READ: Natural Hazards
READ: Natural Hazards
Explore this Phenomenon
These are photos of the California Memorial Stadium at the University of California, Berkeley.
- What are your observations about what has happened in these photos?
- What questions do you have about what has happened here?
- How do you explain what is happening?
The Hayward Fault passes directly beneath both end zones at California Memorial Stadium, the home of football at the University of California, Berkeley. The site probably looked flat and easy to build on in 1922 before knowledge of earthquake faults was very advanced. Scientists now know that the Hayward Fault shifted in 1868. Since the fault moves every 140 years on average, East Bay residents and geologists are working to prepare for the inevitable event. To make the stadium safe for workers, players, and fans, the stadium is being renovated in a $321 million project involving 10 miles of steel cables, silicone fluid-filled shock absorbers, concrete piers, 3 feet of sand, plastic sheeting, and stone columns.
Natural Hazards
We live on a planet that is constantly changing. These changes can lead to problems for the humans who live here. The rocks we stand on provide a solid surface for our buildings and roads. They seem steady but over time they slowly shift and move. The atmosphere we breathe allows us to live but the constant cycling of air and water sometimes releases more force that we would like, causing damage to lives and structures.
A natural hazard is an event that occurs in nature that has the potential to cause harm to humans or their property. Events that are a result of the geology of an area, for example earthquakes, volcanoes, landslides, rockfalls, or sinkholes are examples of natural hazards. Also included are hazards that are a result of atmospheric phenomena such as tornadoes, hurricanes, flooding, avalanches, blizzards, or windstorms.
Tornadoes such as the one in the photo happen most often in areas with frequent thunderstorms and flat land.
Strong tornadoes can level entire neighborhoods.
Mount St. Helens is a volcano in Washington state that erupted in 1980. Over 230 square miles were covered in debris from the volcano.
Lava flows like these in Hawaii often cover land that has been used by humans for homes and roads.
Steep slopes and cliffs often fail, causing mud, rocks and debris to fill valleys and cover homes and roads.
Predicting Natural Hazards
Sometimes we can predict when natural hazards will happen. Volcanic eruptions are often preceded by small earthquake swarms on the volcano. By mapping tornadoes and hurricanes we have realized that there are patterns in their occurrences. Some things are generally present when they occur. Tornadoes happen when a mass of cold air collides with a mass of warm air. Hurricanes form over oceans in the warm, moist tropics and then move northward with the prevailing winds. Landslides and rockfalls happen on steep, unstable slopes, usually when there is a lot of water present.
Some natural hazards, like earthquakes, are nearly impossible to predict. This is a very real problem for Utah. Utah is crossed by many active faults and earthquakes happen daily in Utah. Most are too small to feel though many of these faults are capable of very large earthquakes.
A Good Prediction
Scientists are a long way from being able to predict earthquakes. To be useful, a good prediction must be detailed and accurate. Where will the earthquake occur? When will it occur? What will be the magnitude of the quake? Currently scientists are not able to answer these questions in regards to earthquakes.
Detailed and accurate predictions can be very useful. With a good prediction authorities could get people to evacuate. An unnecessary evacuation is expensive and causes people not to believe authorities the next time an evacuation is ordered.
Where?
The probabilities of earthquakes striking along various faults in the San Francisco area between 2003 (when the work was done) and 2032.
Where an earthquake will occur is the easiest feature to predict. Earthquakes tend to happen where they’ve occurred before. (See figure.) Scientists know that earthquakes take place at plate boundaries or along major faults in the interior of continents, like the Wasatch Fault.
When?
When an earthquake will occur is much more difficult to predict. Since stress on a fault builds up at the same rate over time, earthquakes should occur at regular intervals. (See figure.) But so far scientists cannot predict when quakes will occur, even to within a few years.
Around Parkfield, California, an earthquake of magnitude 6.0 or higher occurs about every 22 years. So seismologists predicted that one would strike in 1993, but that quake came in 2004 - 11 years late.
Earthquake Signs
Occasionally we can guess that an earthquake is coming because there are signs that sometimes occur before a large earthquake. For example, small quakes, called foreshocks, sometimes occur a few seconds to a few weeks before a major quake. However, many earthquakes do not have foreshocks, and small earthquakes are not necessarily followed by a large earthquake.
Earthquake prediction is very difficult and not very successful, but scientists are looking for a variety of clues in a variety of locations in an effort to advance knowledge and improve the ability to predict earthquake location, timing, and magnitude.
Preventing Natural Hazards from Becoming Natural Disasters
Whether we can predict when disasters will happen or not, there are ways we can prepare for them in areas where they are likely to occur so that we can reduce their negative effects on society.
Scientists are developing technologies that will help us predict catastrophic natural disasters and mitigate their effects.
Caption: A seismograph is used to measure earthquake activity. Seismometers help us measure the strength of an earthquake while it is happening. They cannot predict an earthquake but by collecting information on earthquakes over time scientists can learn where earthquakes are more likely to happen.
Satellite images can include visual images, infrared heat images or a combination like the images above to track severe weather like hurricanes or ash from volcanic eruptions.
This is a radar image of a line of thunderstorms. Doppler radar bounces radio waves off objects like clouds to determine their location, movement, and intensity.
Many communities that are at risk for natural hazards put warning systems in place to communicate to their residents when a disaster is coming. These can be broadcasted over television, radio and now cell phones, or using sirens like these.
Tsunami buoys are placed far out in oceans to measure ocean waves. When they detect a tsunami approaching they send a warning signal to coastal areas.
Avalanche control. When snow builds up on mountain ridges and is at risk of falling and becoming an avalanche, technicians will clear the area of people and blast the snow with small explosions to trigger avalanches intentionally.
In areas where earthquakes are likely, buildings are now designed with features that will help them withstand the earthquake.
- Skyscrapers and other large structures built on soft ground must be anchored to bedrock, even if it lies hundreds of meters below the ground surface. They are also built to sway with an earthquake wave.
- The correct building materials must be used. Houses should bend and sway. Wood and steel are better than brick, stone, and adobe, which are brittle and will break.
- Large buildings can be placed on rollers so that they move with the ground.
- In a multi-story building, the first story must be well supported.
- Old buildings may be retrofitted to reinforce their structures.
The first floor of this San Francisco building is collapsing after the 1989 Loma Prieta earthquake.
Cost Considerations
Why aren’t all structures in zones at risk for natural disasters constructed for maximum safety? Cost, of course. More sturdy structures are much more expensive to build. So communities must weigh how great the hazard is, what different building strategies cost, and make an informed decision.
Putting It All Together
- How has your understanding changed?
- Can you think of another phenomenon that applies these concepts?.
- Explain what is going on based on what you have learned in this section.
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