Hurricanes are also known as cyclones or typhoons, depending on the area of the world. Meteorologists normally refer to them as tropical cyclones. Hurricanes consist of an area of calm at the core, know as the eye of the storm, surrounded by a swirling, fast-moving vortex of wind and rain storms. Hurricanes occur when groups of thunderstorms drift over warm oceans. The warm air from the storm and air at the surface of the ocean begin to rise. As the air rises, it creates an area of low pressure at the surface of the ocean. Trade winds blowing from different directions cause the storm to start spinning. As the warm air continues to rise, it causes the areas of low pressure to get higher and higher. The air rises faster and faster, pulling in cooler air downwards towards the ocean. The storm moves across the ocean this process continues to happen and the wind speeds increase. If luck is on your side the hurricane dies before it reaches land but when it doesn’t they can be very destructive. The deadliest tropical cyclone was the 1970 Bhola Cyclone that killed up to 500,000 people in modern day Bangladesh. It had peak winds of 185 km/h (115 mph), some of the highest ever recorded during a tropical cyclone.
Tornadoes, like hurricanes, are also known for high wind speed and destruction. Tornadoes are also known as twisters, whirlwinds, or cyclones. They are a funnel of rapidly moving air that are in contact with the surface of the earth. They occur when humid air is heated and starts to rise. As this moist air meets cold air, it can form thunder clouds. This can cause a thunderstorm. The upward movement of air combined with winds from other directions can cause the air to rotate, sometimes causing the visible ‘twister’ funnel form out of the bottom of the cloud. They can last a just a few seconds or it can be up to over an hour before they dissipate. The fastest wind speed ever recorded from a tornado (and the fastest wind speed ever recorded) was the Bridge Creek-Moore tornado in 1999 where wind speeds of 484 km/h (300 mph) were measured. The United States, on average, has the most tornadoes each year, but they can be found all over the world. In the US, they are mostly found in the great plains, colloquially known as Tornado Alley.
The Earth’s crust is broken up into pieces known as tectonic plates. These plates sit on a semi-molten layer called the mantle. Uneven heating in the mantle causes convection currents which cause the tectonic plates to move. These tectonic plates don’t always move with each other smoothly. Earthquakes are caused by sudden jolts in tectonic plates. Thousands of earthquakes happen every day, but most of them are too small for humans to notice and they are only detected by a sensitive scientific instrument known as a seismometer. When they are large enough, earthquakes can destroy whole cities, but they mainly occur around fault lines. The largest Earthquake ever recorded happened on May 22, 1960 in Valdivia, Chile. It measured 9.5 on the moment magnitude scale. Between 1,000 and 6,000 people lost their lives. The quake triggered landslides in the valleys of the Andes and a huge Tsunami which traveled westward across the Pacific Ocean and caused loss of life in Hawaii. Find more content in the lesson plans for the Structure of the Earth and Plate Tectonics.
Tsunamis can occur from earthquakes, volcanic eruptions, or explosions under the ocean. The seismic waves can jolt the seabed, which can displace huge amounts of water in the ocean. This causes large waves to spread from the epicenter. In deep water, the waves move quickly; when they reach shallow coastal areas, they slow down but their height increases. These waves could cause huge destruction when they reach land.
An avalanche occurs when a large amount of snow and ice slides down a slope rapidly. This can be caused as snow and ice starts to build up and there are weaker layers underneath. The dangers are the fast moving snow will bury whatever or whoever is in its path. Sometimes small avalanches are triggered on purpose in a controlled way to make some mountainous areas safer. They do this when the build up of snow is small so as not to cause damage or injury.
Most volcanoes are very safe. They only really become dangerous during a volcanic eruption. There are hundreds of potentially active volcanoes around the world, most of which are found along the fault lines of the earth. At some boundaries between tectonic plates, magma can rise up and find its way to the upper crust. The molten rock is known as magma when it is under the earth, and lava when it reaches the surface. If it can reach the surface it is known as a volcano. After successive eruptions, the lava cools and forms the cone shape of a volcano. Volcanoes erupt when the pressure of the magma below in the magma chamber is so great, it can break through the rock at the top of the volcano. As the volcano erupts large rocks are thrown into the air along with a hot cloud of rock and ash. This cloud of ash, known as a pyroclastic flow, moves quickly like an avalanche and can engulf everything in its path. The worst volcanic eruption in history was the 1815 eruption of Tambora, Indonesia that killed around 90,000 people.
A heatwave is a period of excessively high temperatures, often with high humidity. High temperatures can have negative effects on people’s health and can even cause death. Heatwaves can also cause mass power outages as many people turn up their air conditioning.
A drought is characterized when the rainfall in an area is less than average to the point where there is a negative effect on the water supply. This can have a large impact on agriculture as crops cannot grow without water. This can potentially lead to famine as farmers can’t produce enough food for everyone. A lack of water can lead to mass migration of people and animals as they go in search of areas with more water.
Landslides, also known as landslips, can vary massively in their size and destruction, but they always involve the movement of land. Landslides occur when the ground on a slope becomes less stable. This could happen due to a number of reasons including erosion, groundwater flow, and deforestation. The triggers for landslide including any seismic activity from earthquakes or volcanoes, or vibrations from heavy machinery. They have the potential for a large amount of damage and loss of life if residential areas are in the path of the flow of land.
Wildfires or forest fires can be started by natural causes, such as lightning, but also by humans. Sometimes humans start them intentionally to clear brush, but also wildfires start accidentally. Wildfires have been caused by cigarettes, grills that haven’t been extinguished properly, and campfires that haven’t been managed properly. They can be extremely difficult to stop once they have started and can destroy large areas of forestland. Often firefighters will use ‘waterbombers’, or aircraft that can spray water from the air over large areas of forest.
Blizzards are a type of dangerous snowstorm where there are powerful winds with a minimum speed of 56 kph (35 mph). These storms typically last a number of hours and results in low visibility, making driving very dangerous. There is a danger to life as blizzards are associated with very low temperatures and snowdrifts which can shut down whole towns and cities.
Floods can occur for a number of different reasons at many times throughout the year. Simply put, a flood is when land is covered by water when it normally isn’t covered by water. This can occur whenever there is a large amount of precipitation or melting ice that causes a lake, river, or ponds to overflow. Often with heavy rain the rivers and natural drainage cannot cope with the rate of water flow. The moving water can cause debris to block drains making it even more difficult for the water to more freely. Floods can cause extensive damage to property and can also cause loss of life. The worst flood ever recorded happened in China in 1937 where between one million and four million people died.
Essential Questions for Natural Disasters
- What is a natural disaster?
- What are examples of different natural disasters?
- Why do natural disasters occur?
- What can we do to prevent/survive a natural disaster?
Other Lesson Plan Ideas for Natural Disasters
- Create a T-Chart to compare the causes and effects of two different natural disasters.
- Create a Richter scale (or moment magnitude scale) showing the effects of different magnitudes of earthquakes.
- Create a timeline showing advances in technology which helps protect us from injury during a particular natural disaster.