What causes wildfires? How do wildfires spread so quickly?

July 2, 2021

Learn about the different causes of wildfires and how they can easily (and quickly) spread

The small flame that causes a wildfire to start and spread.

If you think back to the Texas wildfires of 2011, you might remember just how massive and widespread they were. There were aerial photographs, but the billowing smoke and spreading flames could even be seen from the International Space Station

It's hard to imagine that something so large could have started with something so small; almost all wildfires, no matter how large or destructive they become, begin with something much, much smaller.

But what causes wildfires and how do they get out of control so quickly? Unsurprisingly, it's a complicated process that both humans and nature contribute to. Read on today as we take a look at the various factors that help start and spread wildfires!

What are the different causes of a wildfire?

In order to understand how wildfires spread, and spread quickly, we need to first understand how they start in the first place. The ingredients for a wildfire are simple: you need fuel, heat, and oxygen. Oxygen is, of course, readily available in the air and the fuel is usually grass, trees, and leaves. The remaining component, heat, can come from a wide variety of sources, some caused by nature, and some caused by humans.

How do humans cause wildfires?

Although wildfires are considered to be a natural disaster, humans are responsible for starting our fair share. In fact, some estimates say that humans are responsible for as many as 90 percent of wildfires in the United States. Intentional acts of arson do occur, but most of the wildfires started by humans are accidental. 

These are some of the more common ways that humans might be responsible for fires that grow into wildfires.  

Utility fires and controlled burns. Whether fire is used to clear land, burn brush, or dispose of trash, there are a plenty of practical uses for controlled burns. However, if the weather conditions are just right, or if the fire isn't properly maintained, these fires can quickly get out of control. 

Industrial processes and accidents. Certain industrial processes can, at times, create unintended fires if something goes wrong. For example, a chemical plant explosion, or even something like an electrical malfunction.

Construction. Drilling, welding, sawing, operating large machinery - there are plenty of processes on a construction site that can potentially start a fire if the conditions are right. However, even small, seemingly harmless tasks can be enough to start a wildfire. For example, in 2018, a wildfire in California was started by a rancher who accidentally sparked dry grass while hammering a metal stake into the ground.  

Damaged infrastructure. Damage to electrical systems, such as power lines, can very easily cause a fire. This is often the result of wind or other weather event, but power lines can be damaged by a collision, or even fail as a result of aging or degradation. 

Vehicles. When drought conditions are severe, almost anything can cause a fire. Cars, trucks, and even trains all have the ability to accidentally spark a fire when the grass next to the road or track is crispy and dry. An engine that catches fire after an accident is an obvious example, but even small sparks caused by braking or wheels scraping the asphalt can and do cause wildfires. 

Smoking and cigarette littering. Although this might seem rather specific, many fires start when people carelessly dispose of their cigarettes out their car window. This is especially problematic during the dryer times of the month when the medians and margins on the side of the road are filled with dry, dead grass. Even the small ember of a cigarette can be enough to cause a wildfire. 

Grills, campfires, fireworks, and other outdoor activities. BBQ grills are almost a mandatory component to any holiday or outdoor activity, and it's hard to imagine a good camping trip without a campfire. Similarly, many celebrations, like the 4th of July, feature all kinds of foods cooked on an outdoor grill. A wayward ember, a forgotten fire, or a stray sparkler can easily be the start of a seriously destructive wildfire. 

What are the natural causes of wildfires?

There are plenty of ways that wildfires can start naturally, but some are more common than others. However, as we'll discuss in a moment, some of these causes are somewhat of a combination; they involve both man-made variables and natural phenomenon. 

Lightning. By far the most common source of naturally occurring wildfires is lightning, specifically cloud-to-ground lightning. We often think of lightning in relation to storms that dump rain down, but that's not always true. Low-precipitation thunderstorms may shower the ground with lightning and not let loose as much as a drop of rain. Even when there is rain, it may not always be enough to extinguish the resulting fire. Additionally, lightning can strike miles away from the storm itself, meaning there is not always the benefit of rain to stop a possible fire. 

Wildfires caused by lightning tend to burn more land than fires humans are responsible for starting. Fires that humans cause generally start closer to settlements, making it easier to spot, report, and extinguish before it gets out of control. However, when lightning starts a fire in the middle of nowhere, it often grows to a substantial size before emergency responders have the ability to deal with it. 

Geological activity. While Texas was once a hotspot for geothermal activity, in modern days this is no longer a concern. However, there are plenty of places in the US where geothermal activity, like volcanoes, can cause fires.

Coal-seam fires are an interesting geological phenomenon where seams of underground coal catch fire and burn for long periods of time, sometimes thousands of years. Although the majority of these fires take place beneath the surface, they can find their way above ground and cause fires to ignite in forests and grasslands. 

Indirect natural causes. Natural disasters, such as wind, tornadoes, and earthquakes, don't cause wildfires directly, but can create fires as a secondary effect when they damage or destroy utilities, such as power and gas lines. 

Spontaneous combustion. Although rare, spontaneous combustion can start fires that seem to spark out of nowhere, or with no apparent cause. Of course, there is a cause and it is usually a runaway exothermic reaction, or a chemical reaction that produces heat. 

There are a number of farming practices that can cause spontaneous combustion through bacterial fermentation. For example, bacteria within piles of wet hay can produce enough heat to start fires. But there are also examples of spontaneous combustion that happen independently of any human activity, such as the aforementioned coal-seam fires. 

How do wildfires spread? 

Once a wildfire has started, it seldom stays put for long. There are a number of ways in which a small fire becomes a much bigger fire as it spreads, searching for new fuel sources. 

Vegetation and terrain. One of the more obvious contributors to the spread of a wildfire has to do with where it begins, or more specifically, what the land around it looks like. A fire that begins in a dry patch of an otherwise lush landscape isn't likely to spread. On the other hand, if the area around it is filled with dry grasslands, it will spread like, well...like a wildfire. 

Depending on the weather conditions, natural barriers like rivers can actually prevent a wildfire from spreading beyond a certain point. On the other hand, large open areas or contiguous forests may allow a fire to continue to spread. 

Wind. The wind is another major factor in how a wildfire spreads. A fire burning in an area with still winds will seemingly crawl forward, which can give firefighters the opportunity to stop it from spreading. If the wind picks up, however, it can virtually sprint forward

There are also certain cyclical weather patterns that can cause a wildfire to spread further and faster. In California, the Santa Ana winds blow westward, bringing warm dry air that can fan and spread wildfires. Similarly, La Niña can bring warm weather and strong winds to Texas every so often.

Embers. Although embers rely on wind, they cause wildfires to spread in a different way than just the wind by itself. Embers are like little coals, hot enough to start a fire but light enough to ride the breeze. If the conditions are right, embers can cause a wildfire to leapfrog from place to place, causing it to spread without the flames actually having to get there first. 

Embers are especially dangerous because they can ride currents on, under, and into your home. This is why it is incredibly important to consider taking steps to harden your home. 

Setting the stage: Droughts, wildfire season, and favorable conditions for wildfires

As we discussed, there are plenty of ways for a wildfire to spark, both natural and artificial. But it often takes more than a spark or source of ignition for a small, localized fire to become a wildfire. The environmental conditions play a large role in both the start and spread of wildfires.

Specifically, when a particular environment becomes hot and dry, the vegetation begins to dry and eventually dies. In many regions, this is a seasonal cycle; just like hurricane season or tornado season, there is often a wildfire season, or a particular time of year where the risk of a wildfire starting and spreading is higher than the rest of the year. 

In normal or ideal circumstances, this season is followed by a season of rejuvenation categorized by cooler temperatures and increased rainfall. However, because of gradual changes in the climate, droughts are beginning to drag on. As average temperatures increase and annual rainfall decreases, vegetation dries and dies, and in some places, it's wildfire season almost year-round. 

The longer that the conditions remain favorable for wildfires, the greater the chances that something will start one are, whether it be a bolt of lightning, an unattended campfire, or even the sparks from your brakes. 

That's why it's important to make sure that you do all you can to prevent wildfires! 

What can you do to stop the spread of wildfires? 

At the risk of sounding like a certain bear, only you can prevent forest fires! Well, not only you, but you can certainly help. By following some of the simple steps below, you can do your part to stop the spread of wildfires by preventing them from starting in the first place. 

Be mindful of environmental conditions when starting fires. Pay attention to burn bans. If you're burning brush, or otherwise performing a controlled burned, it's a good idea to check the weather forecast beforehand. You should also try and choose to perform the burn during a time of year when the grass or vegetation around you isn't dry. Check with your local authorities to ensure that your county or city isn't under a burn ban.

Lastly, it's always a good idea to call your local fire department or sheriff's office to let them know you're performing the burn. If it does get out of control, they should be able to respond faster to help contain it. 

Always be prepared to put a fire out. If you're monitoring a fire, make sure to have implements on hand to extinguish it if it gets out of control. This could include a reliable water source, fire extinguisher, a shovel, and so on. 

Don't mess with Texas! Always properly dispose of cigarette butts and make sure they are completely cool before putting them in the trash. 

Make sure your fire is extinguished. Simply covering a campfire with sand isn't enough. It will put out the flames, but coals can stay hot enough to start a fire for hours after. Dump water on it, stir, and hold your hand above it to check for heat. If it is cool enough for you to safely place your hand on, then you can be certain it won't come back to life. 

Watch the flames. Whether you're grilling, burning, or camping, never leave a flame or coals unattended. If you have to step away, make sure that someone is available to watch it and if needed, put it out. 

Choose a safe location. Make sure your grill or fire pit is away from your house, trees, and avoid burning over dry areas. If necessary, use a shovel or rake to clear the ground around your fire or grill and remove dry grass, sticks, and leaves. When you're done, make the coals are extinguished and place the ashes in a fireproof container. 

Harden your home and create defensible spaces. Take steps to make your home and property more resilient to a possible wildfire. Regularly clear dead vegetation from your lawn and your roof. Place screens over your vents and beneath your deck to prevent embers from floating in and catching fire. When possible, replace or upgrade flammable components of your home with ignition resistant materials. Keep your lawn watered and trimmed. Trim trees at least six feet above the ground and clear smaller vegetation from beneath. 

For more information about home hardening and creating defensible spaces, check out our blog here!

A wildfire spreading through dry trees.

To learn about Germania Insurance and our insurance products, request a free quote online or reach out to one of our Authorized Agents today! 

by Geoff Ullrich

About the Author

Geoff Ullrich is a writer and Content Marketing Specialist at Germania Insurance.