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1、Avalanche and Its Safety An avalanche is a sudden and rapid flow of snow, often mixed with air and water, down a mountainside. Avalanches are among the biggest dangers in the mountains for both life and property. All avalanches are caused by an over-burden of material, typically snowpack, that is to
2、o massive and unstable for the slope that supports it. Determining the critical load, the amount of over-burden which is likely an avalanche, is a complex task involving the evaluation of a number of factors. Terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low risk
3、 of avalanche. Snow does not gather significantly on steep slopes; also, snow does not flow easily on fiat slopes. Human-triggered avalanches have the greatest incidence when the snows angle of rest1 is between 35 and 45 degrees; the critical angle, the angle at which the human incidence of avalanch
4、es is greatest, is 38 degrees. The rule of thumb2 is: A slope that is flat enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. Additionally3, avalanche risk increases with use ; that is, the more a slope is disturbed by skiers, the more li
5、kely it is that an avalanche will occur. Due to the complexity of the subject, winter travelling in the backcountry4 is never 100% safe. Good avalanche safety is a continuous process , including route selection and examination to the snowpack, weather conditions , and human factors. Several well- kn
6、own good habits can also reduce the risk. If local authorities issue avalanche risk reports, they should be considered and all warnings should be paid attention to. Never follow in the tracks of others without your own evaluations; snow conditions are almost certain to have changed since they were m
7、ade. Observe the terrain and note obvious avalanche paths where plants are moiising or damaged. Avoid traveling below others who might trigger an avalanche.Giant Structures It is an impossible task to select the most amazing wonders of the modem world since every year more_wonderful_ constructions a
8、ppear. Here are three giant structures which are worthy of our _admiration_ although they may have been surpassed by some more recent wonders. The Petronas Twin Towers The Petronas Towers were the tallest buildings in the world when they were completed in 1999. With a_height_ of 452 metres, the tall
9、 twin towers, like two thin pencils, dominate the city of Kuala Lumpur. At the 41st floor, the towers are linked by a bridge, symbolizing a gateway to the city. The American _architect_ Cesar Pelli designed the skyscrapers. Constructed of high-strength concrete, the building provides around 1，800 sq
10、uare metres of office space_on_ every floor. And it has a shopping centre and a concert hall at the base. Other _features_ of this impressive building include double-decker lifts, and glass and steel sunshades. The MiUau Bridge The Millau Bridge was opened in 2004 in the Tam Valley，in southern Franc
11、e. _At_ the time it was built，it was the worlds highest bridge, _reaching_ over 340m at the highest point. The bridge is described as one of the most amazingly beautiful bridges in the world. It was built to _relieve_ Millaus congestion problems. The congestion was then caused by traffic passing fro
12、m Paris to Barcelona in Spain. The bridge was built to withstand the _most_ extreme seismic and climatic conditions. Besides, it is guaranteed for 120 years! The Itaipu Dam The Itaipu hydroelectric power plant is one of the largest constructions of its kind in the world. It consists of a series of d
13、ams across the River Parana, _which_ forms a natural border between Brazil and Paraguay. Started in 1975 and taking 16 years to complete, the construction was carried out as a joint project between the two _countries_. The dam is well-known for both its electricity output and its size. In 1995 it pr
14、oduced 78% of Paraguays and 25% of Brazils _energy_ needs. In its construction, the _amount_ of iron and steel used was equivalent to over 300 Eiffel Towers. It is a _truly_ amazing wonder of engineering.Animals “sixth sense” A tsunami was triggered by an earthquake in the Indian Ocean in December,
15、2004. It killed tens of thousands of people in Asia and East Africa. Wild animals, however, seem to have escaped that terrible tsunami. This phenomenon adds weight to notions that I they possess a “sixth sense” for disasters, experts said.Sri Lankan wildlife officials have said the giant waves that
16、killed over 24,000 people along the Indian Ocean islands coast clearly missed wild beasts, with no dead animals found.“No elephants are dead, not even dead rabbit. I think animals can sense disaster. They have a sixth sense. They know when things are happening.” H.D. Ratnayake, deputy director of Sri Lankas Wildlife Department, said about one month after the tsunami attack.
