Reducing risk from lahar hazards: concepts, case studies, and roles for scientists

Table 1 Examples of lahar travel times from lahar source areas (points of initiation) to selected locations in downstream river valleys

Lahar date	Specified locations	Lahar trigger	Distance of specified location from lahar source (km)	Travel time from lahar source to specified location (min)	Average speed (meters per second)¹
1926	Points along Hurano River, downstream of vent at Tokachidake volcano, Japan	Eruption (pyroclastic density current on snow and ice)	2.4	1	42
			6.4	4	26
			20.0	17	16
			23.2	29	5
1980	Points along Pine Creek, downstream of vent at Mount St. Helens, USA	Eruption (pyroclastic density current on snow and ice)	10.1	7	24
			14.1	11	16
			16.8	13	18
			20.9	19	14
1985	Point along Denjo River, downstream of landslide at Mount Ontake volcano, Japan	Earthquake-triggered slope failure	11.4	10	19
1985	Points along Río Chinchiná, downstream of vent at Nevado del Ruiz volcano, Colombia	Eruption (pyroclastic density current on snow and ice)	11.3	20	10
			33.0	70	7
			68.6	172	6
1990	Points along Drift River, downstream of vent at Redoubt Volcano, Alaska	Eruption (pyroclastic density current on snow and ice)	7.6	8	16
1990		Eruption (pyroclastic density current on snow and ice)	18.5	27	10
1994	Points along Río Páez, downstream of vent at Nevado del Huila volcano, Colombia	Earthquake-triggered slope failures	4	2 to 3	22 - 33
			9	6 to 9²	17 - 25
			30	20 to 30²	17 - 25

Travel times are partly a function of lahar magnitude and are determined from eyewitness accounts, instrument recordings, and back-calculations of flow velocity based on physical evidence. Data from Pierson ([1998]) and Scott et al. ([2001]).
¹Average speed is computed from the closest upstream point where timing information was available; not all timing points shown in this table. Localized lahar velocities tend to decrease as channel slopes decrease with distance downstream.
²Lahar could be heard or felt about 5 minutes before its arrival at this point.

ISSN: 2191-5040