Trust me, you don't want to get caught under a tsunami! Tsunamis are one of the world's most powerful natural forces.【小题1】

But do you know exactly what a tsunami is? It is huge, powerful waves in the ocean that grow as they reach the shore.【小题2】An earthquake happens when a big piece of the Earth's crust（地壳）suddenly moves. When the piece of ocean floor moves, it creates big holes. The water floods in to fill these holes. When the water moves that quickly, it creates a huge wave.【小题3】

Other natural disasters like landslides, volcanic eruptions, and glaciers breaking off can also cause tsunamis. Once the water starts moving because of the force of the disaster, large waves begin to spread.【小题4】They have been recorded at speeds from 400 up to 500 miles per hour! They can also move across very long distances.

At first, the waves of the tsunami may not seem that tall. That's because when the waves travel through the deep parts of the ocean, the top of each wave is very short. But as that wave comes near to the coast, it grows in height.【小题5】If you are sitting on a beach, you may not see the wave coming at first. But when the wave arrives, it will be like a towering wall of water. Some waves are as tall as 100 feet high.

In 2015, Chennai was destroyed by one of the worst floods in over a century, leaving thousands without food, water and supplies. During the flood, many heroes arose, one of whom was Santosh, a young man who owned a take-out restaurant in Chennai.

When the first flood hit in November, he got a call from a company called Naga Rava. The company asked him to prepare 5, 000 packets of food and give them to the flood victims, He. with his partners, took the order, cooked for 14 hours and delivered them. But that night, as they sat together discussing the event of the day, they actually felt ashamed. “Here was a man not even from Chennai and he was going out of his way to help the affected people. We, while living here, had not really done anything ourselves for our own people, ”said Santosh later.

He then began the groundwork for a collection to help cook more dishes. Little did he know that the November flood was just the beginning, and the real show was about to begin. The December flood affected them all. His own house got flooded and his family was trapped on the second floor. They lost phone connection and electricity. Despite this, Santosh went back out into the flood, creating a kitchen and preparing food all by himself for the victims. He did not sleep for four days, taking a one-hour break every day as he kept on cooking. As word got out about this man's effort, others stepped out to join him. From children to the elderly, strangers came to help him in cooking, packing and transporting food. Up to 300 volunteers worked together to make it all happen. By the time the fourth day finally came to an end, Santosh and his team had prepared 170, 000 food boxes and delivered them to people in need.

Scientists this week announced that lightning can travel much farther and last much longer than previously thought.

The conclusion is based on observations of a storm in Oklahoma that produced a lightning bolt (霹雳) nearly 200 miles long, nearly half the width of the state. The longest-lasting flash was observed in southern France, where a single flash in 2012 lasted for 7.74 seconds. Most lightning bolts last less than a second and travel only a few miles.

“We should be more aware of lightning if we can have lightning that can travel 200 miles.” said Randy Cerveny, the spokesman on weather and climate extremes for the World Meteorological Organization, which added for the first time, lightning to its list of extreme weather events. This list includes records for heat, cold, wind speed, rainfall and other events.

Scientists said that the Oklahoma lightning bolt shot from Tulsa, Okla. westward, nearly to the Texas border. It touched the ground in several places.

The lightning can start tens or hundreds of miles away and then come back to where we are. That’s why we have to be careful of where the lightning is coming to ground, even though the storm is past.

Of course not all storms have extreme lightning like that observed in Oklahoman and French storms. The Oklahoma bolt came in the midst of a particularly bad patch of weather early on June 20, 2007.

“Most lightning will strike within the 30-30 rule,” said Dr. Cerveny. “The 30-30 rule is one that we still want to stress and make sure people are aware of... but it does confirm that lightning can hit far from where the storm actually is.”

The “30-30” rule stipulates (规定) that if thunder follows lightning within 30 seconds, people should go inside for 30 minutes. If it lasts longer, it’s safe to stay outside.

Studying lightning is important because it can be fatal when it strikes. This year, 35 deaths have been blamed on lightning striker, according to data from the National Oceanic and Atmospheric Administration. That’s the highest death toll related to lightning strikes in any single year since 2007, reports The Weather Channel.

Though thunder is just the sound of lightening, the rumble(隆隆声) arrives after the light flash during a storm, because light travels much faster than sound. The booming sound is a shock wave caused by the rapid expansion of air suddenly heated by the lightning holt.