سؤال قراءة ستيب محلول — المفردات في السياق (تدريب 5909)

Avalanches are mass movements of snow and ice, they move very fast and average speeds are 40/60 km/h, but speeds of up to 200 km/h have been recorded in Japan, Loose avalanches, made of fresh snow, usually occur soon after a large full of snow. By contrast, slab avalanches occur at a later date, when the snow has developed some cohesion and unites together more, Slab avalanches are usually much larger than loose avalanches and cause much more destruction. They are often started by a sudden rise in temperature, which causes melting. This lubricates the slab and makes it unstable. Many of the avalanches occur in spring when the snowpack is large and temperatures are rising. There is also a relationship between the number of avalanches and altitude. For example, in the Swiss Alps most occur between 2000 meters and 2500 meters and there is diminished occurrence both higher up and lower down. The word slab in the passage is closest in meaning to ……………..