Geology of Paraguay

Paraguay is a landlocked country in South America in which three ecoregions met; cerrado (a savannah), Atlantic forest, and chaco (a mix of the two). Areas in which ecoregions meet tend to have very high biodiversity. As an undergraduate I had plans, which sadly fell through, to travel to a research center in Paraguay. As part of the planning process, I did a lot of research on the country, including research related to the geology of the country.

Chaco_Boreal_Paraguay
An example of the Chaco

The bedrock in Paraguay is mostly from the Quaternary age and Carboniferous age, though some may be Permian. In more northern parts of the globe, like western New York, you don’t find Quaternary age rocks because the last glaciation period stripped them away. Older rocks are found in the western part of the country. The country is very flat, particularly in the area in which the research center is located. Over about 1.5 miles I walked to class every day as an undergraduate there was a 112-foot change in elevation. Compared to a 48-foot change in elevation over the 0.8 miles it would have taken me to get to my study area.

2000px-Paraguay_in_South_America_28-mini_map_-rivers29.svg_
For reference, Paraguay is in red

The country is home to the largest underground water source in the world; the Guarani Aquifer. The aquifer is named after the indigenous people of the area, you guessed it, the Guaranis. It is facing withdrawals from agricultural use in the area. In remote areas, there are not that many withdrawals from the aquifer as meteoric water or water derived from precipitation is abundant, but pollution is being caused by pesticides. It is also being degraded via runoff.  It’s worth noting that withdrawals have been limited due to a four-country agreement about the aquifer. The aquifer is also found under Argentina, Uruguay, and Brazil. The aquifer produced a lake near the research center called Laguna Blanc, which has sandy white beaches. Since we know the aquifer produces a lake, we also know that it is an unconfined aquifer.

Aquiferoguarani
The Guarani Aquifer

Coal, oil, and natural gas are not commonly found in the area, although areas with similar geology do have them. The country does not use natural gas at all and only uses some oil. Burning wood is also not as common as the forest produce poor burning wood. In fact, Paraguay produces the highest per capita surplus of electricity in the world, thanks to Itaipu Dam.  The dam was created by taking the largest waterfall by volume (Iguazu Falls)and impounded it. In 2004, the country produced 51.8 billion kilowatt-hours (Bkwh) of electricity while consuming only 3.1 Bkwh. The original waterfall was supported by a basalt formation that was likely created by old volcanoes in surrounding countries.

Itaipu_Aerea
Itaipu Dam

Assigning streams an order doesn’t really make sense in a country like Paraguay as the streams are ephemeral (meaning they only flow certain times of year) and dynamic. Sheet water plays a large role in shaping the cerrado. In the cerrado vegetation is sparse so erosion is very common. On the other hand, the Atlantic forest is able to hold soil in place and channel water due to a large number of plant roots. In some areas where slash and burn is common, there are water quality issues because of the sheet water runoff.

Paraguay is pretty safe from natural disasters besides floods. Floods are common as the country experiences a distinct dry and wet season. Thankfully, because the country is flat, landslides are very uncommon. Quicksand is however common due to the sudden change in pore pressure caused by heavy rains. The country is not near any plate boundaries so they are few earthquakes and no volcanoes, also no faults.

A rainshadow causes arid land in part of the country, near cerrado, as air has to travel over the Andes. When an air mass reaches the interior of a large continent it has grown quite dry. I couldn’t find where the sand in the cerrado comes from, but my guess is that is it caused by larger soil grains being washed away by sheet water over time, and plant roots did not hold in the soil. Rocks of the cerrado tend to be able to absorb more heat, so Atlantic forest plants do not survive there.

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