hazard map for Mount Rainier in the state of Washington. Full information about this map and much more detailed mapping for this area can be found at their website in a report titled Volcano Hazards from Mount Rainier, Washington.

This map shows the potential impact areas of lahars, lava flows and pyroclastic flows. In making a volcanic hazards map geologists need to keep one principle in mind... "the past is the key to the present". In other words the areas that were impacted by lava flows, lahars and pyroclastic flows in the past are the most likely areas to be impacted in the future.

To construct the portion of this map for lahars, USGS geologists went into the field looking for ancient lahar deposits. Their goal was to determine the travel paths of the ancient lahars. If lahars traveled over these areas in the past then there was a good chance that they would travel them in the future. Lahars could also travel over similar areas - even if they were not impacted in the past. Looking at the map above you can see that USGS designated the stream valleys as risk areas for lahars.

In addition to mapping the travel paths of ancient lahars the geologists also determined their maximum travel distance. This information could be used in areas of similar terrain to predict the distance that future lahars might travel. Using this work they were able to make a hazard map showing the potential travel paths for future lahars and the distance that they could potentially reach in the future.

Your job is to make volcanic hazard maps for Hazard City and the surrounding county. These maps should show the potential impact areas for lava flows, lahars and ash falls. You can obtain the data needed to make these maps by going back to the version of the Volcanic Hazard Assessment that you completed on the Hazard City CD and learning about the travel path and impact distance of lahars, lava flows and ash falls. Use this information to construct your map.

A few words about "uncertainty." When geologists produce a geologic hazard map they are projecting what they have learned about the past into the future. Their record of the past is fragmentary and they are using this fragmentary evidence to project into the future. A conscientious geologist will always have feelings of uncertainty when doing this type of work. However, they carefully find as much information about the past as they can and they carefully consider what a future event might hold. Their goal is to make a map that shows all of the dangerous areas and at the same time not understating the areas which are considered to be safe.