lecture #12- Wildfires Flashcards
How do wildfires start?
From lightening and Volcanic eruptions
What happens after a fire?
The vegetation completes its life cycle form early colonizing to mature ecosystem
Which trees are have fire resistant bark?
redwoods and Oak
Why are we seeing an increase in wildfires through geologic time?
Warmer and dryer climate
Increased use of fire by human for clearing land and for heat, cooking etc
What are the requirements for a wildfire?
Fuel, O2, heat
-if anyone of these are lost, it will dissipate
What is the relationship between plants (CO2) and fires?
Plants take in and store CO2 from the atmosphere, so when they get burned they release it back into the atmosphere
What are the 3 phases of wildfires?
Pre-ignition
Combustion
Extinction
What is the pre-ignition phase?
Vegetation reaches a tem at chic it can ignite
-water leaves vegetation
What is pyrolysis?
chemical process describing the degradation of a large hydrocarbon molecule into smaller ones
-occurs in the presence of heat
What is the combustion process?
Phase begins with ignition
Ignition is not a single process, it can occur repeatedly as the fire moves
-pyrolysis and pre-heating results in fuel
What is Flaming combustion?
The rapid, high temp conversion of fuel into heat
-flames and large amounts of unburned material
What is smouldering Combustion?
Occurs in areas with burned material and ash that covers new fuel
What are the 3 transfers of heat?
Conduction (molecule to molecule)
Radiation (invisible waves)
Convection (liquid or gas)
What happens to air as its heated?
it rises and become less dense and rising air moves heat from the zone of flaming and is replaced with fresh air to fuel the fire
what is the extinction phase?
Time when the combustion has ceased
-no longer sufficient fuel
What kind of fuel burns easily?
Dead or diseased organic material
Which orientation of the sun causes the slopes to be drier than others?
South
Which orientation of the wind causes the slopes to be drier than others?
West
Why is wind bad?
Can help pre heat material
Can cary embers to other places, spreading the fire
Which geographic region is most at risk of wild fires?
Changes form year to year depending on the weather and which areas are experiencing the most drought
YellowStone 198 Case study
- Had a policy to let natural fires burn out
- really hot summer and public pressure to put the fire out
- it couldn’t be controlled by the crews and burned for months because of the previous policy to put out all fires
- Revitalized the ecosystem
What is a Surface fire?
They travel close to the ground and burn shrubs leaves twigs grasses
-move relatively slow
What is a crown fire?
Move rapidly through the forest canopy by slamming combustion
- fed by surface fires that move up limbs or tree trunks
- driven by strong winds
- can have intermittent (can consume tops of trees in an area) or continuous crown fires (can consume tops of all trees)
What kind of layer do fires leave behind?
hydrophobic layer
- caused by the accumulation of chemicals from burning vegetation
- increases surface run off and erosion
- can persist for several years
