1. Catastrophic events
TEKS 7.8A Predict and describe how different types of catastrophic events impact ecosystems such as floods, hurricanes and tornadoes.

2. Catastrophic events Before we can see how they affect ecosystems we need to understand how they form

3. HURRICANES How do Hurricanes Form?
Stage 1: A Tropical Disturbance Forms
Most Atlantic hurricanes begin life as organized clusters of thunderstorms off the west coast of Africa. These thunderstorms form along waves in the prevailing trade winds. The waves, called easterly waves, can be more than 2500 km (1550 mi) long. The cluster of thunderstorms is called a tropical disturbance.

4. How do Hurricanes Form?
Stage 2: The Tropical Disturbance Becomes a Tropical Depression
Most tropical disturbances die out, but some can continue to grow if they cross warm ocean water. Rising, warm air lowers the pressure and causes surface winds to rush in. The moisture carried aloft releases heat energy when it condenses. This causes more air to rise and surface winds to intensify further in a chain reaction that strengthens the storm. The system, which has now become a tropical depression, contains a distinct surface wind circulation with winds as high as 61 km/h (38 mph) and has started to rotate in a counter-clockwise direction due to Earth’s spin.

5. How do Hurricanes Form?
Stage 3: The Tropical Depression Becomes a Tropical Storm
When wind speeds in a tropical depression reach 63 km/h (39 mph), the system becomes a tropical storm. At this time, the storm is given a name following an alphabetical assignment each year. The structure and rotation of named tropical storms are better-defined than are those of a tropical depression.

6. How do Hurricanes Form? Stage 4: A Hurricane Forms
As air pressure in a tropical storm continues to drop, winds intensify. When the wind speed reaches 119 km/h (74 mph), a tropical storm becomes a hurricane. The structure of a hurricane is highly organized, and winds rotate around an eye which will typically form at its center.

7. How do Hurricanes Form? Stage 5: Landfall
When a hurricane moves ashore, it brings violent winds, heavy rains, and high ocean waves. Then as it moves over land, the storm is no longer able to feed on the energy it gets from the warm ocean, and it starts to slowly dissipate.

8. All the stages together

9. How are Hurricanes measured?
Interactive Showing Damage to Scale

10. How Hurricanes Affect the Ecosystem
First image to the left - Damage to the wetlands in the wake of Hurricane Katrina include the creation of ‘marsh balls’ (clumps of vegetation ranging in size from a basketball to a house).
Second image to the right - Chandeleur Islands, Louisiana.  Two years after Hurricane Katrina, the islands show minimal recovery since the storm impacted this area: the beach is still severely eroded, open breaches are common, and vegetation is sparse.

11. How Hurricanes Affect the Ecosystem
Aquatic Ecosystems
Sediment erosion and deposition often affect oyster beds and coral reefs.
Saltwater intrusion in freshwater lakes and streams causes massive fish kills and affects the lakeside habitat.

12. How Hurricanes Affect the Ecosystem
The hurricane floodwater often carries many toxic substances (Heavy metals, pesticides, ammonia, phosphate, untreated sewage)
These substance can cause degradation of water quality, phytoplankton blooms, a decrease in dissolved oxygen and harm to many organisms.
Hurricanes have minimal effect on oceanic ecosystems since the contaminants tend to be flushed out by tidal flows.

13. How Hurricanes Affect the Ecosystem
Terrestrial Ecosystems
Hurricanes wreak havoc on terrestrial ecosystems.
Strong winds, storm surge, flooding and tornadoes all have an impact.
Coastal wetlands and barrier islands take the brunt of the storm surge.
The storm surge causes sediment to erode and shift.

14. How Hurricanes Affect the Ecosystem
Many barrier islands end up shifted or eroded below sea level.
Mangrove forests are devastated by wind. These trees often become fuel for wildfires.
This forces birds to find other places to rest.
Saltwater intrusion from storm surge also changes the wetland ecosystems.
Sea grass beds are often destroyed.
These are critical to feeding and nesting for many animals

15. TORNADOES How do Tornadoes Form?
Tornadoes are among the most violent storms on Earth, with the potential to cause very serious damage.
                                               
Although no two tornadoes are the same, they need certain conditions to form - particularly intense or unseasonable heat.
As the ground temperature increases, moist air heats and starts to rise.

16. How do Tornadoes Form?
When the warm, moist air meets cold dry air, it explodes upwards, puncturing the layer above. A thunder cloud may begin to build.
                                               
A storm quickly develops - there may be rain, thunder and lightning.

17. How do Tornadoes Form?
Upward movement of air can become very rapid. Winds from different directions cause it to rotate.
                                               
A visible cone or funnel drops out of the cloud towards the ground.

18. How do Tornadoes Form?
The vortex of winds varies in size and shape, and can be hundreds of meters wide. A tornado can last from several seconds to more than an hour and may travel dozens of miles.
                                               

19. How do Tornadoes measured?
F0 (0-73mph) - Light damage: Some damage to chimneys. Branches broken from trees and some trees blown over.
F1 (73-112mph) - Moderate damage: Moving cars blown off roads, mobile homes overturned, or pushed off their foundations.
F2 ( mph) - Considerable damage: Mobile homes demolished, large trees snapped or uprooted, cars lifted off the ground.
F3 ( mph) - Severe damage: Trains overturned, most trees uprooted, heavy cars thrown, walls of homes destroyed.
F4 ( mph) - Devastating damage: Well constructed buildings destroyed, large objects thrown.
F5 ( mph) - Incredible damage: Cars thrown more than 100 metres, strong buildings swept away.
Winds within the tornado may be so fast they cannot be properly measured. Instead, the Fujita damage scale is used to estimate speed.
                                               
Interactive Site Showing Scale Damage

20. Tornadoes Effect on Ecosystems
Vegetation is uprooted.
Trees can be pulled out of the ground and carried to another location.
Organisms that live in or near these uprooted trees need to relocate.
This can cause a loss of species of organisms could also affect the interaction between plants and animals.

21. Tornadoes Effect on Ecosystems
The loss of plants caused by a tornado can allow new species of plants to grow in the cleared area.
Plants that survive can grow more abundantly then other species.
This loss of vegetation could also lead to soil erosion.

22. FLOODING
                                               

23. FLOODING
Flooding happens during heavy rains, when rivers overflow, when ocean waves come onshore, when snow melts too fast or when dams or levees break.
Flooding may be only a few inches of water or it may cover a house to the rooftop.
                                               

24. FLOODING Floods that happen very quickly are called flashfloods.
Flooding is the most common of all natural hazards.
It can happen in every U.S. state and territory.
                                               

25. Environmental Impact of Floods
Floods are important in maintaining ecosystem habitats and soil fertility.
Human attempts at managing flood prone areas disrupt the natural flood cycle.

26. Environmental Impact of Floods
Activities such as drainage of wetlands and land clearance for farming; upstream development that replaces natural vegetation with paved asphalt; and construction of channels, levees, reservoirs change the flood cycle and often result in increases runoff, destruction of riparian habitat, and increased water pollution

27. Effects of Floods
Floods destroy drainage systems causing raw sewage to spill out into bodies of water.
Buildings can be destroyed which can lead to many toxic materials such as paint, pesticide and gasoline being released into the rivers, lakes, bays, and ocean, killing marine life.
Floods cause significant amounts of erosion to coasts, leading to more frequent flooding if not repaired.
Floods positively impact the environment by spreading sediment containing nutrients to topsoil.

28. Effects of a Flood on the Ecosystem
Plants
On dry land, plant life can benefit from the sudden appearance of a large quantity of flood water.
Water stored underground will be replenished by the floodwater, while soil above ground will be able to soak up the water.
Plants will be able to receive water as a result.
The nutrients carried by the flood water can also revive deprived plants and aid in the germination of seeds.

29. Effects of a Flood on the Ecosystem
Plants Continued
Food water may prove a new lease on life for an area.
The soil is likely to be more fertile, leading to a suitable area in which to grow crops.
Flooding can kill woody and herbaceous plants.

30. How Flooding Affects Animal Breeding
The environment in are areas where floods have occurred are more suitable for the reproduction of species of birds and some other animals.
Fish can breed and give birth in the areas where flood water stays for an extended duration.

31. Animals Flooding forces many wild animals from their natural habitats.
Domestic animals are also left without homes after floods.
Rats may be a problem during and after a flood.
The large amounts of pooled water lead to an increase in mosquito populations.

32. Effects of Floods on Water-Based Ecosystems
Coral reefs are particularly at risk from the runoff from floods.
This runoff contains sediment and products such as pesticides and fertilizers, and will carry these into the ocean ecosystem.
Habitats may be destroyed, and animal and plant life are is likely to suffer.
Sediment may obscure the sunlight which inhibits photosynthesis of marine plants.

33. Effects of Floods on Water-Based Ecosystems
There are some benefits of flooding on the ocean ecosystems
The sudden appearance of an overflow of water can wash away unneeded salt, alongside man-made products like chemical waste.
This helps the flora and fauna thrive.
The flood water can also sweep away junk and debris which may have accumulated by the side of rivers.

34. THE END