What types of external factors can influence an ecosystem?
There are multiple external factors that will affect an ecosystem.
In reference to the field of Earth Science specifically and factors that are external to the ecosystem, earthquakes, volcanic eruptions, landslides, avalanches, loss of glacial mass, and others can all affect an ecosystem.
Some of these effects will be drastic, such as a landslide that started at a higher elevation may immediately cover vegetation at a lower elevation. The effects of others may be felt over time, such as the loss of a glacier that once fed a river could mean that the river will dry up or experience significantly less flow during certain times of the year without the glacier acting as a reserve.
Volcanic explosions such as this one produce a large amount of ash, which may block more sunlight than usual in nearby ecosystems or cause pollution in the ecosystem:
Other factors that are related to Earth Science but would more likely be considered internal are processes and factors such as weathering, deposition, changes in precipitation, changes in soil composition, and other abiotic factors.