Geomorphology and Hydrology of Argentina's Landscapes

Geomorphology: Origin and Modification of Reliefs

Origin of Relief Structures

Geological structures were formed across different geological ages. For instance, the Andes Mountains were formed during the Cenozoic Era, while the mountains of Tandil date back to the Precambrian Era.

Factors Modifying the Earth's Relief

Relief modification is driven by both internal (endogenous) and external (exogenous) forces.

Endogenous Factors (Internal Forces)

These forces originate within the Earth and include:

• Orogenesis: The process of mountain formation, typically occurring when one tectonic plate subducts beneath another, creating folds and fractures that give rise to raised ridges.
• Volcanic and Seismic Phenomena: Including earthquakes and tsunamis.
• Epirogenesis: The large-scale lifting and sinking of the Earth's crust relative to the asthenosphere.

Exogenous Factors (External Forces)

These factors involve weathering and erosion caused by external agents:

• Fluvial Erosion: Wear caused by river water.
• Storm Erosion: The direct impact of rainfall on rocks and soils.
• Wind Erosion: Wear generated by the collision of particles carried by the wind against rocks and soil.
• Glacial Erosion: Weathering of rocks caused by the sliding movement of glaciers.
• Marine Erosion: Erosion resulting from the shock waves of the sea against coastal structures.
• Mechanical Erosion: Weathering primarily driven by temperature variations (e.g., freeze-thaw cycles).

Major Reliefs of Argentina

Mountains

• Very Old Mountains: Characterized by rounded tops, gentle slopes, and lower elevation.
• Newer Mountains: Characterized by higher elevation and steeper slopes.

The Andes Mountain Range

The Andes consist of numerous mountain ranges and high plateaus. The range narrows significantly from North to South across the country.

Plateaus

Plateaus are typically the result of extensive erosion.

• The Puna: High plateaus resulting from erosion and sediment accumulation.
• Patagonian Plateaus: Staggered plateaus that descend towards the sea, often dissected by river erosion forming valleys.
• Missionary Plateau: Formed from the old basement of the Brasilia Craton, shaped primarily by river erosion.

Plains

Plains are formed by the accumulation of eroded materials transported by various exogenous agents.

Hydrography and Water Systems

Water Distribution and Aquifers

Water distribution is not homogeneous across Argentina. Wetter areas feature more frequent rivers and streams carrying a higher volume. In drier areas, rivers are less frequent and are usually supplied by rainfall and snowmelt from distant sources. Most major rivers flow in a west-east direction. The most important aquifer in the region is the Guarani Aquifer.

Watersheds (Drainage Basins)

A watershed is a system formed by a river network and the surrounding surface area that drains into it.

• Exorheic Basin: Occurs when the main river discharges its waters outside the continent (e.g., into the sea).
• Endorheic Basin: Occurs when the main river fails to reach the sea, losing its volume and disappearing internally (e.g., through evaporation or infiltration).
• Arheic Areas: Areas that lack organized drainage basins, meaning water does not flow through defined river systems.

Water Balance and Hydrographic Regimes

Water Balance

The water balance refers to the accounting of all water entering and leaving a system over a specific time interval.

Hydrographic Regimes

River flow patterns are determined by their primary water source:

• Plata Basin: Characterized by a summer rainfall regime.
• Outfall Drainage Basins (Andean): Characterized by a nival (snowmelt) regime.
• Patagonian Region: Characterized by mixed rainfall and snowy winter regimes.

Climate Characteristics

Temperatures are generally higher in areas closer to the equator (or lower parallels). The country is significantly influenced by the Zonda wind, as well as weather systems originating from both the Pacific and Atlantic Oceans.