How do snow crystals form?
What will be an ideal response?
Snow forms as ice crystals in clouds. In the same way that water droplets form around cloud condensation nuclei (Chapter 4), small ice crystals also form around tiny mineral or organic particles in the atmosphere referred to as freezing nuclei. At that point, the ice crystal can grow and take a variety of forms, largely as a function of temperature. The dominant process is one of deposition—the ice forms directly from water vapor (rather than the freezing of liquid water). Once the ice crystal forms, it continues to grow primarily by deposition. In the absence of freezing nuclei, pure water will not freeze until temperatures in the cloud drop to 233K (-40oC). This means that once temperatures drop below 273K and some ice starts to form around freezing nuclei, the cloud will consist of a mixture of ice crystals and supercooled water droplets (liquid water that is colder than 273K is referred to as supercooled water). The saturation vapor pressure for ice and liquid water are the same at 273K. As the temperature drops, however, the saturation vapor pressure with respect to ice decreases. This means that as far as the ice is concerned, the air is supersaturated and water vapor will deposit directly on the ice to grow the ice crystal. In doing so, that lowers the vapor pressure of the air, which results in evaporation from the water droplets—and the ice crystals grow at the expense of the water droplets. In other words, the ice grows by direct deposition and moves from gas to solid without going through the liquid phase first. It is this process that gives rise to the common view of hexagonal snowflakes such as those in Figure 6-4.
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Places where volcanism occurs at an isolated volcano are called:
a. extinct volcanos b. volcano acres c. independent volcanos d. hot spots
The slope of a cold front is much gentler than the slope of a warm front
a. True b. False Indicate whether the statement is true or false
As a result of the landslide at the Vaiont Dam, northern Italy, in 1963, approximately 3000 people died ________.
A. when slope failure allowed the dam structure to be pushed downstream by the water pressure of the reservoir B. when the landslide impacted and destroyed the dam structure C. as their houses that had been built on the landslide were destroyed D. as a huge wave of water was displaced from the reservoir by the landslide E. as their houses were buried by the landslide
After the drought of the 1930's farmers in the Great Plains were encouraged to plant rows of trees across fields to decrease soil erosion. How would this reduce soil erosion?
A) The trees can serve as windbreaks to slow wind erosion. B) The trees helped shade the ground, retaining moisture. C) Tree roots would retard runoff and prevent erosion. D) The trees had no effect; they were just used to improve the land appearance after the great depression.