Lesson Plan

Lahar in a Jar

Lahar from the Jar

Overall Rating

Add your review
Grade Level:
Middle School: Sixth Grade through Eighth Grade
Lesson Duration:
60 Minutes
Common Core Standards:
6-8.RST.3, 6-8.RST.7, 6-8.RST.9
State Standards:
Washington State Science Standard EALR 4 Earth and Space Science - Grades 6-8 Cycles in Earth Systems
Thinking Skills:
Understanding: Understand the main idea of material heard, viewed, or read. Interpret or summarize the ideas in own words. Applying: Apply an abstract idea in a concrete situation to solve a problem or relate it to a prior experience. Analyzing: Break down a concept or idea into parts and show the relationships among the parts. Creating: Bring together parts (elements, compounds) of knowledge to form a whole and build relationships for NEW situations.


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?


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 volcanic hazard in the valleys that head on Mount Rainier. The word lahar is an Indonesian term that refers to any rapidly flowing and gravity-driven mixture of rock, mud, and water that rushes down the slopes of a volcano. Lahars have been known to travel distances of more than one hundred kilometers (60 miles) at speeds of 60 kilometers per hour (40 miles per hour).

While many scientists treat the terms lahar and debris flows synonymously, scientists and officials working at Mount Rainier seek to reduce confusion locally by modifying work usage. They reserve the word lahar for large flows of eruption or landslide origin with potential to travel to densely populated valleys, and use debris flow for much smaller events caused by glacier floods and precipitation, which stay generally within park boundaries.

Once witnessed, lahars and debris flows are seldom forgotten

The ground shakes and rumbles in a way similar to that of an approaching train. Dust plumes rise into the air above the flow front and small pebbles splash skyward. The flow, tan or gray in color, looks and behaves like a river of flowing concrete. Boulders crush and grind vegetation, which releases a strong stench of organic oils that hangs in the air long after the event is over. Where valley walls widen, lahars spread, drain, and cease motion. Boulders and trees that had been buoyed and pushed to flow margins come to rest as blocky ridges along the flow's margin.

The speed of a lahar and debris flow depends upon its volume and the slope gradient. Some of the faster flows have been clocked at speeds of 30 to 60 kilometers per hour (20 to 40 miles per hour). Lahars may last for hours or days; debris flows generally last for half an hour to several hours. Both leave behind an inhospitable surface of tightly-packed mud, boulders, and vegetative debris.

Abundant water and rock debris make Cascade volcanoes highly susceptible to lahars and debris flows

Eruptions have built vast volcanic slopes at high elevation that are scattered with lava fragments and that retain snow and glacier ice. Mount Rainier's slopes are covered by approximately 4.4 cubic kilometers (one cubic mile) of snow and ice, an amount equivalent to that on all the other Cascade volcanoes combined!

Most lahars form during volcanic eruptions, but landslides can also produce lahars

Almost all lahars happen during volcanic eruptions when hot pyroclastic flows and lava flows interact with snow and ice. This scenario repeated at Mount Rainier many times has resulted in thick sequences of lahar layers beneath the floors of some valleys.

Not to be discounted are large landslides, known as flank collapses, that can also produce lahars. The largest landslide-induced lahars have occurred during eruptive periods and involved rock that had been weakened by long-term exposure to hot acidic groundwater, a process called hydrothermal alteration. 

What triggers a flank collapse? Accepted mechanisms include instability at the onset of or during volcanic eruptions, large earthquakes, and intense ground deformation by rising magma and perhaps long-term exposure to gravity. While the chance of a flank collapse is greatest during eruptive periods, the possibility exists of failure during non-eruptive times. 
Rocks at the head of the Puyallup River valley are more prone to landslides than rocks elsewhere on Mount Rainier, because they contain hundreds of millions of cubic meters (cubic yards) of hydrothermally altered and weakened rocks. At least seven landslide initiated lahars have covered valley floors in the southern Puget Sound area over the past six thousand years. 

Small events caused by rainfall and glacier floods

Conditions that favor debris flow formation are glacier outburst floods in mid-summer and intense rainfall in late fall. These events are small when compared to lahars produced during eruptions, having a thickness of only tens of meters (feet) and traveling only a few kilometers (miles) from their source. Lahars can reach a thickness of 100 meters (300 feet) or more and travel far from the source. Debris flows happen once or twice a year at some Cascade volcanoes, whereas lahars happen much less frequently. 

What to do if in danger from a debris flow or lahar

Most large-volume lahars are associated with volcanic unrest and eruptions. Usually earthquakes or other precursory activity at a volcano serve as a warning than an eruption is imminent. While debris flows happen frequently and large volume lahars happen infrequently, the necessary response is the same. Get to high ground off the valley floor. 


*Print a copy of the teacher pages for your own use. 

*Decide if you are going to do a large group demonstration or have the students work independently or in small groups.  

*Make one copy for each student of "student page Lahar in a Jar".

*Optional: make copies of "Significant Lahars at Mt Rainier" for more information on recent lahars.

*Get together the following student materials for each group or one set if class demonstration:

  • 100 ml or larger graduated cylinder
  • Wide-mouth 1 liter beaker
  • Large wooden spoon or paint stirrer
  • 200 to 400 ml of lahar deposit or rock debris, as prepared in accompanying recipe
  • Calculator
  • One-meter (three-foot) long flat board or gutter 

*Decide whether to project graphics for the class or to hand out copies of graphics to each student. The graphics to be project or copied are:

  • Graphic “Three Prominent Lahars at Mount Rainier”
  • Graphic “Mount Rainier and Emmons Glacier”
  • Graphic “Extension Maps of Lahar Hazard Zones”
  • Graphic “Debris Flow on Tahoma Creek, 1986”
  • Graphic “Mount Rainier Lahar Hazards Zone”
  • Graphic “Tahoma


Instructions and questions for students for Lahar in a Jar experiment.

Download Student Page: Lahar in a Jar

Instructions and answers for teachers for Lahar in a Jar experiment.

Download Teacher Page: Lahar in a Jar

Photo of a 1988 debris flow along Tahoma Creek

Download Graphic: Debris Flow on Tahoma Creek, 1988

Map of lahar hazard zones near Mount Rainier.

Download Graphic: Map of Lahar Hazard Zones

Extension maps of potential lahar hazard zones near Mount Rainier.

Download Graphic: Extension Maps of Lahar Hazard Zones

Photo of the Emmons Glacier on Mount Rainier.

Download Graphic: Mount Rainier and Emmons Glacier

Photo of damage to Tahoma Creek after 1988 debris flows.

Download Graphic: Tahoma Creek after debris flows, 1988

Graphic map of three prominent lahars in Mount Rainier's history.

Download Graphic: Three Prominent Lahars - Map

Teacher should use this recipe to prepare for the "Lahar in a Jar" activity.

Download Lahar Recipe

For teacher use or student use to give background on lahars at Mount Rainier.

Download Significant Lahars at Mount Rainier

Lesson Hook/Preview

*Show the students two videos without context or preparation. Ask students to watch each video twice. The videos are: 
  • Lahars in Japan 2009-2012: https://www.youtube.com/watch?v=kznwnpNTB6k 
  • Lahars in New Zealand 2007: https://www.youtube.com/watch?v=5x5tZAHEoRU
*During the first viewing, ask students to just watch. During the second viewing, ask students to write down any words, descriptions, or phrases that come to mind as the watch the videos. 
*Ask students to share their observations and thoughts. Then, ask students where and what the videos were showing. Reveal that the videos were both at volcanoes, one in Japan and one in New Zealand, and the name for the mudflow they witnessed is a "Lahar". 
*Tell students that today they will be finding out how lahars occur and whether they occur at Mount Rainier. 


Introducing Lahars and Debris Flows: Introduce students to lahars and debris flows through class discussion and graphics, and then conduct the experiment.

1. Instruct students to list some of the distinctive components and characteristics of Mount Rainier that are visible in the photograph entitled “Mount Rainier and Emmons Glacier.” Lead the discussion towards these three features: glaciers, loose rocks, steep slopes. Ask them to explain how volcanic heat, glaciers and snow might interact. Introduce the concept of a lahar as a mixture of rock, mud, and water that rushes down the slopes of a volcano and its river valleys. Rapid melting of snow and ice during eruptions generally cause lahars, though landslides can also initiate them.

2. Instruct students to hypothesize about what happens when an excess of stream water, originating with intense snowmelt in mid-summer or extreme rainfall, flows across valley bottoms strewn with loose rock. Explain that these conditions can lead to debris flows.

3. Instruct students to hypothesize whether or not Mount Rainier is a potential site for lahars. They should explain their reasoning. Reveal the answer that yes, it is the site of frequent debris flows (almost annually). There is an abundance of loose volcanic rock from eruptions and glacier action, and water from snow and ice melt and rain. In addition, rock fall and landslides can initiate lahars.

4. Tell students to use their knowledge of debris flows and lahars to identify the types of terrain over which lahars and debris flows generally travel. Answer: in river valleys.

5. Use the graphic “Tahoma Creek Debris Flow, 1986” to illustrate the appearance of a lahar on Tahoma Creek on the west side of Mount Rainier National Park. Use the graphic “Three Prominent Lahars” to follow the pathway of three major Mount Rainier lahars—Osceola, Electron, and National. These three prominent lahars provide the basis for lahar hazard zones on the graphics “Mount Rainier Lahar Hazards Map” and "Extension Maps of Lahar Hazard Zones."

6. Display the lahar hazards map and ask students which valleys would be affected by lahars and debris flows on each side of the volcano. Ask students to name the communities that are at risk.

7. Explain to students that debris flows tend to happen during intense rainfall and periods of rapid snowmelt at Mount Rainier. By definition, debris flows travel over terrain within the park and do not generally flow beyond park boundaries. Follow the pathway of some recent debris flows.

8.  Determine whether you live, work, or go to school on the debris from one of the lahars shown on the lahar hazard map. Discuss how lahars are significant to your community. Ask students to find the safest locations near their communities.

Make a lahar in a jar: Learn how only a small amount of water in motion can mobilize loose rock to form a lahar. Conduct this activity either as a teacher demonstration or in small groups.

9. Divide class into groups of 3-4 students.

10. Distribute “Lahar in a Jar” student page to each student.  

11. Instruct students to place approximately 400 milliliters of loose lahar material from recipe sample onto a large piece of paper and break up any large clumps of dirt and debris. Dump the loose rock into a beaker. Press it firmly with your hands to remove spaces from between the particles. Record the exact volume on the student page.

12. Ask students to predict how much water they think is required to make the deposit flow like a lahar. 10 ml? 100 ml? More? Students record their prediction on the student activity sheet.

13. Fill the graduated cylinder with water and record the starting amount of water on the student page.

14. Instruct the students to begin pouring water in the beaker in increments of 10 ml.

15. Students should stir the loose rock after each addition of water.

16. After each addition of water, students should tilt the beaker to the side and gently rotate it sideways to determine if the mixture “flows” around the jar sides as a lahar would. The consistency initially is like that of dry dirt, but with the addition of water, changes to the consistency of cookie dough and later to that of thick cake batter. Decrease the amount of water added each time as your lahar begins to flow. Remember, it does not take much water to get debris flowing.

17. Students sum the amount of water used after the rock debris forms a lahar in the jar and record the amount on the student page.

18. Instruct students to compare the total volume of lahar and water and determine the percent water required to produce a lahar in a jar. Ask whether the amount of water was as predicted. Answer: will probably be between 20-40%, depending on the material used. At Cascade Volcanoes, the water content in debris flows and lahars is generally between 30 and 45 percent.

19. Each student group should pour their lahar onto the inclined gutter or board for all of the class to see. Ask for hypotheses about what happens when slope of the gutter or board is changed, then test the hypotheses. Inquire about any interesting observations made of the lahar mixture. The lahar may flow in single or multiple surges. Velocity of the flow increases with slope.

20. Ask students to follow the path of energy transformation, and to write about this, or draw a diagram on the reverse side of their student pages. Students should report that the lahar while still in the jar has potential energy. Kinetic energy is released as the lahar slides down the gutter or board.

21. Ask students what conditions exist on Cascade volcanoes that promote development of lahars. Answers: Loose rock, abundant water, steep slopes, heat.



  • Beaker - a lipped cylindrical glass container for laboratory use.
  • Debris Flow - Also known as a mudslide, is a moving mass of loose mud, sand, soil, rock, water and air that travels down a slope under the influence of gravity.
  • Flank Collapses - is the failure of a large section of unstable slope. Although similar to a landslide, the magnitude of these events is many magnitudes greater.
  • Glacier Outburst Flood - a type of outburst flood that occurs when the dam containing a glacial lake fails.
  • Graduated cylinder - is a common piece of laboratory equipment used to measure the volume of a liquid. It has a narrow cylindrical shape.
  • Hydrothermal Alteration - the mineralogical changes resulting from the deep circulation of hot, pressured and supersaturated groundwater at a late stage in the cooling of a granite.
  • Lahar - a destructive mudflow on the slopes of a volcano.
  • Landslide - the sliding down of a mass of earth or rock from a mountain or cliff.
  • Lava Flow - a mass of flowing or solidified lava.
  • Pyroclastic Flow - a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed.

Assessment Materials

Lahar Volcanic Hazard Warning Sign

Students will create an informational poster that could be displayed at Mount Rainier National Park to describe and explain the hazards of lahars. The purpose of the poster is to inform and warn park visitors.

Lahar Volcanic Hazard Informational Poster

Download Assessment

Supports for Struggling Learners

*Teacher chosen heterogeneous groups for "Lahar in a Jar" activity. 

*Pre-teach vocabulary 

*Highlight and annotate student page "Lahar in a Jar" to ensure comprehension of directions. 

Enrichment Activities

 *Provide students with sand, clay, garden soil and gravel and instruct them to hypothesize about what happens when the amount of clay is increased and decreased. Instruct students to design and conduct experiments with different proportions of materials.

*Obtain rock debris from other sources in your community, such as streambeds, lahar deposits, gardens, etc., and repeat Lahar in a Jar again. Compare results with your lahar recipe mixture. 

*Instruct students to draw a diagram and/or a flow chart that illustrates the initiation and activity of lahars and debris flows.

*Use library and Internet searches to learn more about the lahar history of Mount Rainier and the other snow-clad volcanoes of the Cascades.

*This experiment does not account for the porosity (air space between the particles) of the solids. Instruct students to design an experiment that accounts for porosity.

Additional Resources

Driedger, C.L., and Fountain, A.G., 1989, Analysis of recent glacial outburst floods on Mount Rainier: Annals of Glaciology, 1988, pp. 51–59.

Scott, K.M, Vallance, J.W., and Pringle, P.T., 1995, Sedimentology, behavior, and hazards of debris flows at Mount Rainier, Washington: U.S. Geological Survey Professional Paper 1547, 56 p., 1pl.

Vallance, J.W., and Scott, K.M., 1997, The Osceola Mudflow from Mount Rainier: sedimentology and hazard implications of a huge clay-rich debris flow: GSA Bulletin, February, 1997, v. 109: no.2: p. 143–163, 6 tables.

Vallance, J.W., Driedger C.L., Scott W.E., Diversion of meltwater from Kautz Glacier initiates small debris flows near Van Trump Park, Mount Rainier, Washington: Washington Geology, vol 30, no 1 / 2 July 2002, pp. 17–19.

Walder, J.S., and Driedger, C.L., 1994, Geomorphic change caused by outburst floods and debris flows at Mount Rainier, WA: U.S. Geological Survey Water Resources Investigation Open-File Report 93–4093, 93 p.

Walder, J.S., and Driedger, C.L., 1994, Rapid Geomorphic change caused by glacial outburst floods and debris flows along Tahoma Creek, Mount Rainier, WA, USA: Arctic and Alpine Research, vol. 26, no. 4, pp. 319–327.

Walder, J.S., and Driedger, C.L., 1994, Frequent outburst floods from South Tahoma Glacier, Mount Rainier, USA: relation to debris flow, meteorological origin and implications for subglacial hydrology: Journal of Glaciology, vol. 41, no. 137, pp. 1–10.

Walder, J.S., and Driedger, C.L., 1993, Glacier-generated debris flows at Mount Rainier: U.S. Geological Survey Fact Sheet, Open-File Report 93–124, 2 p.

Zehfuss, P.H., Atwater, B.F., Vallance, J.W., Brenniman, H., Brown, T.A., 2003, Holocene lahars and their by-products along the historical path of the White River between Mount Rainier and Seattle: in Swanson, T.W., ed, Western Cordillera and adjacent areas: Boulder, Colorado, Geological Society of America Field Guide 4, p. 209–223. 

Related Lessons or Education Materials

This lesson plan is part of the "Living with a Volcano in Your Backyard" curriculum, created through a partnership between Mount Rainier National Park and the US Geological Survey Cascades Volcano Observatory.

Contact Information

Email us about this lesson plan