What are lahars and why are they the greatest volcanic hazard at Mount Rainier? Objective Explore how small amounts of water can mobilize loose rock to form lahars by making a small lahar within the safety of a beaker or jar and analyzing it using scientific methods. By the end of the lesson, students will be able to answer the question: What are lahars and why are they the greatest volcanic hazard at Mount Rainier? Background Lahars are fast flowing torrents of rock, mud, and water Lahars, also known as volcanic mudflows or debris flows, are worthy of attention because they are the principal Duration: 60 Minutes.