Understanding Natural Hazards

Earth processes are natural phenomena that pose risks to humans. These hazards include earthquakes, tsunamis, hurricanes, floods, droughts, landslides, volcanic eruptions, extreme weather, lightning-induced fires, sinkholes, coastal erosion, and comet and asteroid impacts, among others. But, can natural disasters serve a purpose in nature?

Natural hazards shape the history of human societies. Hazardous events can significantly alter the size of human populations and drive human migrations. Risks from natural hazards increase as populations expand into vulnerable areas or concentrate in already-inhabited areas.

An Earth-science-literate public is essential for reducing risks from natural hazards. This literacy leads to the promotion of community awareness about natural hazards and to the development of scientifically informed policies that reduce risk.

Science of Natural Disasters

Thanks to the scientific method, we now understand where and why most natural disasters occur. For example, because of the theory of plate tectonics, we understand why nearly 90 percent of all earthquakes and volcanoes on Earth occur along the Pacific Ocean’s outer edges, called the Ring of Fire. The theory of plate tectonics has also helped to explain why some volcanoes are more explosive and dangerous than others.

Internal and External Forces

In general, two types of forces generate natural hazards: internal forces and external forces. The internal forces arise with Earth, for example, the internal heat of the earth which is responsible for the movement of plates. The theory of plate tectonics proposes that internal heating from the earth’s core causes large tectonic plates that make up the planet’s continents and oceans and move around like bumper cars, where they either slam into each other or pull apart.  External forces come from the sun or the moon and influence weather and climate. For example, uneven heating from the Sun causes wind circulation around the atmosphere and different pressures, which can generate weather patterns and extreme weather events. The gravity between the moon and the earth causes tides. The interactions between these forces and the Earth’s spheres control most natural processes.

Natural hazards controlled by external forces (as opposed to the earth’s interior) have seasons. The United States has more tornadoes than the rest of the world combined, yet they most only occur in the spring and early fall. Landslides are more prone in the spring when the snow melts, and the saturated ground causes unstable slopes to slide. Wildfires are frequent in the middle of the summer and early fall when the land is dry, and afternoon thunderstorms in arid climates produce lightning with no precipitation. Hurricane season in the Northern Hemisphere peaks between August and September when the Atlantic Ocean is warmest.

Disaster Forecast, Prediction, and Warning

Humans cannot eliminate natural hazards but can reduce their impacts. We can reduce the loss of life, property damage, and economic costs by identifying high-risk locations and minimizing human habitation and societal activities in them, improving construction methods, developing warning systems, and recognizing how human behavior influences preparedness and response.This is the function of forecasting, predicting, and warning when a disaster is coming.

Another way in which we can reduce the impacts of disasters is by refining our knowledge about them. Earth scientists are continually improving estimates of when and where natural hazards occur. Since hazards are statistically predictable, it becomes essential to develop a warning system. Predictions, such as weather predictions, state that it will occur at a specified time, date, and intensity. It is like saying, “a major dust storm will reach Phoenix at 4:30 PM for the commute home.” A forecast states a probability of something occurring, such as “5 percent of showers today.” Forecasts are much broader than predictions.

When a natural disaster event is about to happen or has occurred, we have set a system up to alert the public. A watch is issued when the conditions for an event are right. If a severe thunderstorm is strong enough and it is rotating, a tornado may form. Alternatively, if an earthquake with a magnitude of 7.5 strikes somewhere in the ocean, a tsunami watch may be issued because it was strong enough to generate one. However, a watch does not necessarily mean that it will occur. A warning is sent out to the areas that could be impacted if a tornado is spotted on the ground or an ocean sensor records an approaching tsunami.

Determining Risk

To understand how to prepare for a natural hazard, scientists conduct a risk assessment for a specific geographic area. From an environmental perspective, we define the risk of a potential hazard as the probability of a disaster multiplied by the consequence to the human environment.

It is essential to determine the potential risk a location has for any particular disaster to know how to prepare for one. One of the limiting factors of risk is knowing the probability of a disaster. Too often, scientific data is lacking enough information to determine how often a disaster occurs for a particular location. This is true with geologic hazards, where geologic time is vastly more extensive than the age of scientific reasoning.

Hazards, Disasters, and Catastrophes

What is the difference between a natural hazard, a disaster, or a catastrophe? A hazard is any natural process, or even that poses a direct threat to the human environment. The event itself is not a hazard; instead, a process or event becomes a hazard when it threatens human interests. A disaster is the effect of a hazard on society, usually as an event that occurs over a limited time in a defined geographic area. We use the term disaster when the interaction between humans and a natural process results in significant property damage, injuries, or loss of life. Finally, a catastrophe is a massive disaster that significantly impacted the human environment and requiring a significant expenditure of time, money, and resources for response and recovery.

An article by NASA titled The Rising Costs of Natural Hazards talks about how the financial and human cost of natural disasters is rising. To help prepare for these disasters, better mitigation efforts will be required, such as proper building and zoning codes, first responder preparedness, and public education.

Are natural disasters getting worse? Not really. Humans are over-populating the earth and living in more hazard-prone areas. Over the last 70 years, the world’s population has tripled to 6.7 billion. World population projections suggest that the human population will reach 9 billion by 2050. by exponentially grow, and by 2050 the world’s population will reach 9 billion. Exponential growth means the world’s population will not grow linearly (in a straight line), but rather as a percent. Our increased population size has caused air quality to suffer, reduced the availability of clean drinking water, increased the world’s extreme poverty rate, and has made us more prone to natural hazards.

There is also a relationship between the magnitude of an event (energy released) and its frequency (intervals between episodes). The more earthquakes that occur for a particular location, the weaker they tend to be. That is because built-up energy is slowly being released at a relatively constant rate. However, if there are long intervals between one earthquake and the next, the energy can build and can ultimately produce a stronger earthquake. That is the problem with earthquakes along the Wasatch Front of Utah. The interval or frequency between earthquakes tends to be 1,500 years, so the magnitude tends to be high because of the built-up energy. At some point, we are going to want to get this earthquake over with because the longer it waits, the worse it will be.

Primary and Secondary Effects of Natural Disasters

​There are two types of effects caused by natural disasters: direct and indirect. Direct effects, also called primary effects, include destroyed infrastructure and buildings, injuries, separated families, and even death. Indirect, sometimes called secondary effects, are things like contaminated water, disease, and financial losses. In other words, indirect effects are things that happen after the disaster has occurred.

How we chose to build our cities will significantly determine how many lives are saved in a disaster. For example, we should not be building homes in areas that are prone to landslides, liquefaction, or flash floods. Instead, these places should be left as open-space such as parks, golf courses, or nature preserves. This is a matter of proper zoning laws which are controlled by the local government. Another way we can reduce the impact of natural disasters is by having evacuation routes, disaster preparedness and education, and building codes so that our building does not collapse on people.