Wednesday, August 14, 2013

Wildfire Videos and Photos

Fire is on the landscape of northern Utah.  The Rockport 5 fire sparked yesterday quickly grew into a beast that destroyed 13 homes.  

Wildfire behavior is strongly influenced by three components summarized in the Fire Triangle below: Fuels, Topography, and Weather.

Source: Southwest Environmental Research & Education
Here's a video of the a wildfire that started on Monday afternoon in the Avenues and was quickly put out by heroic fire fighters.  It pretty much shows all three of these components in action.  In particular, note how the flame front movement and intensity increase near the end of the video as the wind (i.e., weather) pushes the flame front into fresh grass (i.e., fuels).   Movement of the flame front down the hill (i.e., topography) probably resulted in a slower fire spread than if the flame front was moving uphill.  Video courtesy of John McMillen.

There are some remarkable photos of the Rockport 5 fire on the Salt Lake Tribune web site.  The one below is from Tribune Photography Steve Griffin, who has taken many remarkable weather related photos over the years.
Source: Steve Griffin/Salt Lake Tribune
The processes responsible for producing these whirls are similar to those that generate dust devils.  Strong surface heating, which can be quite intense during a fire, generates an updraft that stretches and concentrates rotation in the atmosphere in much the same way that an ice skater that stretches their body begins to spin faster.  The initial source of rotation can be vertical wind shear near the earth's surface, which gets tilted and stretched in the vertical by the updraft.  In the case of the Rockport 5 fire, horizontal wind shear generated by flow interaction with topography could have played a role.  Fire whirls are believed capable of producing winds comparable to those found in EF0 or EF1 tornadoes (EF here standing for the Enhanced Fujita Scale for Tornado Damage).

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