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Saturday

Hot
Hot
High: 102 °F
Low: 67 °F

Sunday

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Low: 64 °F

Monday

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Mostly Sunny
High: 93 °F
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SCV Outdoor Report: Part 3 - Aftermath Of A Wildfire:

What happens
after the flames die down, the smoke dissipates and the news crews go home.

by Wendy Langhans

My husband has a knack for
making the best sandwiches:  sliced
turkey from the deli counter, red-leaf lettuce and, of course, fresh
tomatoes.  All of this he carefully wraps
in wax paper.  He claims
that, unlike sealed plastic bags, loosely-wrapped wax paper keeps the sandwich
moist but not soggy.

 

You see this principle at
work in our chaparral:  the top outer
surface of leaves often have a waxy coating, while the underside does not.  The waxy coating protects the leaf against
the drying rays of the hot sun, while allowing the uptake of carbon dioxide and
the release of oxygen on the shaded underside. 

 

But what happens to this
waxy coating during a wildfire?  It is
vaporized and later deposited on the surface of the soil, creating what is
known as hydrophobic (water repelling) soil.

 

To understand how this
works, we have to look at two physical properties of water.  The first is cohesion, how water
molecules are attracted to each other. 
This creates surface tension, which is why water droplets “bead up” and
liquids “creep up” the side of the measuring cup.

Image
Water droplets bead up due to surface tension

 

The second property is
adhesion, how water molecules are attracted to other substances.  We observe this property when we see an
errant water spot on a silk shirt (which, in my experience, always happens
right before you leave the house to go to a party).

After a wildfire, the
surface of the soil is coated with a waxy substance, which weakens the soil’s
adhesive properties.  This makes the
cohesive forces of rainwater stronger than the adhesive forces of water with
soil.  So the soil surface repels
water.  And water, of course, runs
downhill.

Image
Close-up view of soil evidence of runoff

 

Add a third physical
property - the force of gravity on a steep slope - and you have the recipe for
a mudslide or debris flow.  This is one
reason why, during a heavy rainstorm, we evacuate downslope of a burn area.

 

Image
Hillside in Wilson Canyon after the Sayre Fire

 

To learn more:

 

An older but still useful
overview from the CA State Coastal Commission. “Natural History of Fire &
Flood Cycles”:

http://www.coastal.ca.gov/fire/ucsbfire.html

 

An article on hydrophobic
soil:

http://www.cnr.uidaho.edu/extforest/F5.pdf

 

The emergency assessment
of the Sayre fire is scheduled to be released later this month, but here’s an
assessment from last years Buckweed Fire.

“Emergency Assessment of
Debris-Flow Hazards from Basins Burned by the 2007 Buckweed Fire, Los Angeles County, Southern
California”:

http://pubs.usgs.gov/of/2007/1414/

 

__________________________________________________________

 

Upcoming Outdoor Events: 

 

Save the date - January 24, 10-12
AM.  Fire Ecology Hike in Wilson
Canyon.

Heavy rain cancels - call
the day before to confirm (310-858-7272 x 115). 
For map and directions go here.

Sponsored by the Mountains
Recreation and Conservation Authority.

 

Saturday, December 20, 8:00-10:00
AM.  Morning Bird Hike in Towsley
Canyon.  Towsley Canyon is a year-round home for birds. 
They like our Mediterranean climate, the local bounty and the California sunshine. 
Bring your binoculars and meet at the entrance.  Heavy rain cancels.  For map and directions go here.

Sponsored by the Mountains
Recreation and Conservation Authority.

 

Saturday, December 20, 2:30-4:30
PM. 
Get-the-kids-out-of-the-house walk in Pico
Canyon.

Do you need some time wrap
presents without little eyes spying. 
Send the kids out with a visiting relative for a taste of nature - the
real glitz. Heavy rain cancels.  For map
and directions go here.

Sponsored by the Mountains
Recreation and Conservation Authority.

 

Saturday, December 27th, and every Wednesday, 8:00 AM. 
Trail Maintenance Volunteers at Towsley
Canyon
.

Come join our trail
maintenance volunteers for camaraderie and a heart-thumping workout.  For
more information contact Steve Ioerger at 661-291-1565.

 

//////////////////////////////////////////////////////////////////////

 

You can listen to stories
like this every Friday morning at 7:10 a.m. on "The Hike Report", brought to you by your hometown radio
station KHTS (AM1220) and by the Mountains Recreation and Conservation
Authority.

 

For the complete MRCA hike
and activity schedule and for trail maps, click here or go to www.LAMountains.com.