1. Catastrophic Events

2. Cause and Effect of Catastrophes
Wildfires
Wildfires are often caused either by lightning or human activities such as campfires and burning cigarettes, as well as arsonists. The severity of wildfires greatly depends upon the moisture, temperature, type of topography, and wind as well as the type and amount of fuel on the forest floor. Wildfires need oxygen and fuel to sustain the life of the fire. Wildfires can produce their own winds that can be ten times stronger than the winds around them.
If not controlled, a wildfire can burn through millions of acres of forest. Wildfires can destroy the protection of watersheds and animal life and cause economic losses. A benefit of wildfires may be an increase in the nutrients of soil (which causes new plant growth to come back quickly) and over time, new animal life.
Wildfires are a fundamental process that may have positive or negative consequences in an ecosystem. Fire can be beneficial for maintaining balance in an ecosystem as long as they are properly managed and controlled. Wildfires affect the air quality, water quality, soil composition, vegetation, and wildlife in ecosystems.
Hurricanes
Hurricanes are developed over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico each year. They start out as tropical storms (tropical cyclones). Hurricanes are created by moist, warm

3. air above the ocean that rises and cools forming clouds
air above the ocean that rises and cools forming clouds. Convection currents are developed when warm and cool air masses join together. The convection current causes the warm air to begin to spiral upward causing wind. As the winds reach a constant speed of 74 mph or more, the tropical storm is then upgraded to a hurricane. Hurricane winds blow in a spiral around a calm center called an eye. The eye can be up to 30 miles wide, and the storm can be 400 miles in diameter. Hurricanes can last a week or more while over water and travel the length of the East Coast of the U.S. This catastrophic event can have extreme torrential rains, extreme high winds, and a dangerous storm surge as it approaches land.
Most deaths from hurricanes are due to flooding. Winds can drive ocean water up the mouth of rivers. Flooding can trigger mudslides or landslides. Tornadoes can be spawned by hurricanes. Economic costs and habitat loss is common.
Hurricanes may have several major negative impacts on the structure and function of ecosystems, such as uprooting trees, destroying animal life, and destroying habitats as well as completely stripping vegetation.
Droughts
A drought is the lack of moisture in a particular area for an extended period of time. A drought is an unusually long period of dry weather that causes water supply shortages. The severity of the drought depends upon the following: moisture deficiency, duration, and size of the affected area. Droughts last for two to three years and may cause serious problems such as the lack of water supply for humans and plants. Some areas can become desert when a drought occurs. Other Grade 7 Science Unit: 04 Lesson: 01
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related problems include crop failure, livestock death, increased forest fires, energy production, and water shortages.
Droughts may have major impacts on the environment. The increased amount of heat waves can add stress to ecosystems. This heat causes high temperatures, dry soils, or high evaporative demands upon the environment.

4. VolcaA volcano is an opening in the Earth’s crust which allows molten rock (magma) to escape out. Eruptions occur as a result of increased pressure from gases within the magma. When the volcano erupts the pressure from gases are released, moving the Earth to a state of equilibrium. Volcanic eruptions can be slow and fairly quiet or violently explosive. When a volcano erupts it can create new land, but it can also cause great destruction to the environment and human habitats.
Volcanic hazards include but are not limited to landslides, mudflowsnoes
, earthquakes, increased fire hazard, explosions, flash flooding, and tsunamis. Volcanoes may produce an abundant amount of volcanic ash that can spread thousands of miles and have the following effects: breathing difficulties, contaminated water supplies, collapsed roofs, disrupted machinery, and failure of jet engines while flying.
Volcanic eruptions can destroy plants and produce more greenhouse gases in the atmosphere. Mammals and insect life, along with their habitats, can also be destroyed. The benefit of volcanic eruptions in an ecosystem is that the soil becomes very nutrient rich, so the chance of plant life returning back is highly likely.
Tornadoes
Also referred to as twisters or cyclones, tornadoes are violently rotating columns of air that whirl at high speeds of 250 mph or more. Tornadoes are shaped like a funnel that can extend in one mile wide and 50 miles long. Thunderstorms often produce large hail, strong winds, and tornadoes.
High winds from the tornado and hail from the thunderstorms, cause the most damage by destroying buildings and vehicles, killing humans and animals, uprooting trees, and scouring the soil off the ground down to the rock. Any vegetation that survives could then multiply and overpopulate the region, thereby hampering plant and animal interaction.
Tornadoes funnel downward from cumulonimbus clouds toward the ground. Upon reaching the surface of the ground, tornadoes pull up the dirt and debris and take on the color of the material. Two or more tornadoes may form at the same time. A waterspout is a weak tornado that forms over water. Once over the land, the waterspout evolves into a tornado.

5. Earthquakes
An earthquake is a massive amount of energy that occurs as a result of drastic shifts in the Earth’s crust. This release of energy can be caused by a volcanic activity or the movement of plates. As pressure from the plates builds and exceeds the strength of the rock, the plates break and snap into new positions. This process releases pressures in the crust and the Earth’s crust reaches equilibrium again. Grade 7 Science Unit: 04 Lesson: 01
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Earthquakes are measured by seismic waves. As the crust breaks, seismic waves are created. The waves travel at various speeds outwardly from the source of the earthquake depending on the magnitude of the shock and what material the wave moves through.
Earthquakes can open large cracks in the ground, causing standing bodies of water such as ponds or lakes to disappear. Land on either side of the fault can raise, lower, or move away or toward each other. Earthquakes can cause damage to the environment by liquefaction (liquefying) of the ground, landslides, avalanches, fires, or tsunamis. The main impact to humans is property damage and loss of life.
Tsunamis
Tsunamis are ocean waves produced by earthquakes, volcanic eruptions, meteorite impact, or underwater landslides. Tsunamis are a series of waves that can travel between 450–600 mph in the open ocean. Before a tsunami’s approach the shore, the tide will recede from the coastline followed by a series of waves that travel outward in all directions. When tsunamis come ashore, their speed slows but their height rises bringing a raging surge of debris filled water. Areas of risk include low-line elevation along coastlines.
Tsunami’s can cause both extreme environmental destruction and human tragedy by drowning, flooding, contamination of drinking water, loss of habitat or housing, fires from broken gas lines, etc.
Floods
A flood is an overflowing of water onto land that is normally dry. Floods are often caused by extreme weather such as severe thunderstorms, hurricanes, monsoons, and melting snow and ice. Floods can last from a few minutes to months. The duration of floods depends upon the amount of water accumulated, porosity of the soil and the amount of water already in the soil.
Humans have altered the landscape in several ways. The greatest impact results from paving the ground for housing, roads, and parking lots. Neither asphalt nor concrete is porous. All the precipitation that falls becomes runoff. Much of the world’s population lives near the coast or on floodplains. Floods can cause loss of life, disease, property loss or damage, contamination of drinking water, and destruction of crops and livestock.