This post first was published at my other blog.
10. Gravity currents
Yes, gravity is the culprit when you fall off a cliff but let’s not forget its effect on things around us. It can cause gravity currents, which work a little like lava lamps, but are much more deadly.
The “lava” sitting on the lamp bottom is heavier (more dense) than the water. As the lamp heats up, this “lava” expands, becoming lighter (less dense), and it rises.
In the real world, you just need density or temperature differences in the same material. That’s what goes on in powder-snow avalanches and volcanic pyroclastic flows. Since cold air is denser than warm air, a gravity current can also rush down during a storm as a microburst. These things move fast. A loose snow avalanche, for instance, can whip along at close to 200 mph (300 km/hr).
Landslides happen in many ways, even when the slope isn’t very steep. Sometimes the ground creeps down. Sometimes it comes down in a terrible rush, as in the Oso, Washington, landslide recently.
Slides happen regularly around the world. According to the Catholic University of Leuven’s OFDA/CRED International Disaster Database (EM-DAT), landslides killed 3,931 people between 2010 and 2013.
The most damaging ones worldwide happen when water is involved (either ground saturation or flooding after a slide blocks water flow); because of earthquakes; or during volcanic activity.
Massive tsunamis in 2004 and 2011 taught us to beware when water recedes quickly from a beach, whether or not we’ve felt the ground shaking. That’s good to remember, because tsunamis are also triggered by landslides.
In 1929, an underwater landslide caused a tsunami up to almost 90 feet (27 meters) high in Newfoundland. The biggest tsunami ever recorded was 1,720 feet high and ran 3,600 feet inland from Lituya Bay, Alaska. It happened in 1958 when a nearby magnitude 8 earthquake triggered a landslide into the bay.
EM-DAT records show that 20,387 people died in tsunamis between 2010 and 2013, including victims of the great March 2011 earthquake in Japan.
7. Ground Collapse
Ever have a nightmare about falling into a deep pit? Unfortunately, it sometimes happens in real life. For example, a Florida man died when a sinkhole opened up under his bedroom one night in March 2013.
Subsidence, compaction or collapse all cause drops in the ground level. Subsidence and compaction happen slowly, but there can be a sudden collapse if the roof of a mine or cave gives way.
You can ask local geologists if there are mines in your area, but it’s not always easy to know where sinkholes will form. They’re usually found in karst terrain where surface rock easily dissolves in groundwater. The water carves out a cave, and then its roof gives way.
Things happened a little differently in 2010 when a sinkhole in Guatemala City swallowed a three-story factory, causing multiple fatalities. The ground there is made of fairly loose volcanic pumice, and a geologist believes that water from leaking pipes, not groundwater or storm runoff, scoured out the 60 x 100-foot-wide crater.
Oddly enough, you’re more likely to drown in a desert than die of thirst. Flash flooding is the culprit. It happens there because hard desert soil doesn’t absorb much water. Runoff from slow-moving mountain storms rushes down otherwise dry riverbeds. Anybody in their path doesn’t stand a chance.
General flooding turns lethal when people underestimate the depth or power of water in a flooded area.
Drivers are especially at risk. Six inches of water can stall a car, and knee-deep water will float it.
Together, EM-DAT figures show, flash floods and general flooding killed 26,191 people between 2010 and 2013.
5. Severe weather
Water, ice, land and the biosphere constantly interact around us, powered by incoming energy from the Sun.
Windborne debris is the killer in tornadoes, cyclones and other storms, all of which additionally produce deadly lightning and enough water to drown in.
Excerpts of video surveillance footage of an F5 tornado destroying the First State Bank in Parkersburg, Iowa:
Temperature matters, too. Only a few degrees either way during a heat wave or cold snap can endanger your life. Left untreated, heat stroke causes brain and organ damage in a matter of hours, eventually leading to death. When it’s cold, hypothermia leads to heart and respiratory failure if you don’t get warm quickly.
Severe weather killed 68,549 people between 2010 and 2013.
Plague isn’t the world-changer it once was, but local outbreaks still happen in various parts of the world. It and other diseases killed 15,650 people worldwide from 2010 to 2013.
Cholera, measles, meningitis, polio, yellow fever and diarrhea all contributed to that toll. Vaccines can deal with those diseases, but not with the other two killers: dengue and Ebola virus.
Dengue is a mosquito-borne tropical virus. It comes in four varieties and usually hits you like a severe, flu-like illness. However, severe dengue can kill you within 48 hours without prompt medical care.
Ebola virus disease, a hemorrhagic fever, kills up to 90% of the people who get it, usually from shock. There’s no treatment for it, but intensive care and rehydration improve chances for survival. This nasty disease is transmitted by direct contact with body fluids or tissues of infected people or animals (particularly fruit bats, monkeys and gorillas in remote central and west Africa).
Bacteria and viruses aren’t the only quick-killing biological hazard out there.
3. Natural toxins
Wild and garden plants may contain cyanide. Other quick-acting toxins could be the plant’s essential oils (pennyroyal), tropane alkaloids (nightshade), amino acids (indigo) or lectin proteins (raw red kidney beans). Let’s not forget mushrooms—about 15-20 species worldwide are potentially lethal.
The United States Armed Forces Pest Management Board has a Living Hazards Database online of more than 500 venomous species worldwide. If images of snakes and insects disturb you, don’t visit its website. The list also includes (PDF) water creatures like the cone-shell snail (called most dangerous gastropod to humans) and Australia’s blue-ringed octopus.
After the initial shock, small primary ground waves that don’t do much damage are the first to arrive. Next come secondary ground waves that are larger and more destructive. Two kinds of surface seismic waves get mixed in, too: Rayleigh waves make the ground roll and Love waves move it sideways.
What happens next depends on where you are, what sort of material you’re standing on and whether it’s up to seismic code, and, of course, how powerful the earthquake is. In Seattle, for instance, some buildings could experience a sideways force of almost twice the pull of gravity during a major earthquake.
Throughout the world, 228,452 people died from earthquake shaking effects between 2010 and 2013.
Volcanoes reach out and touch you in most of the ways listed above.
These flashy killers cause earthquakes, landslides and mudflows. Searing pyroclastic flows race down their slopes. Deep fissures gape open, releasing lava and hot gas. Lightning flickers in massive ash plumes, while solid rock and lava bombs rain down on areas near the vent.
Icelanders also have to deal with sudden floods called jökulhlaups that occur when water, melted by heat from a volcanic vent, bursts out from underneath a glacier. Tsunamis from volcanic activity are rare but can be major disasters. Waves from Krakatoa’s 1883 eruption were up to 131 feet (40 meters) feet high and killed over 36,000 people.
Volcanoes also are armed with toxic gas. Of the three most hazardous volcanic gases, you can smell sulfur dioxide and hydrogen sulfide. Carbon dioxide is invisible and odorless. Heavier than air, CO2 flows along the ground, collecting in low areas.
The sulfurous gases irritate your skin and respiratory tract, but CO2 will kill you.
How deadly is carbon dioxide? In 1986, a cloud of it suddenly burst out of a crater lake in the Oku Volcanic Field of western Africa, killing more than 1700 villagers and their livestock, as well as wildlife within 15 miles (25 km) of the lake. Scientists later figured out that the deep lake’s bottom waters had absorbed a lot of CO2 from the volcano over time. Everything was okay until heavy rain upset the delicate internal balance and it overturned, releasing all the gas at once.