Natural disasters and storm damages claim Oregon’s attention year-round, requiring robust preparedness measures. Residents and authorities continually work together to minimize risks and ensure communities remain resilient.
Oregon’s Department of Land Conservation and Development identifies the six most common natural hazards in the state. These are floods, landslides, earthquakes, tsunamis, coastal erosion and wildfires. In addition, Oregon also has volcanic hazards as well as experiences winter storms, windstorms, dust storms and droughts.
Let’s discuss the kind of disasters in more detail below.
Floods
Almost every year, Oregon experiences damaging floods. There are 251 flood-prone communities in the state, including locations in all 36 counties, 212 cities and three tribal nations, according to the National Flood Insurance Program (NFIP).
The typical types of flooding Oregon include river flooding, flash flooding, coastal flooding and floods brought about by tropical systems.
There is typically a risk of flooding after a heavy rainfall especially over a period of days. However, flash floods can also happen because of quickly rising water levels in areas along streams or other low-lying locations. The rushing waters of flash floods can carry rocks, mud and other debris as well as sweep away people, vehicles and most other things in its path.
Flooding due to dam breaks can be as devastating as flash floods. And, overland flooding can happen when a levee is breached. Dam breaks and levee failure can be caused by water overflowing from the structure, a structural failure, or excessive seepage of water in the surrounding ground.
Snowmelt can cause flooding in the spring. Water saturates nearby streams and rivers, which results in a quick rise in their water levels leading to an eventual overflow. Chunks of ice or a buildup of debris can also cause a blockade in rivers or streams and cause their waters to overflow into the surrounding areas.
Extremely dry land and burn scars from wildfires can also cause floods in Oregon. This happens because dry or bare soil repels water instead of absorbing it.
Landslides
Similar to floods, landslides are common in Oregon. Places near moderate to steep slopes are at risk, especially during intense or prolonged rainfall or rapid snow melt. Shocks or vibrations from earthquakes or construction also make sloping ground or areas near riverbanks prone to landslides.
Freeze-thaw cycles and volcanic eruptions can also trigger landslides in the state. Altering slopes, such as placing fill or weight on steep slopes or undercutting a slope or cliff by excavation or erosion, can also result in landslides. Removing vegetation, which holds the soil together, by land clearing, timber harvesting or fires can also lead to landslides in the area.
Landslides are natural processes where soil, rock or their combination move down the slope because of gravity. However, they can cause injuries to people, damage property and impact transportation and other public facilities.
Earthquakes
Oregon is one of areas in the continental United States that are most prone to earthquakes. The Beaver State experiences both small and large quakes. Small quakes are less than 3.0 magnitude, and they may occur often but not felt. Meanwhile, large earthquakes can be devastating, affect thousands of people and cause millions in damages.
Earthquakes in Oregon can come primarily from four sources.
- Cascadia Subduction Zone (CSZ)
The Cascadia Subduction Zone (CSZ) is a 600-mile fault that extends from Northern California to British Columbia, just 70-100 miles off the Pacific coast shoreline. Most quakes in the Pacific Northwest result from the subduction process, which happens when two tectonic plates converge, specifically, an oceanic plate moves under a continental plate.
This type of earthquake has the potential to reach 9.0 magnitude or higher and can last up to five minutes. If such a quake was to occur, it could create a series of tsunamis along the coast.
- Volcanic activity
The subduction process also formed the Cascade Range volcanoes. So, volcanic activity in this range can trigger earthquakes that can affect other areas.
- Crustal quakes
Earthquakes can also happen on faults, which are breaks in the crust. These crustal quakes occur above the subducting plate, within the North American plate, at shallow depths of 6-12 miles (12-20 km) below the surface.
- Intraplate earthquakes
Quakes can also occur deep within the subducting oceanic plate. We call these intraplate earthquakes, whose tremors can be felt very strongly near the epicenter. These types of quakes can be felt throughout Oregon.
Tsunamis
While tsunamis don’t occur frequently in Oregon, the series of long and high sea waves or surges that they bring can cause devastation to the state’s coastal areas and communities.
Tsunamis are most often caused by a volcanic eruption, a landslide or a large offshore quake. The no. 1 reason for a tsunami in Oregon is an earthquake, such as one from the Cascadia Subduction Zone, where the abrupt change in the seafloor can trigger a large wave. Earthquakes with 9+ magnitude can create tsunamis that will hit the coasts of Oregon as well as Washington and northern California.
Underwater volcanic eruptions can also trigger tsunamis in the area. So will landslides, whether they start above water or below the water surface.
There are two types of tsunamis: local and distant.
- Local tsunamis
Local tsunamis are triggered by sources immediately adjacent to the coast, and as such, the waves will only take minutes to reach the shore. For instance, a tsunami caused by a CSZ earthquake would only take 15-20 minutes to reach Oregon. Because they have only traveled a short distance, most local tsunamis feature high waves of 20-80 feet and can travel farther inland at 30 mph compared to distant tsunamis. The height of the wave and its speed will depend on the amount of fault movement, the shape of the shore and the local water depths or coastal bathymetry.
- Distant tsunamis
On the other hand, distant tsunamis are triggered by sources across the ocean basin, usually by a subduction zone earthquake in the Pacific, so the waves will take some time, typically several hours, to reach the coast. The closest source is the subduction zone in the Gulf of Alaska, and a tsunami from this source will take at least 4 hours to reach the shores of Oregon. This is exactly what happened in 1964, when a tsunami from Alaska took 4-5 hours before reaching the state.
Coastal Erosion
The coasts of Oregon, as with other places, are dynamic. Sands can shift and change the environment in an instant, so any permanent infrastructure can quickly become devastated by natural processes.
When it comes to coastal erosion, Oregon’s coastal communities experiences the following:
- Beach or dune erosion
Beaches and sand dunes are a coastal community’s first line of defense against powerful ocean waves. They are dissipated by beaches and sand dunes so that land features are preserved.
However, sand is constantly shifted by the waves, currents and the wind. In the state, major erosion of beaches and sand dunes result from a combination of storm surges, high tides, strong nearshore currents and intense waves.
The worst on record is the winter of 1939, which saw coast-wide erosion. Recently, increased erosion of beaches and sand dunes, as well as the migration of river inlets, have been attributed to El Niño winters.
- Bluff erosion
Unlike beaches and sand dunes, bluffs see long-term erosion, thanks to the constant battering of the waves and the effect of the weather. Other factors that affect the erosion of bluffs include vegetation cover, bluff material properties and bluff slope. Bluffs can be so deformed that they are at risk of landslides. The erosion of bluffs is responsible for the largest loss of property values, according to the Oregon Department of Geology and Mineral Industries.
Wildfires
Wildfires in Oregon are a common occurrence, especially during the summer and fall. These months provide a dry climate, ample fuel and combustion from man or lightning. About 70% of fires in the last decade are caused by man, but in terms of acres burned, around 80% are due to lightning-ignited blazes.
The Oregon Natural Hazards Mitigation Plan (2015) calculated about 240,000 houses are in the Wildland-Urban Interface, which means they have a higher risk of wildfires.
What kind of disasters happen in Oregon?
In conclusion, Oregon faces a variety of natural disasters, necessitating solid preparedness and community resilience to minimize the extensive risks involved.