Lahars (Debris Flows)


-Paul Kimberly, United States

-Gerardo Carrasco Núñez, Mexico

-Tom Pierson, United States

-Scott Rowland, United States

-Claus Siebe, Mexico


Lahars are rapid, sometimes catastrophic floods of dense mixtures of rock debris and water, that occur in streams that flow from volcanoes. They occur when heavy rainfall or lake-outbreak water floods mix with loose volcanic rock fragments, in sizes ranging from microscopic clay particles to large boulders. In the last decade such flows have caused the deaths of tens of thousands of people. Between 1979 and 1983, lives and property were lost at El Palmar due to lahars from Santa María volcano, and a number of towns, roads, bridges, and agricultural areas are still at risk from future lahars of Santa María.


*Assess and designate areas that are at risk from future lahars.

* Understand the past history of Santa María lahars, in order to predict lahar size and how often they will occur. Studies should determine the worst-case scenario.

* Provide for effective lahar hazard mitigation.


1) Assess and mitigate hazards due to lahars.

A) Prepare a lahar-hazard map.

1) This would identify areas, population, and infrastructure most at risk.

B) Develop ways to monitor conditions leading to lahars.

1) Measurement of rainfall intensity and duration.

2) Periodic measurements of river channel conditions.

3) Observation and assessment of potential source material originating from the Santiaguito dome complex.

C) Develop ways to monitor lahar occurrence.

1) Develop an effective warning system for populations that may be at risk.

2) Regularly monitor the effect of lahars on the channel system.

2) Undertake scientific studies to address critical research needs.

A) Determine hydraulic type and behavior of previous lahars.

B) Resolve size, frequency, and triggering mechanisms of previous lahars.

C) Identify human and institutional resources to carry out studies.

1) Locally supported projects from institutions including INSIVUMEH and CEPREDENAC.

2) Studies supported by outside institutions including graduate student thesis projects.

3) Employment of local citizens to assist researchers in order to improve community awareness.

3) Implement effective communications of hazards information.

A) Educate local residents at risk.

B) Educate local authorities.

C) Educate state and national civil defense organizations.

1) Encourage coordination between scientific community and emergency management agencies.


* Support INSIVUMEH in the preparation of a hazard map.

* Support critical scientific studies needed to understand Santa María lahar hazards including regular channel surveys and rainfall data collection.

* Establish an appropriate warning system for populations that may be at risk.

* Involve local communities in research projects in order to build a network for hazards communication.

* Begin an educational program on lahar hazards for local residents at risk, local authorities, state and national civil defense organizations.

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