Comment: 05:33 - 06:57 (01:24)
Source: Annenberg/CPB Resources - Earth Revealed - 16. Mass Wasting
Keywords: "mass wasting", creep, slope, soil, bedrock, gravity, water, season, Alaska, freeze, thaw, "geologic hazard"
Our transcription: At first glance, for example, this site appears tranquil and undisturbed, but a closer look reveals the presence of "creep," a sluggish form of mass wasting that sometimes moves as slowly as one centimeter per year.
Creep operates every day, everywhere, no matter how gentle the slope.
Creep occurs when the soil and uppermost part of the bedrock within a slope moves slowly downhill under the influence of gravity and water.
The wetting and drying of the uppermost ground material results in alternate expansion and contraction with gravity pulling the contracting Earth imperceptibly down slope.
This can happen even when the angle of the slope itself is very small, almost to the point of being horizontal.
Creep is especially active in regions where moist ground seasonally freezes and thaws, such as here in Alaska.
Each freeze thaw cycle moves soil particles downhill in minute increments.
And despite the fact that no one has ever died from creep, it does more long term economic damage than all other forms of mass wasting combined.
This can take the form of buckling railroad tracks or cracked building foundations, as well as broken underground water and sewer lines.
Geology School Keywords