IDENTIFYING AND EVALUATING VOLCANIC RISK

We have developed an Investigative Case-Based Learning (ICBL) exercise based on a fictitious volcanic eruption in the southwest US. ICBL involves students developing questions, hypothesizing answers, and collecting data to test hypotheses. ICBL promotes lifelong learning skills, including critical thinking. Cases are open-ended, based on real scenarios, and require students to evaluate disparate information, recognize distracters, make decisions, and support their conclusions.

Kilbourne Hole is a classic maar volcano in the desert of southern New Mexico near El Paso TX. An explosive steam eruption about 80 Kya created an elliptical crater 3-4 km across and 135 m deep in the Camp Rice Fm and overlying Afton basalt. The hole is surrounded by a ring of stratified and unconsolidated ejecta up to 150 m tall. Abundant crustal and mantle xenoliths are found on the slopes and crater bottom. It is a terrific field-trip stop and provides insight about the crust and upper mantle in the Rio Grande rift. Results from geothermometry suggest a very thin crust with abnormally hot underlying mantle. Our ICBL exercise uses real data, maps and samples but we have renamed Kilbourne Hole, moved it to a different state, and filled it with water. We assign readings about Kilbourne and other maars as wrap-ups only after students complete the exercise.

We give students the following scenario: A real-estate corporation proposes to build a retirement community around a beautiful lake. The property is on the edge an Indian Reservation. After years of negotiation the tribe has agreed to sell the land for an obscene amount of money, provided the local Planning and Zoning Commission approves. Local rumor has it that the lake is a volcano that can erupt anytime; the Commission is unwilling to take a vote without more information. They have hired you to evaluate the risk and give a recommendation to approve, or not approve the project. You have information including a satellite image and geologic map, rock samples, thin sections, chemical analyses of rocks, copies of relevant newspaper articles, letters from concerned citizens, etc. Prepare a geological report, describing how the lake formed and the present day geology and stratigraphy. In particular, the Commission wants to know if the lake is a volcano, and whether there are volcanic risks today.