The Arizona Geological Survey has teamed up with Arizona Public Media to produce a short story and seven-minute video about debris flows in the Santa Catalina Mountains.
Debris flows are landslides composed of water, rock, soil, vegetation, and anything else that becomes entrained in the slide. The southern face of the Santa Catalina Mountains contain evidence of debris flow as old as 15,000 years, and as recent as the 2006 debris flow in Sabino Canyon.
Debris flow are precipitated by heavy monsoon rains and the mountain slopes are made more susceptible to such flows by being denuded by forest fires. Geologists claim they can predict where debris flow may happen, but not when.
See the story and video here: