We're familiar with many natural disasters as they often make headline news: earthquakes, volcano eruptions, tsunamis, hurricanes, blizzards, floods, and droughts are all examples. We call them "natural disasters" because they are events that occur outside of human control and they often have damaging or destructive effects to human structures, human lives, or food supplies. The destructive potential these events present to our familiar surroundings is what makes us dislike and fear them, and it's difficult or impossible to prepare for these events in advance.
Why do these disasters happen?
To state it simply: because we reside on a living planet — one that is constantly in a cycle of renewing itself. In most cases, this renewal involves barely perceptible events that recycle all the matter and energy on the Earth's surface — like erosion, chemical weathering of rocks, photosynthesis, or organic decomposition. However in some cases, this renewal and change can occur suddenly and violently — and when humans and the collection of stuff we call "home" get in the way, there can be disastrous consequences.
To break it down, we can think of the Earth as one big system, made up of four major subsystems or 'spheres that interact with each other, and undergo different processes of renewal.
Did you know?
There are four major subsystems on Earth — the Lithosphere, Hydrosphere, Atmosphere and Biosphere.
The Lithosphere , or solid Earth, is composed of all the rocks beneath our feet. The Earth has a solid core, surrounded by a viscous (thick and gooey) molten layer called the mantle , and a thin rocky shell called the crust . The crust is made up of a bunch of pieces called continental plates , which fit together like puzzle pieces and float over the mantle.
At some of the plate boundaries, new material from the mantle rises to the surface, and spreads outwards, while at other boundaries, one plate is pushed under the other, causing old material to return to the mantle. You can think of this as a massive recycling system for all the materials on the planets surface!
Did you know?
These movements happen very slowly, but occasionally there are violent releases of strain or pressure near the boundaries of these plates — and we know these as earthquakes and volcanoes.
The Hydrosphere is all the water on Earth including the oceans, lakes, rivers, ice, ground water, and water vapor in the air. It might not seem like it, but water is always on the move, being evaporated, precipitated, and transported between these different reservoirs. In transit, it can do some powerful things: floods can cover cities, raging rivers can wash out bridges and roads, and ice storms can break power lines and other structures.
The Atmosphere is everything in the air around us, from the surface of the Earth to the boundary of space, about 100km up. The atmosphere is composed of Nitrogen, Oxygen, Carbon Dioxide, water vapor and several other gasses. These gasses absorb a lot of energy from the sun, so it's very energetic and active. Different parts of the atmosphere receive more energy from the sun than others (think day vs. night, or cloudy sky vs. clear sky) keeping the atmosphere in a tumultuous state of energy unbalance. Since energy is always trying to find a state of balance (energy flows from areas of high concentration, to low concentration) we get parcels of air moving chaotically through the atmosphere: wind!
Did you know?
The hydrosphere and atmosphere interact to produce our weather and climate. The cycles of evaporation and precipitation, combined with wind, are why we experience rain and snow. Really extreme events, where a lot of energy is moving around, produce our big storms: blizzards, flash floods, and hurricanes. Too little or too much precipitation produces droughts or floods.
The Biosphere is everything living (including us!) on the Earth. Plants, animals, bacteria, and other life forms interact with the other Earth systems, exchanging water, minerals and gasses. Sometimes these interactions turn disastrous, such as when dry forests are set on fire by lightning strikes, or adverse weather causes food crops to fail.
It might be hard to accept, but "natural disaster" is just a term we use to describe something bad that's happened to us humans, during the daily business of a living planet!
- Natural Disasters (National Geographic.com) Learn more about different kinds of natural disasters, and see some great photography too!
- Natural Disasters (Wikipedia)
- Weather on Mars (NASA) What kind of Natural Disasters would explorers have to watch out for there?
- Kump, L. R., Crane, R.G., Kasting, J.F. (2004). The Earth System , Prentice Hall.
- Press, F. and R. Siever (2001). Understanding Earth . New York, W.H. Freeman and Company.