Answer:
16.C.
Gravity can make large volcanoes warp under their own weight in two ways: they can either spread outward on top of their "basement" of underlying rock or sag downward into that basement. The way volcanoes deform strongly influences the stability of their structures, and when and how they erupt.
17.C
Volcanoes spew hot, dangerous gases, ash, lava, and rock that are powerfully destructive. People have died from volcanic blasts. Volcanic eruptions can result in additional threats to health, such as floods, mudslides, power outages, drinking water contamination, and wildfires.
18.C.
Landslides can be initiated in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, stream erosion, changes in ground water, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors.
19.A
The impact of a landslide can be extensive, including loss of life, destruction of infrastructure, damage to land and loss of natural resources. Landslide material can also block rivers and increase the risk of floods.
20.C.
Earthquakes are usually caused when underground rock suddenly breaks and there is rapid motion along a fault. This sudden release of energy causes the seismic waves that make the ground shake. ... The earthquake is over when the fault stops moving. Seismic waves are generated throughout the earthquake.
21.A.
The primary effects of earthquakes are ground shaking, ground rupture, landslides, tsunamis, and liquefaction
