Questions 6 through 11.
Listen to part of a lecture in a geology class.
You might expect that heavy snowfall is the main requirement for the formation of a glacier. But if you stop and think about it, you’ll realize there are lots of areas of the world that receive huge amounts of snow but have no glaciers. Snowfall alone isn’t enough. For a glacier to form, the snow can’t melt. It has to be conserved. In the extremely cold Arctic and Antarctic, there arc large areas that receive minimal precipitation and actually quality as desert Although there’s little snow, there are massive icc sheets because the snow that docs fall is conserved and transformed into ice.
Of course, lots of places do get large amounts of snow, and they do have glaciers … high mountains, for example. In high mountains where the climate is humid and cold, snowfall is frequent. Above the snowline, the annual snowfall exceeds the annual melting, so snow builds up. The accumulation is thickest in the hollows at the heads of valleys, because these locations are relatively high and cool, and are protected from sun and wind.
As snow accumulates in a hollow, it’s gradually converted to ice. First, the fragile snow crystals break as they’re compressed by the weight of more snow settling on top of them. There’s some melting and refreezing because of compaction, earth heat, and seasonal temperature fluctuations. So, the snow crystals are broken, then they’re wetted by meltwater, and re frozen, over and over again.
Gradually, aver time, the snowflakes change into grains. They become rounded and granular, like the grains of coarse sugar. There are pockets of air between the grains, connecting the grains to one another This old snow, called “firn,” is generally created after one complete winter-summer cycle.
Firn is actually bits of ice. The firn begins to re-crystallize, and eventually, it combines and crystallizes into solid ice a glacier. What happens is, the small grains coalesce to form large interlocking crystals of ice, with air trapped as hubbies inside the crystals. In the end, it’s pure ice. with all the air squeezed out The flow of the glacier down the mountain contributes to crystal growth, as the movement helps to compress the air out.
As the hollow in the valley head fills with snow turning to ice, the hollow enlarges, and the rock walls are carved out by shifting ice. As new snow is added, the lower part of the snow and ice mass bulges out, kind of like a mud pie. As the mass continues to bulge, part of the ice moves over the edge of the hollow and starts moving down the valley. Large glaciers usually move faster than small ones. Also, the movement is faster in the summer, when more meltwater is present beneath and around the ice mass to lubricate it and buoy it up.
Most valley glaciers move at a rate of., oh … between a few inches and a few feet a day. But some glaciers called surging glaciers can travel as much as 300 feet a day. There arc at least 200 of these surging glaciers in Alaska and the Northwest Territories. The surging is caused by a number of conditions, like … oh … sudden adjustment to an increase in the snow load on top, or, more likely, an mercase in the production of meltwater due to a rise in temperature. Glaciers that have more meltwater are better lubricated and tend to move faster than drier ones. In very cold climates, glaciers arc quite dry because of the lack of melting. The amount of water is slight, so the glacier docs not slide as quickly.
In warmer climates, glaciers are better lubricated with meltwater. They also cause more erosion, more carving out of the valley floor. Thu is because during the melt–freeze cycle, pans of the glacier freeze to the bottom and sides of the valley, and then, as the ice moves on, large chunks of glacier pluck out rock. So you can see why glaciers in warmer climates have a greater impact on the landscape than those in very cold climates.
Questions 12 through 17.
Listen to part of u talk in a theater class. The professor is talking about stages
Throughout the long history of theater, three basic types of stages have prevailed. Fach of these styles has advantages and disadvantages, and each is good for certain types of plays. Let’s take a look at the three styles and see why each has been so successful. The three designs are (1) the proscenrum or picture frame stage, (2) the arena or circle stage, and (3) the thrust stage with three quarter seating.
The first design, the proscenium stage, gets its name from the proscenium arch, the frame that sort of outlines the stage and separates it from the audience. The proscenium stage is also called the picture–frame stage because it looks like a large picture frame that the audience looks through to see the action of the play. The seats for the audience all face in the same direction, toward the stage at the front end of the theater.
The stage area of proscenium theaters is usually deep, and this allows for elaborate scenery and scene changes. Scenery pieces called backdrops are hung on ropes or cables at the rear, in layers, one behind the other. They’re called backdrops because they can be dropped into position and then raised again as necessary. The number of different backdrops possible allows the scene designer to create an extremely realistic set.
However, the proscenium arch also creates a distancing effect which is an advantage for certain types of drama, but a disadvantage for others. The proscenium works really well for large–scale productions with lots of characters and action, but for some plays for, example, close up views of real life the proscenium is sort of a barrier between the actors and the audience.
Next, the arena stage. In the past half-century, there’s been a movement to brtng theater closer to real life a movement toward more informal, more intimate theater. Thus, we have the arena stage also called the circic theater or theater-in-the- round. In the arena theater, the stage is in the center of a square or circle, with seats for the audience around it on all sides. The actors are in the center, so everyone in the audience can be close to them. The effect is a sense of intimacy, a kind of closeness that comes whenever people form a circle.
The arena is the oldest style of theater. It’s interesting to note that almost all early theatrical performances were “in the round,” as ceremonics, rituals, and dances in all parts of the world took place in a circle.
One disadvantage of the arena theater is that, while its design allows for intimacy, it also makes it impossible to have elaborate scenery or scene changes. This lack of flexibility is one reason why the third style of theater has become very popular again.
The third design the thrust stage falls somewhere between the proscenium and the arena styles In the thrust stage theater, the audience sits on three sides or in a half–circle, around a stage that sticks out into the center. Behind the stage is a stage house from which the actors enter and exit, and scenery is changed. The thrust stage is kind of a compromise between the proscenium and the arena styles. It combines the scenic feanires of the proscenium theater with the intimacy of the arena stage,
The formal English theaters of Shakespeare’s day were thrust stage theaters, and today it’s the most widely used of all the designs. Its advantages are obvious. It has the intimacy of three–quarter seating around the actors, and the stage house at the rear makes scene changes possible. Also, the fact that so many great dramatic works were written for it gives the thrust stage a prominent position among the other major forms.