Lecture 2 - WIldfires and Plate Tectonics Flashcards
When was the Fort McMurray fire, and how long did it last?
May 6th, 2016, lasted 458 days (15 months)
What are the requirements to maintain a fire?
Fuel, Oxygen, Heat
What happens to a fire on a windy day?
It spreads faster because it’s being moved around, and as well there is more O2
What are the phases of a wildfire?
- preignition phase
- combustion phase
- extinction phase
What two steps must occur during the preignition phase?
- Preheating: vegetation loses water and other chemical compounds
- Pyrolysis: processes that chemically degrade the preheated fuel (gases, ash, tars, char)
What is required in the combustion phase?
Ignition! - external reactions that liberate heat and light, not a single process but continuing as the fire spreads
What are the two types of combustion?
- Smouldering combustion: lower temps, no need for rapid pyrolysis
- Flaming combustion: higher temp, flames, large amount of unburned material
How does heat transfer work in a wildfire?
Mostly convection, as well as radiation
Why is it neccessary that hot air rises, cools, and sinks again?
Brings in fresh air/oxygen to fuel the fire
What three factors can influence the behaviour of a fire?
- Fuel
- Topography
- Weather (wind)
Fuel?
Smaller fuels burn most readily
Density of trees plays a part: boreal forests of canada are great for fires, close enough trees to light, but not to close to block out oxygen
Topography?
- Drier fuels can be found on south facing slopes or those exposed to winds
- Fire can preheat up hill from the bottom of a valley
Weather?
- Fires spread more quickly under hot, dry, conditions
- Winds greatly influence the spread, intensity, and form of a wildfire
Spot fires?
Little embers blown by the wind start a new fire
What are the two types of wildfires (in terms of what they burn)?
- Surface fires: close to the ground, slow moving
- Crown fires: move rapidly through the crown of a forest by flaming combustion (can be intermittent or continuous)
What happens when fires leave a near surface, water-repellent layer?
Increase of surface runoff/erosion, causes landslides, debris flows, etc.
How does climate change affect wildfires?
Increases the intensity and frequency of fires
What happens when there are severe insect infestations?
Ex. pine beetle: kill all the trees, then the dead, dry wood lights easier and burns faster
Fire weed?
Uses fire to propogate
What are some natural service functions for wildfires?
- increases nutrient content in the soil
- reduces competition for sunlight and rainfall among plants
- some plants (fire weed) need it to spread seeds
What government is in charge of fire management in Canada?
The provinical government, unless the fire is on federal lands
Remote sensing?
Satellite imagery is used to map vegetation and determine fire potential
Fire suppression?
Steer the fire into an area with no fuel (fire break)
Prescribed burns?
Set smaller, controlled fires in order to reduce the amount of fuel for a forest fire
Juan de Fuca plate?
The plate sitting under most of north america, vancouver area
Inner core?
Solid internal core of the earth, high rempt, composed of iron
Outer core?
Liquid, 2000km in thickness, similar composition to the inner core
Mantle?
Solid, 3000km in thickness (THICKEST LAYER), composed of iron-rich magnesium-silicate rocks
Crust?
Outer rock layer of earth, (THINEST LAYER)
Mohorovic discontinuity?
separates the lighter crystal rocks (crust) from the more dense mantle
Lithosphere?
Cool, strong, outermost layer of the Earth (glass)
- includes the upper part of the mantle, and the crust
Asthenosphere?
Hot, slowly flower layer of relatively weak rock (plasticene)
- includes the inner/outer core, lower part of the mantle
Is the oceanic crust or the continential crust thinner/less dense?
Oceanic is thinner but more dense, and relatively new
How does convection work within the earth?
Earth’s internal heat causes magma to heat up and become less dense, then it rises, cools, and becomes more dense (falls back down)
Seismology?
Study of earthquakes
Tectonics?
The large-scale geologic process that deforms Earth’s lithosphere
Is the lithosphere one big slab?
No, broken up into lithosphereic plates which move relative to eachother
Plate boundaries?
Defined by areas of seismic activity
Seafloor spreading?
the growing and shrinking of the seafloor
Spreading at mid-ocean ridges?
New crust is added to the edges of lithosphere plates (divergent plates)
Subduction zones?
Where crust is destroyed along plate edges (convergent plates)
Divergent plate boundaries?
Two plates move away from one another, creating new lithosphere
Convergent plate boundaries?
Two plates collide head on
- result in subduction zones at oceanic-contental collisions OR
- (2) continental collision boundary crumple to make mountains
Transform plate boundaries?
Edges of two plates slide horizontally past one another
- ex. San Andreas Fault
Magnetic stripe?
Rocks on the ocean floor are magnetically striped parallel to mid-ocean ridges, with areas of normal and reverse magnetism
What are the two driving forces for plate tectonics?
- Ridge push (gravitational push away from crests of mid-ocean ridges)
- Slab pull (the weight of the plate pulls a dense ocean plate into the less dense asthenosphere), this is suggested to be the more important mechanisms
Hot spots?
Volcanic centers away from plate boundaries resulting from hot material deep in the mantle
- ex. Hawaiian islands, Yellowstone park
