Investigating the Causes of Wildfires


Wildfire near Hyrum, UT
Showing Fixed-Wing Retardant Drop
Courtesy & Copyright 2013
Holly Strand, Photographer

Fulgurites, caused by lightning
Courtesy Wikimedia Commons,
John Elson, Photographer
Licensed under GNU Free Documentation License v 1.2

Utah Sand Fulgurites
Found on Mount Raymond
Courtesy Utah Geological Survey
Carl Ege, Photographer

Rock Fulgurite (circled)
Found on quartzite at the summit of
Mount Raymond, Wasatch Range,
Salt Lake County, UT.
Courtesy Utah Geological Survey
Carl Ege, Photographer

‘Frozen’ leaves pointing in the direction of prevailing winds during the passage of the fire.
From the ‘Wildfire Origin & Cause Determination Handbook’
Courtesy National Wildfire Coordinating Group(NCGW.gov)

Hi I’m Holly Strand of Utah State University’s College of Natural Resources.

It’s fire season in UT. The hill slopes have turned a parched yellow-brown and the trees look thirsty and flammable. As of Aug. 13, there were 7 fires burning across the state.

One of the first questions that arises with any wildfire is “What started it?”

And I wonder: “How in the world would you figure this out given the destruction that a fire leaves in its wake?”

The first step toward identifying a cause involves finding the exact spot where the fire started. To do this, investigators look for witnesses. And having information on wind direction for the duration of the fire helps a lot. But even in the absence of these, the fire itself leaves clues regarding the direction of movement. And if you know the direction of movement, you can trace the path backwards to the ignition site.

For instance, on a tree or post, the side exposed to the oncoming fire will show deeper charring, more loss of wood and more white ash than the unexposed side.

However the leeward side of a tree may have the highest char mark. That’s because as strong winds blows the fire past a tree, the flames are drawn into the eddy zone on the leeward side and extend higher up the trunk. Still, the deeper char will be on the side facing the advancing flame. So to get to the area of the fire origin, you’d want to follow direction indicated by the most damaged tree face.

When green leaves of shrubs or trees are scorched, they tend to become soft and pliable and bend in the direction of the prevailing wind. After the fire passes they become fixed in this position as they cool, still pointing in the direction of the wind. So the opposite direction of the pointing leaves will take you closer to the fire origin.

Another thing that generally helps fire investigators is the fact that all fires need time to achieve their maximum spread rate/intensity. A newly ignited fire may take 30 min or more to ramp up. As a result even with high intensity fires, the area of initial ignition will show relatively less damage; upper foliage and branches may even remain intact.

Once the area of origin is identified, investigators look for the human or natural source of the blaze. Footprints, tire marks or evidence of a campfire are noted with interest. Nearby power lines, railroad tracks or electric fences may have provided the initial spark. Investigators often end up on their hands and knees searching for things such as cigarette parts, ignitable liquid residue; bullets or empty shell casings.

If lightening is a suspected source investigators look for strike marks or splintered wood fragments. Lightening can also leave a glassy residue, called a fulgurite, when the strike melts sand on the ground or on vegetation.

Thanks to Wesley Page of USU’s Department of Wildland Resources for sharing his wildfire expertise.

For sources and more information on investigating the cause of wildfires go to www.wildaboututah.org

For Wild About Utah and USU’s College of Natural Resources, I’m Holly Strand.

Credits:

Images: Hyrum Fire, Courtesy & Copyright 2013 Holly Strand
Courtesy Wikimedia, John Elson, Licensed under GNU Documentation License V1.2
Also images from Wildfire Origin & Cause Determination Handbook, Courtesy National Wildfire Coordinating Group(NCGW.gov)
Text: Holly Strand

Sources & Additional Reading

Cheney, Phil and Andrew Sullivan. Grassfires: Fuel, weather and fire behavior. 2008. CSIRO. http://www.amazon.com/Grassfires-Fuel-Weather-Fire-Behaviour/dp/0643093834

Wildfire Origin & Cause Determination Handbook. 2005. A publication of the National Wildfire Coordinating Group Fire Investigation Working Team NWCG Handbook 1. PMS 412-1. May 2005. http://www.nwcg.gov/pms/pubs/nfes1874/nfes1874.pdf

Investigating Wildfires: Part One. Interfire online. http://www.interfire.org/features/wildfires.asp
(accessed August 14, 2013)

Investigating Wildfires: Part Two. Interfire online. http://www.interfire.org/features/wildfires2.asp
(accessed August 14, 2013)

Map of current large active wildland fires in Utah.
(accessed August 14, 2013) http://www.utahfireinfo.gov/

Wildfires in Utah

Wildfires in Utah: Click to view larger image of Fireweed growing in burned area, Photo Courtesy US FWS, U.S. Fish and Wildlife Service
Fireweed Grows in Burned Area
Photo Courtesy
U.S. Fish and Wildlife Service

Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.

Prior to settlement by the pioneers at the end of the 19th century, wildfires were relatively common throughout the mountains of Utah. Wildfires were a result of natural disturbance, such as lightning strikes, but many were purposely set by Native Americans. Wildfires restarted the cycle of forest succession and also created a mosaic of plant communities across the landscape.

Although Utah’s changing climate has had a major influence, human factors have considerably altered the natural fire regime over the past 150 years. Fire frequency slowly declined prior to settlement by the pioneers due to a period of global cooling; however, fire activity increased considerably to its highest point during the settlement period between 1856 and 1909. This increase was linked to the dramatic growth in human population and activity, which lead to increased surface fuel from extensive timber harvesting, and inevitably to more ignition sources for more frequent fires.

Between 1910 and 1990, there was a dramatic decline in wildfires throughout Utah, despite the gradual increase in global temperatures. This was due to intensive livestock grazing, habitat fragmentation as a result of development, agricultural expansion, and effective fire suppression. As a result, shade-intolerant trees that relied on fire for regeneration, such as aspen and lodgepole pine, were often replaced by long-lived, shade-tolerant trees, such as spruce and fir. In general, this resulted in a gradual decline in diversity of plant communities.

As a result, more homogenous forests that are densely populated with trees and accumulated fuels are more susceptible to intense fires that burn hotter and are more difficult to control. In 2007, Utah had a record-setting fire season that burned over 629,000 acres, including the 363,000-acre Milford Flat Fire. We’re halfway through the fire season this year, and approximately 400,000 acres have burned in Utah, costing over $47,000,000 to control. Additionally, wildfires that have burned about three-quarters of the acreage this year were classified as large in size. It seems that increased temperatures, decreased snowpack, and a century of land use and management has resulted in a dangerous wildfire situation in Utah and much of the West. It will take some creative management strategies, such as sustainable timber harvesting or prescribed fires, to tackle this ongoing issue if we want to limit the risk and cost of larger and more frequent wildfires.

For Wild About Utah, I’m Mark Larese-Casanova.

Credits:

Images: Courtesy U.S. Fish and Wildlife Service, images.fws.gov

Text:     Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
Additional Reading:

Madany, M. H., and N. E. West. (1983). Livestock grazing-fire regime interactions within montane forests of Zion National Park, Utah. Ecology 64:661-667., http://www.jstor.org/discover/10.2307/1937186?uid=3739928&uid=2&uid=4&uid=3739256&sid=21100946519023

Neugebauer, C. (Jul 15, 2012). Burning through money: the cost of Utah wildfires. Salt Lake Tribune., http://www.sltrib.com/sltrib/news/54485976-78/fire-fires-cost-costs.html.csp

Utah Fire Info webpage: http://www.utahfireinfo.gov/

Williams, J., D. Albright, A.A. Hoffmann, A. Eritsov, P.F. Moore, J.C.M. de Morais, M. Leonard, J.S. Miguel-Ayanz, G. Xanthopoulos, P. van Lierop. (2011). Findings and implications from a coarse-scale global assessment of recent mega-fires. 5th International Wildland Fire Conference. Sun City, South Africa., http://www.fao.org/docrep/014/am663e/am663e00.pdf