Most wildfires are caused by human actions, such as leaving a campfire unattended or discarding cigarettes. Wildfires can also occur naturally from lightning strikes and erupting lava.
In the United States, 90 percent of wildfires are caused by humans, contributing to a total of 5 million acres of land that burn each year. Most fires begin in drought conditions, when the underbrush in forests is very dry. One spark can ignite this underbrush and start an uncontrollable fire. Wildfires can move up to 14 miles per hour and can last for weeks, threatening to burn down thousands of homes.
After a wildfire, there are no plants or trees to anchor soil. This leads to land slides which can further endanger people and their homes. Despite the danger and negative consequences of wildfires, many ecosystems depend on occasional fires, which clear away dense brush and leave fertilized soil. One of the worst fires in North America was the Great Fire of 1910, which occurred in Idaho and Montana. Severe winds combined with dry forests contributed to the fire's ferocity. The fire lasted for two days, but it killed 86 people and destroyed 3 million acres of land. In the end, it prompted Congress to give money to the National Forest Service to fight future wildfires.