The answer is all of the above;
Volcanic eruptions can cause debris to flows and make earthquakes happen because of the instability it can bring to the land during lava flow. Lava can also carry some objects to different places.
Another result would be floods and landslides. Volcanic eruptions can pull out trees and plants that can cause erosion and floods. There would be insufficient plants left to consume water from heavy rains. Lava can also cause wildfires in forests.
