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Short answer

A landslide is rock, debris or soil moving downslope, at speeds from inches per year to tens of miles per hour. It happens when the downhill pull of gravity beats the strength of the slope, and almost every landslide has more than one cause. [S1][S2]

Key points

• Landslides occur in all 50 states and U.S. territories. [S1]
• Triggers include heavy rain, snowmelt, earthquakes and volcanic activity. [S2]
• People can contribute by building roads and structures without proper grading, changing drainage, or disturbing old landslides. [S2]

Claims

• id: C1 claim: Landslides occur in all 50 states and territories. source: S1 evidence: "Landslides occur in all 50 states and territories"
• id: C2 claim: Landslides are downslope movement of rock, debris, and soil. source: S1 evidence: "Landslides are the downslope movement of earth materials (rock, debris, and soil)"
• id: C3 claim: Almost every landslide has multiple causes. source: S2 evidence: "Almost every landslide has multiple causes."
• id: C4 claim: Human activities can contribute to landslides. source: S2 evidence: "in some cases human activities can be a contributing factor in causing landslides"

Sources

• [S1] Landslide Basics. USGS. https://www.usgs.gov/programs/landslide-hazards/landslide-basics . License: US government work, public domain. Accessed 2026-11-04.
• [S2] What is a landslide and what causes one?. USGS. https://www.usgs.gov/faqs/what-a-landslide-and-what-causes-one . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_a9fwf1tk,
  author = {{iinventedlight}},
  title = {{What is a landslide and what causes one?}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/landslide-basics/},
  note = {Permanent ID iil:note:a9fwf1tk. License: CC-BY-4.0.},
}

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