Anatomy of the Las Conchas Fire, Jemez Mountains,
New Mexico
J. Biggs, Dept. of Natural Resource Management, New Mexico Highlands Univ., Las Vegas, NM
Abstract—New Mexico has experienced a prolonged drought, with increasing temperatures and decreasing
snowpack, since the late 1990s. This has coincided with significant increases in wildfire activity, resulting in
the state’s largest and most destructive fires occurring since 2000. The winter and spring prior to the Las
Conchas Fire in 2011 were among the driest on record. Less than 1 mm of total precipitation was recorded in
the burn area the 30 days prior to fire ignition. Fuel conditions were very dry, with 1 hour fuels at <1 percent
fuel moisture and 1000 hour fuels at <6 percent fuel moisture. The Las Conchas Fire began at 1300 hours
on June 27, 2011, from a tree that fell onto a power line. It burned on multiple land ownerships, including
U.S.F.S., National Preserve, private, and National Park Service property. Fire intensity and spread were driven
by the combination of high topographic and vegetation diversity, fuel conditions, and wind. Deep extensive
canyons dissect the burned area and are surrounded by steep mountain slopes and open expansive grasslands that allowed the fire to spread in multiple directions at varying speeds and intensities. The vegetation
within the burned area was characterized by montane forest, grasslands, and shrublands in higher elevations, and shrubland, grassland, and woodland at lower elevations. Within the first two days of the fire,
spread occurred in multiple directions extending south, east, and north; typical directional spread was to the
northeast, driven by usually southwest winds. During the first five days of the fire, maximum temperatures
averaged 28°C and minimum temperatures averaged 7°C; humidity ranged from 15 to 67 percent throughout
the 5-day period (including evenings). Average wind speeds were 2.7 ms-1 and maximum winds averaged
12.5 ms-1. At the time of ignition, atmospheric conditions were unstable, resulting in strong winds at both the
surface and aloft (40 mph gusts at 20 ft); the temperature was approximately 32°C with very low humidity.
During the first 14 hours, fire behavior was erratic and fast-moving, burning approximately 43,000 acres at
a rate-of-spread of about 1 acre per second. Flame lengths were >300 ft., including during evening hours.
Over two weeks, it grew to 156,000 acres and was New Mexico’s largest fire until 2012. The fire was largely
wind-driven over the first two days, becoming more plume-dominated thereafter. Two critical burn events
took place that were characterized by extreme plume formation and collapse, and extreme fire behavior in
an upper watershed. The high severity of both these episodes later resulted in severe post-fire flood events.
Based on observed intensity, severity, and behavior, the Las Conchas Fire was out of the historic range of
variability when compared to other large fires.
Keywords: Las Conchas Fire, Behavior, Fuels, Flame
In: Keane, Robert E.; Jolly, Matt; Parsons, Russell; Riley, Karin. 2015. Proceedings
of the large wildland fires conference; May 19-23, 2014; Missoula, MT. Proc.
RMRS-P-73. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky
Mountain Research Station. 345 p.
USDA Forest Service Proceedings RMRS-P-73. 2015.
The content of this paper reflects the views of the authors, who are responsible for the
facts and accuracy of the information presented herein.
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