Podcast
Questions and Answers
Which geographical feature acted as a bottleneck for Ice Age floodwaters flowing towards the Pacific Ocean?
Which geographical feature acted as a bottleneck for Ice Age floodwaters flowing towards the Pacific Ocean?
What evidence suggests icebergs were present in Lake Lewis during the Ice Age floods?
What evidence suggests icebergs were present in Lake Lewis during the Ice Age floods?
Which geological features are results of the scouring action of the Ice Age floods?
Which geological features are results of the scouring action of the Ice Age floods?
The Columbia River Basalt Group is unusual because it:
The Columbia River Basalt Group is unusual because it:
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What caused the formation of the fissures that allowed the Columbia River Basalt Group to erupt?
What caused the formation of the fissures that allowed the Columbia River Basalt Group to erupt?
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What was the primary cause of the Missoula floods?
What was the primary cause of the Missoula floods?
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What is the significance of the banded deposits at the bottom of glacial Lake Missoula?
What is the significance of the banded deposits at the bottom of glacial Lake Missoula?
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How long ago did the Missoula Floods occur?
How long ago did the Missoula Floods occur?
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What technology is used to reveal the scars of past floods by measuring the distance with light pulses?
What technology is used to reveal the scars of past floods by measuring the distance with light pulses?
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What is measured by LIDAR technology to create terrain maps?
What is measured by LIDAR technology to create terrain maps?
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What major geological event is created the Channeled Scablands of Eastern Washington?
What major geological event is created the Channeled Scablands of Eastern Washington?
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What new findings have researchers uncovered about the sources of ancient flooding in the Channeled Scablands?
What new findings have researchers uncovered about the sources of ancient flooding in the Channeled Scablands?
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What is the purpose of studying the ancient geomorphology of the Channeled Scablands in relation to current environmental changes?
What is the purpose of studying the ancient geomorphology of the Channeled Scablands in relation to current environmental changes?
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Approximately how long ago did the last Cascadia subduction zone earthquake occur?
Approximately how long ago did the last Cascadia subduction zone earthquake occur?
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What is the approximate length of the Cascadia subduction zone fault?
What is the approximate length of the Cascadia subduction zone fault?
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In the context of earthquake preparedness, what is a practice that can be done without construction skills?
In the context of earthquake preparedness, what is a practice that can be done without construction skills?
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The Cascadia subduction zone has been building tension for how long?
The Cascadia subduction zone has been building tension for how long?
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What is the estimated likelihood of a major earthquake occurring in the Cascadia subduction zone within the next 50 years?
What is the estimated likelihood of a major earthquake occurring in the Cascadia subduction zone within the next 50 years?
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Why is the 2011 Japan earthquake relevant to the discussion about the Cascadia subduction zone?
Why is the 2011 Japan earthquake relevant to the discussion about the Cascadia subduction zone?
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What was a major factor in the high number of casualties following the 2011 Japan earthquake?
What was a major factor in the high number of casualties following the 2011 Japan earthquake?
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What is the primary recommendation authorities give for earthquake safety?
What is the primary recommendation authorities give for earthquake safety?
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Subduction zone earthquakes are characterized by what unique feature?
Subduction zone earthquakes are characterized by what unique feature?
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What makes magnitude nine earthquakes particularly destructive?
What makes magnitude nine earthquakes particularly destructive?
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What is a common characteristic of the Sumatra (2004), Tohoku (2011), and predicted Cascadia megathrust earthquakes?
What is a common characteristic of the Sumatra (2004), Tohoku (2011), and predicted Cascadia megathrust earthquakes?
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Which type of seismic wave is characterized as a pressure wave and travels fastest?
Which type of seismic wave is characterized as a pressure wave and travels fastest?
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What is the primary concern regarding wood-frame houses during an earthquake?
What is the primary concern regarding wood-frame houses during an earthquake?
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What does 'ductile' mean in the context of building materials and earthquake resistance?
What does 'ductile' mean in the context of building materials and earthquake resistance?
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In the context of earthquake safety, what is primarily meant by 'situational awareness'?
In the context of earthquake safety, what is primarily meant by 'situational awareness'?
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What was the original context for the 'drop, cover, and hold on' advice?
What was the original context for the 'drop, cover, and hold on' advice?
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What natural disaster can tsunamis commonly be caused by?
What natural disaster can tsunamis commonly be caused by?
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What effect does a tsunami have as it approaches the shore?
What effect does a tsunami have as it approaches the shore?
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Which factor is critical in determining survival during a tsunami event?
Which factor is critical in determining survival during a tsunami event?
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What is a crucial factor that impacts survival rates during a tsunami triggered by a local earthquake?
What is a crucial factor that impacts survival rates during a tsunami triggered by a local earthquake?
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How often do tsunami waves typically arrive after an initial wave?
How often do tsunami waves typically arrive after an initial wave?
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What did scientists discover about past earthquakes and tsunamis in the Cascadia region?
What did scientists discover about past earthquakes and tsunamis in the Cascadia region?
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Study Notes
Pacific Northwest Ice Age Floods
- Columbia River Basalt Group: A massive lava flow, exceeding two miles thick, erupted from fissures related to a tectonic hot spot under southeastern Oregon. This differs from most basalt eruptions, which occur in ocean basins. More than 300 eruptions, interspersed with periods of inactivity, occurred over 17.5 million years.
- Lava Flows: The low-silica, fluid-like lavas flowed across North America, burying landscapes and covering tens of thousands of square miles.
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Ice Age Floods: Enormous glacial meltwater floods, not lava, altered the landscape. These included the Missoula floods (from glacial Lake Missoula, Montana) and Bonneville flood (from Lake Bonneville, Utah).
- Missoula Floods: When glacial Lake Missoula's ice dam breached, water surged through Eastern Washington and into the Pacific Ocean at rates up to 10 cubic miles per hour, ten times the flow of all Earth's rivers combined. This occurred repeatedly, possibly over 100 times, leaving distinct layered sediments.
- Bonneville Flood: Lake Bonneville, a precursor to the Great Salt Lake, spilled from Utah, flooding Southern Idaho. The peak discharge was less intense than the Missoula floods, but the flood lasted longer, for weeks instead of days.
- Flood Features: The floods carved channels, canyons, and coulees (box-shaped valleys), forming dramatic landmarks like Grand Coulee and Dry Falls. They transported large boulders and formed piles along their paths.
- Sedimentary Deposits: Floods left sedimentary deposits (e.g., slack water sediments, erratics, glacial till, glacial outwash) throughout the region, revealing the extent and intensity of the events, even using LIDAR.
- Lake Lewis: Areas like Wallula Gap trapped floodwater, creating temporary reservoirs (Lake Lewis) that briefly slowed floodwaters.
- Lava and Flood Interactions: Lava flows interacted with floodwaters, sometimes forming pillow structures and petrified logs, offering hints about past environments between eruptions.
- Flood Impacts: The floods reshaped the Eastern Washington landscape, creating a desert-like terrain despite the immense water volumes.
- Evidence and Research: Geological mapping, analysis of erosion patterns, and study of sedimentary layers provide data on these events. LIDAR (light detection and ranging) technology allows for mapping the Earth's surface, visually revealing past river channels and flood features, including ripple marks and features previously hidden from view. Recent LIDAR research suggests floods originating from multiple sources, including the Okanagan Valley and sources north of the Channeled Scablands, not just glacial Lake Missoula.
- Additional Information: A 600-mile long fault line, the Cascadia subduction zone, runs from Northern California to British Columbia. It has produced 41 subduction zone quakes in the last 10,000 years, averaging one every 250 years. The most recent was in 1700. The Juan de Fuca plate is pushing under the North American plate, slowly building tension. A magnitude 9 earthquake along this fault is possible, and quite likely to occur within the next 50 years. Such an earthquake has a 37% chance of happening. Tsunamis are caused by displacement of the ocean floor, creating a massive wave. Tsunamis are not produced by wind like normal waves; they move large quantities of water and can travel over 500 miles per hour. They accelerate as they move towards shorelines. Coastal areas are vulnerable, and the 2004 Sumatra earthquake and tsunami, a magnitude 9.1, was the deadliest on record. The Cascadia megaquake, an earthquake along the Cascadia subduction zone, could trigger deadly tsunamis. Planning and preparation are essential in high-risk areas.
Cascadia subduction zone Earthquake information
- Earthquake Types: Subduction zone earthquakes are the most destructive. A magnitude 9 earthquake is possible, and likely, within the next 50 years, with a 37% chance of happening.
- Earthquake Warning Signs: Subduction zone earthquakes provide a warning – P-waves (pressure waves) travel faster than S-waves (damaging waves). The P-wave shaking is light but provides a critical warning time; the time between the P-waves and the larger shaking is vital near fault lines.
Earthquake Effects and safety
- Building Safety: Building construction significantly impacts survival. Buildings built since the mid-1990s or retrofitted are more resilient. Older unreinforced masonry buildings (URMs) are dangerous and more prone to collapse during strong shaking. Older buildings, particularly wood frame houses, are more flexible and less likely to collapse but are subject to damage from falling objects.
- Situational Awareness: Evaluating the evacuation factor versus drop, cover, and hold.
- Strategies: Drop, cover, and hold on is common advice, though not always the ideal choice. Situational awareness dictates the correct response: proximity to exits, nature of the building, and potential external dangers (liquefaction). Evacuation following P-waves might be safer than staying indoors in some situations in unreinforced buildings. Knowledge of high-ground and obstacles is essential for tsunamis.
- Building types Non-ductile or brittle buildings are often made of concrete, and are dangerous. Wood frame structures tend to be more flexible.
- Warning Time: P-waves give a warning time that is often critical in areas far from the faultline; this time can be used for deciding survival tactics and building evacuation.
- Tsunami Considerations: Tsunamis, generated by earthquakes, move at high speeds in deep water, but their speed decreases in shallower water, resulting in acceleration near shore. Tsunamis are not a single wave, but a series, and they can increase in size with each wave.
Location and Time
- Location: Pacific Northwest, specifically south of Lewiston, Idaho, and in cities like Portland and Seattle. Areas like Long Beach, WA, are particularly vulnerable.
- Time: Columbia River Basalt flows began 17.5 million years ago; Ice Age floods (Missoula and Bonneville) occurred within the past 17,000 to 20,000 years. LIDAR data uncover more details concerning the flooding history. Historic flood events, such as a 10-mile wide Colorado River flood in 1869, also provide context. A magnitude 9 earthquake along the Cascadia Subduction Zone is possible and quite likely to occur within the next 50 years, with a 37% chance. The last quake happened in 1700. Evidence of past tsunamis, like drowned forests, provides historical context.
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Description
Test your knowledge about Oregon geologic history, as well as regional earthquake and tsunami hazards.
