Final answer:
The factor that is not a trigger for mass wasting is 'regional drought' as it typically results in drier soil conditions, which are less likely to contribute to the instability of slopes needed for mass wasting events to occur.
Step-by-step explanation:
Triggers for Mass Wasting
Mass wasting, also known as landslides, refers to the downslope movement of rock and soil due to gravity. Various factors can trigger mass wasting events, including:
- Rainfall: Saturates soil, adding weight and reducing cohesion.
- Over-steepening of slopes: Erosion by rivers or the action of waves and glaciers create unstable slopes.
- Earthquake: Shakes and destabilizes slopes, leading to landslides.
However, one factor listed that does not trigger mass wasting is:
- Regional drought: Usually leads to a lack of moisture in the soil, which does not contribute to slope failure.
In summary, the option regional drought is not a trigger for mass wasting events unlike the other options which contribute to slope instability.