TOEFL iBT Speaking. In this integrated speaking task, you will listen to part of

Listen to part of a talk in a geology class.
An important part of erosion is the phenomenon of mass wasting, the downslope movement of soil and loose rock, mainly due to gravity. Mass wasting moves material from higher elevations to lower elevations. Some types of mass wasting occur very suddenly, while others are more gradual.
One fast type of mass wasting is mudflow, the movement of material containing a large amount of water. Mudflows can move at speeds greater than one kilometer per hour and travel long distances. They usually result from heavy rains in areas with loose sediment. Because they happen so quickly, mudflows are catastrophic. However, mudflow is actually responsible for moving less material than the slower and less obvious action called creep. While mudflow occurs on steep slopes, creep occurs on gentler slopes.
Creep is the slowest type of mass wasting. It may take years for creep to have a noticeable effect. It involves the very gradual movement of soil and rock as a result of alternate freezing and thawing, or wetting and drying, which causes the surface material to expand and contract. Most vegetated slopes in humid climates are subject to creep, but it also occurs in deserts because even dry soil will creep as a result of daily heating and cooling.
Creep is more widespread than mudflow, but much less dramatic. When a mudflow occurs, we see direct evidence in downed trees and buried roads and buildings. With creep, the evidence is less obvious, usually in the form of bent trees, dips in roads and fences, and leaning utility poles. This is because the upper layers of soil move gradually, while the deeper layers stay fixed.
Using points and details from the talk, explain some of the differences between the mass wasting processes of mudflow and creep.