Why might a major volcanic eruption lead to cooler temperatures of earth's surface?

When a volcano erupts it releases a large amount of dust, smog, rock, and other materials. Basically, these bits and pieces float to form a metaphorical dust cloud. These clouds can often block out the sun like an ordinary cloud; however, because the cloud is dark, even less sun will be able to get through. So because the sun can't reach the ground, the temperature might decrease.

Ithink this is what you meant. the temperature at which a liquid begins to boil is called the boiling point. the boiling point of water is 212°f or 100°c.  and at that point will start to turn into steam (gas)

Olá. porque a reação na temperatura é muito rapida a do copo : )