Chile’s Geomorphology and Natural Hazards

Posted on Feb 23, 2025 in Geology

Regional Geomorphology of Chile

Chile’s regional geomorphology can be broadly categorized into five main units:

  1. Andes Mountains
  2. Precordillera (Foothills)
  3. Intermediate Depression
  4. Cordillera de la Costa (Coastal Range)
  5. Coastal Plains
  • Andes Mountains:
    • Average height generally does not exceed 2000 meters.
    • Some volcanic peaks reach 3000 meters, including Chillán and Antuco volcanoes.
    • Characterized by bulky and plateau-like forms, with some acute or prominent low-profile features.
    • Features valleys formed by the Ñuble, Laja, and Biobío rivers.
  • Precordillera (Foothills):
    • Lower elevation terrain consisting of terraced hills at the foot of the Andes.
    • Average height ranges from 400 to 500 meters.
  • Intermediate Depression:
    • Altitude around 150 meters.
    • Lower zones near the Itata and Ñuble rivers.
    • Wider areas in Chillán and the Laja plain.
  • Cordillera de la Costa (Coastal Range):
    • North of the Biobío River: Solid, mature, gently rolling hills.
    • Average height of 400 meters.
    • Some hills, such as Cerro Callumanque (764m) and Cerro Queimada (548m).
    • South of the Biobío River: The range acts as a barrier (Nahuelbuta), hindering climate and transportation between Lebu and Angol. Cerro Nahuelbuta reaches 1470 meters.
  • Coastal Plains:
    • Elevation between 80 to 100 meters.
    • Notable areas include Cobquecura, the mouth of the Itata River, Coliumo-Dichato, Lirquén, the coastal plain of Concepción-Talcahuano, and the coastal plain of San Pedro-Coronel.

Natural Hazards in Chile

  • Seismic Risk:
    • Caused by the movement of continents and ocean floors (plate tectonics).
    • The Earth’s crust is composed of 12 plates with varying densities and shapes. These plates interact, causing collisions, separations, or subduction.
    • Plate movement speed is approximately 10 cm per year, and 1.5 cm per year for the Antarctic and South American Plates.
    • In Chile, earthquakes result from the interaction between the Nazca Oceanic Plate and the South American Continental Plate.
    • Includes natural seismicity (small earthquakes), major earthquakes, and aftershocks (plate adjustments with decreasing strength and frequency).
  • Tsunami Risk:
    • Monitored by SHOA (Hydrographic and Oceanographic Service of the Chilean Navy).
    • Tsunamis are a series of ocean waves that can travel at speeds exceeding 900 km/h.
    • Coastal arrival can manifest in two ways:
      1. Water receding, a natural warning sign.
      2. Rapid sea-level rise.
    • Tsunamis are typically triggered by strong seismic events (greater than 7.5 magnitude) with an epicenter at sea and a vertical displacement.
  • Volcanic Risk:
    • Volcanoes are formed by the increase of the temperature in the deep, liquid and gaseous materials that began to migrate and reach the surface and be expelled violently.
    • Hazards associated with volcanic processes include:
      • Lava eruptions
      • Tephra fall
      • Flood formation
      • Gas emissions
      • Acid rain generation
      • Pyroclastic flows or surges
      • Volcanic avalanches
  • Weather Risk:
    • Natural processes involving the transport of materials (rocks, soil, mud, water) that can modify the landscape. Water is the primary agent.
    • Phenomena include:
      • Floods
      • Flash floods
      • Alluvial events
      • Avalanches
      • Landslides
      • Snowstorms and storm surges
    • Solutions involve removing vulnerable populations or intervening in the causes (e.g., for flash floods: avoiding construction in high-risk areas, managing catchments, expanding rainwater collectors).