Figure 1 - , the Crown Fire Burned on the Ridge West of Los Alamos
Hello all--
I'm off to NWT for my annual crown fire pilgrimage and wanted to get you a summary of my Los Alamos fire destruction examination. So here it is--
I arrived at Los Alamos on May 14, 2000 to conduct an examination of the home destruction associated with the Cerro Grande Fire. My examination occurred between the afternoon of 5/14 and late afternoon on 5/16. I had contact with the southern command post incident mgmt team, the Los Alamos FD, and the Santa Fe NF.
The homes were destroyed as the main body of the Cerro Grande Fire burned past Los Alamos to the north-northeast and then toward the northeast between about 1700 on 5/10 to the early morning hours of 5/11. About 200 homes were totally destroyed or are irreparably damaged. Although fire suppression actions saved homes, the high ignitability of most of the residential area allowed numerous simultaneous house fires that quickly overwhelmed the suppression forces.
Although the Cerro Grande Fire burned as an intense, continuous and active crown fire in certain areas, within several hundred yards or more of the Los Alamos residential area it burned as a surface fire--an underburn. As you can see in the pictures, the tree canopy was variably scorched but not consumed. In the Figure 1, the crown fire burned on the ridge west of Los Alamos. Figure 2 shows the under-burn as it comes from the wildland in the background towards the residential area where it commonly burned into heavier residential fuels such as woodpiles (bottom left), flammable shrubs, heavy pine needle beds, homes, etc. (Figure 3 shows the under-burn within the residential area with scorched but unconsumed tree canopies. The trees in the foreground did not under-burn, but the house to the left was totally destroyed.
Figure 1 - , The crown fire burned on the ridge west of Los Alamos
Figure 2 - The under-burn as it comes from the wildland in the background towards the residential area where it commonly burned into heavier residential fuels such as woodpiles (bottom left), flammable shrubs, heavy pine needle beds, homes, etc
Figure 3 - The under-burn within the residential area with scorched but unconsumed tree canopies. The trees in the foreground did not under-burn, but the house to the left was totally destroyed.
These homes were totally destroyed with the tree canopies leading up to and adjacent to the structures remaining unconsumed. Canopy consumption adjacent to homes occurred from the burning houses. With the exception of two local and limited areas where trees torched, this is the common scene of home destruction. In Figure 4 note the remaining wood rail fence at the edge of the forest beyond the destroyed home. (Figure 5) The unconsumed vegetation surrounding destroyed homes at Los Alamos indicates that these homes were exposed to a low intensity surface fire, not a high intensity crown fire. Many of the homes destroyed, particularly the 4-plexes on the northwest side (Figure 6), occurred from structure-to-structure spread (comm. w/ LAFD). In general, the wildfire flanked past the residential area. Scattered islands of destroyed homes at the community margin suggests low firebrand exposures and low spotting potential during the late night and morning hours during which much of the residential area burned.
Figure 4 - Note the remaining wood rail fence at the edge of the forest beyond the destroyed home.
Figure 5 - The unconsumed vegetation surrounding destroyed homes at Los Alamos indicates that these homes were exposed to a low intensity surface fire, not a high intensity crown fire.
Figure 6 - Many of the homes destroyed, particularly the 4-plexes on the northwest, occurred from structure-to-structure spread (comm. w/ LAFD). In general, the wildfire flanked past the residential area. Scattered islands of destroyed homes at the community margin suggests low firebrand exposures and low spotting potential during the late night and morning hours during which much of the residential area burned.
My examination suggests that the high ignitability of Los Alamos was principally due to the abundance and ubiquity of pine needles, dead leaves, cured vegetation, flammable shrubs, wood piles, etc. adjacent to, touching and/or covering the homes. Discussion with the Los Alamos FD indicated that few wood roofs existed and thus were not a significant factor. Figure 7 shows a severe condition but not an unusual one. The tree canopy, shrubs, pine needle bed, and wood pile adjacent to and touching this home was common. I think a principal contributor to destruction was the abundance of accumulated pine needles due to the surrounding ponderosa pine canopy. Figure 8 shows the accumulated pine needles that burned off the gravel and composition shingle roof--yes, that's right, a roof surface fire. The destroyed neighboring home is in the background. Again, the vegetation fire in this area (within the community) remained on the surface as a relatively low intensity fire. Examination of surviving homes adjacent to the destruction area indicated that a low intensity surface fire in pine needles could burn to the home and ignite the wood siding prevalent in the area. In several cases, a scratch line that removed pine needles from the base of a wood wall kept the house from igniting.
Figure 7 – Notice the abundance and ubiquity of pine needles, dead leaves, cured vegetation, flammable shrubs, wood piles, etc. adjacent to, touching and/or covering the homes
Figure 8 - Accumulated pine needles that burned off the gravel and composition shingle roof.
The Cerro Grande Fire burning to the community was a surface fire. Figure 9 shows a landscape scene with evidence of the crown fire in the distance and a surface burn in the lower half of the photo. This is the Pueblo Canyon area. North Road is evident in the lower portion with the fire on Ridgeway road on the other side of North. Little canopy scorch is evident in this photo although close inspection reveals a few torched trees within the yellow rectangle. Figure 10 shows a portion of the area found in the yellow rectangle. These homes were destroyed from the low intensity surface vegetation fire and spread from adjacent burning homes.
Figure 9 - A landscape scene with evidence of the crown fire in the distance and a surface burn in the lower half of the photo. This is the Pueblo Canyon area. North Road is evident in the lower portion with the fire on Ridgeway road on the other side of North. Little canopy scorch is evident in this photo although close inspection reveals a few torched trees within the yellow rectangle.
Figure 10 - A portion of the area found in the yellow rectangle. These homes were destroyed from the low intensity surface vegetation fire and spread from adjacent burning homes.
Hope this provides useful and interesting information.
Cheers--
Jack
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Jack D. Cohen
Research Physical Scientist
Fire Sciences Laboratory
406-329-4821
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