Unit 9 · Segment 4: Sustaining Living Systems in a Changing World · printed p. 326 (PDF p. 362)
Earth's Natural Hazards
Bridges in some places risk damage or destruction from multiple natural hazards including flooding, mass wasting, earthquakes, and even volcanic activity.
Anchoring phenomenon
Chapters
- 25 Volcanic Eruptions and Earthquakes
How can people forecast and prepare for volcanic eruptions and earthquakes when only one of them usually gives warning signs?
1 presentation10 worksheets3 labs - 26 Mass Wasting, Tsunamis, and Floods
How do scientists use patterns in data to forecast where and when mass wasting, tsunamis and floods are likely, and how do those forecasts shape the technologies and plans people use to reduce the harm?
1 presentation10 worksheets3 labs
Standards in this unit
Unit vocabulary
natural hazardA natural event, such as an earthquake, a volcanic eruption, a landslide or a flood, that can hurt people or damage what they have built. It becomes a disaster only where people, homes or roads are in its path.Chapter 25
magmaMolten or partly molten rock, carrying dissolved gases and crystals, below Earth's surface. Once it reaches the surface, it is called lava.Chapter 25
hot spotA place where an unusually hot plume of mostly solid rock rises from deep in the mantle and partly melts as the pressure on it drops, feeding volcanoes that can sit far from any plate boundary.Chapter 25
pyroclastic flowA ground-hugging avalanche of hot gas, ash and rock fragments that races down a volcano during an explosive eruption, often faster than 80 km per hour.Chapter 25
precursor eventA smaller, measurable change that often comes before a larger event. Before eruptions, precursors include swarms of small earthquakes, extra volcanic gas and swelling ground.Chapter 25
forecastA scientific estimate of how likely an event is in a given area over a given time span. A prediction would name the specific time, place and size, which nobody can do for earthquakes.Chapter 25
frequencyHow often an event happens during a set amount of time.Chapter 25
magnitudeA number for the size of an earthquake at its source, calculated from seismic wave recordings. The scale is logarithmic: each step of 1 means 10 times more ground motion on a seismogram and about 32 times more energy released.Chapter 25
focusThe place underground where rock first slips and an earthquake begins. Seismologists also call it the hypocenter.Chapter 25
epicenterThe point on Earth's surface directly above an earthquake's focus.Chapter 25
seismic waveA wave of vibration that carries energy away from an earthquake through rock. Body waves (P and S waves) travel through Earth's interior; slower surface waves travel along the surface and make it roll and sway.Chapter 25
mitigateTo lessen the harm a hazard causes, for example by keeping buildings off the most dangerous ground, building stronger structures, monitoring and planning evacuations. Mitigation does not stop the hazard itself.Chapter 25
mass wastingAny downhill movement of soil, rock or other earth material that gravity drives, whether it takes years or seconds.Chapter 26
creepMass wasting too slow to watch, often a few millimeters to a few centimeters a year, noticed through clues such as tilted fence posts, cracked walls and trees with curved trunks.Chapter 26
landslideA general name for a mass of rock, soil or debris that breaks loose and moves down a slope; many scientists use it for every kind of slope movement.Chapter 26
debris flowA fast, water-soaked slurry of mud, sand, boulders and often trees that pours down a channel like wet concrete. A mudflow is a debris flow made mostly of fine particles.Chapter 26
saturatedHolding as much water as the spaces between its grains can take. In saturated soil the water pressure lightens the grip between grains and the soil gets heavier, so slopes fail more easily.Chapter 26
tsunamiA series of very long ocean waves made when a large volume of water is suddenly pushed up or down, most often by an undersea earthquake. Tides and wind do not cause tsunamis.Chapter 26
DART systemNOAA's network of deep-ocean tsunami stations. A pressure sensor on the seafloor sends its readings by sound to a surface buoy, which relays them by satellite to warning centers.Chapter 26
runoffWater from rain or melting snow that flows over the land surface instead of soaking in, collecting in gullies, streams and low places.Chapter 26
storm surgeA rise of the sea above the normal tide caused mainly by a storm's winds pushing water toward shore, with a smaller boost from the storm's low air pressure.Chapter 26
atmospheric riverA long, narrow band of air carrying a large amount of water vapor, often from the tropics. When it reaches mountains the air rises and cools, and it can drop days of heavy rain and snow.Chapter 26
mitigationAction that reduces the harm a hazard can do, such as walls, drains, warning systems, building rules and evacuation plans. Mitigation lowers risk but cannot remove it.Chapter 26
scourErosion of a streambed or bank by fast-moving water around a bridge pier or abutment, which can undermine the bridge's foundation.Chapter 26