Avalanche and Its SafetyAn 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 too 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 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 avalanches 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 likely 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-known 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 made. Observe the terrain and note obvious avalanche paths where plants are moiising or damaged. Avoid traveling below others who might trigger an avalanche.Giant StructuresIt is an impossible task to select the most amazing wonders of the modem world since every year more_wonderful_constructions appear. 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 TowersThe Petronas Towers were the tallest buildings in the world when they were completed in 1999. With a_height_of 452 metres, the tall 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 square 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 BridgeThe Millau Bridge was opened in 2004 in the Tam Valley，in southern France._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 from 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 DamThe Itaipu hydroelectric power plant is one of the largest constructions of its kind in the world. It consists of a series of dams 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 produced 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, 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 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. The waves washed floodwaters up to 2 miles inland a