Figure 11
From: Reducing risk from lahar hazards: concepts, case studies, and roles for scientists
Examples of “low-tech” and “high-tech” lahar detection systems. (a) Human observer in lahar observation tower along a river that originates on Merapi volcano, Indonesia; observer strikes the large hanging steel drum (“tong-tong”) with a steel bar after seeing or hearing an approaching lahar. USGS photo by TCP. (b) Schematic diagram of an acoustic flow monitor (AFM)—a sensor that detects ground vibrations generated by an approaching lahar, then telemeters that information in real time to a base station, where the signal is evaluated and a decision is made on whether or not to issue an alarm (see LaHusen [2005]).