1. To see the different parts of a volcano see page 211 in your textbook.
2. High silica content means high viscosity magma. When there is high viscosity magma, it will not flow out of the volcano easily so explosive eruptions will be more likely.
3. A quiet eruption occurs when magma is low in silica content (low viscosity). Lava flows easily out of vents and volcanic gases bubble out of the lava. Pahoehoe and aa lava can be formed by quiet eruptions. Hazards from quiet eruptions are lava flows and fires.
4. Explosive eruptions occur when magma is high in silica content (high viscosity). Lava does not flow easily out of the volcano and gets clogged up in the volcanic vents. When the vents are clogged, pressure from the magma and volcanic gases builds up inside the volcano. When the volcano finally erupts it is an explosive eruption. This type of eruption will cause pyroclastic flow (rock particles of various sizes called ashes, cinders, and bombs). Ash fall, landslides, rock falls, and release of volcanic gases are hazards associated with explosive eruptions.
5. Changes at a volcano can signal to scientists that it may erupt. Scientists often use tools such as tiltmeter or GPS receivers to see if there is any movement or tilt of the ground at a volcano. Tilt and ground movement can indicate that a volcano may erupt soon. Earthquakes occurring at a volcano (often monitored by seismographs) can indicate that a volcano may erupt soon.
Also, volcanic gases escaping signal that a volcano may erupt soon.