(10) Planet Blue




Hurricanes and Tornadoes

 Hurricanes are strong cyclones that originate in the oceans, near the tropics. They are accompanied by heavy rainfall and winds blowing at speeds of 75 mph.

Categories of Hurricane

Hurricanes are classified into five categories, based on their wind speeds and potential to cause damage.

• The World Meteorological Organization gives names to hurricanes.

• Hurricanes that form in the western Pacific Ocean are called typhoons.

• Hurricane season is the time when most Atlantic Ocean hurricanes occur.

• The eye is the calm and roughly circular center of a hurricane.

• Some tornadoes can have wind speeds of more than 300 mph.

• The word tornado comes from the Spanish word tronada, which means thunderstorm.

Hurricanes Wind velocity

Category One Winds 74–95 mph

Category Two Winds 96–110 mph

Category Three Winds 111–130 mph

Category Four Winds 131–155 mph

Category Five Winds greater than 155 mph

A tornado is a rotating violent wind that extends towards the ground from the clouds. Tornadoes are funnel-shaped with their narrow end towards the ground.


Tsunamis are tidal waves that occur on the surface of the ocean. They are caused by earthquakes and volcanic eruptions under the sea.

• Tsunamis are surface gravity waves.

• Tsunami waves can travel across the ocean at speeds of more than 500 mph.

• Japan is a nation with the most recorded tsunamis in the world.

• The 2004 Indian Ocean tsunami is the deadliest tsunami in recorded history.

• Tsunamis are most prevalent in the Pacific Ocean.

• 3.5 billion years ago, an asteroid collision created a giant tsunami that swept around Earth several times.

• When the ocean is deep, tsunamis can cross the entire ocean in a day or less.

• It is believed that a tsunami sounds like a freight train.

• Tsunamis can even travel up rivers and streams that lead to the ocean.


A megatsunami is an informal term used to describe a very large tsunami wave.

Rising High

Once the tsunami wave reaches the coast, its top moves faster than the bottom, which causes the sea to rise dramatically


Oceans were formed as a result of the redistribution of mantle materials within Earth, as they rose to the surface. Millions of years ago, as Earth warmed, lava, gases, and water vapor locked in Earth’s crust were released. These were carried to the surface by volcanic activity and formed the early atmosphere. Water vapor condensed into clouds bringing the first rain on Earth. Once the water cycle began, oceans starting forming.

The highest tides on Earth are found in the Bay of Fundy east of New Brunswick, Canada.

• The largest waterfall on Earth is actually underwater, found in the Denmark Strait.

• About 97% of all of Earth's water is saltwater found in oceans.

• The temperature of most ocean water is about 39° F.

• 90% of all volcanic activity occurs in the oceans.

• The pressure at the deepest point in the ocean is more than eight tons per square inch.

• The top ten feet of the ocean hold as much heat as the entire atmosphere.


Tides are the periodic rise and fall in the ocean’s surface caused by the gravitational attraction between Earth and the moon.

Oceanic Ridge

Oceanic ridges are mountains under the oceans formed by the movement of tectonic plates

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