11 - Amazon Case Study: Physical Factors influencing the Amazon

Question 1

Sedimentary Basins

How does Geology impact stores?

Answer 1

• The sedimentary basins occupy the low-lying areas of the Basin and are located primarily in the southern and eastern parts, such as in the northern region of Brazil and parts of the Guianas.
• These basins contain thick sequences of sedimentary rocks, such as sandstones, shales, and limestones, that were deposited over millions of years as the Basin filled with sediment from the surrounding highlands.
• These sedimentary basins have high porosity (can be up to 30% or more), allowing them to hold and transmit water through the interconnected pore spaces within sediment layers.
• One of the Sedimentary basins in the Amazon basin is the Solimões Basin which covers an area of approximately 40,00 square kilometres.
• It is estimated that the Solimões Basin has the capacity to store tens of billions to hundreds of billions of cubic metres of water.

Question 2

Crystalline rock

How does Geology impact stores?

Answer 2

• The crystalline shields are located primarily in the western and northern parts of the Basin, such as in the Andean mountain range to the west and the Guyana Shield to the north.
• Crystalline rocks are impermeable have low porosity (less than 0.1% porosity), and their water-holding capacity is limited to the small cracks and pores within the rock
• As such, in these areas there are low levels of infiltration and percolation which means they do not hold much water.

Question 3

Crystalline rock

How does Geology impact flows?

Answer 3

• The crystalline shields are located primarily in the western and northern parts of Basin, such as in the Andean mountain range to the west and the Guyana Shied to the north.
• Increased rate and speed of runoff in areas of impermeable rock, forcing water to flow into porous water basins
• When porous rock becomes saturated, runoff is rapid as water cannot infiltrate into the soil

Question 4

What is relief impact on stores?

Answer 4

• More water will infiltrate into the ground and be stored as ground water in regions of low relief
• Regions of steep relief will experience less infiltration and so there will be less ground water stored

Question 5

Areas of High Relief

What is relief impact on flows?

Answer 5

• Surface run-off is fastest in regions of steep relief, where water is unable to infiltrate as much and is aided by gravity
• In the west where is steeper (i.e. the steep slope of the Andes) there are much higher rates of surface run-off rates occurring because the water movement is aided by gravity.

Question 6

What is the temperature like in the Amazon?

Answer 6

• High temperatures throughout the year generate high rates of evapotranspiration from increased inputs of thermal energy.
• The average temperature in the Amazon region is around 26-27 degrees celsius
• Convection is strong, leading to high atmospheric humidity, the development of thunderstorms and intense precipitation

Question 7

What is the temperature impact on stores?

Answer 7

• Due to high temperatures, hence high amounts of rainfall (Either convectional or recycled rainfall) there is very dense vegetation and evergreen trees (which keep their leaves all year round) in the Amazon rainforest which leads to high interception rates.
• Hence there is a greater amount of water stored in the biosphere (due to greater amount of vegetation), but this is very short term storage as water is quickly evaporated and recycled
• High temperatures is part of the reasons that the Amazon’s air has a high absolute humdity. Warmer air can hold more water, so it generally results in an increase in absolute humidity.
• This means that there is a large amount water vapour stored in the troposphere, whcih is why Amazon’s air often looks ‘misty’.

Question 8

What is temperature impact on flows?

Answer 8

• A significant amount of rainfall in the amazon is convectional rainfall, this is when the ground is heated up causing parcels of air to rise, condense and then fall as precipitation.
• Due to high temperatures in the Amazon a lot of this convectional rainfall can occur
• Due to high temepratures in the Amazon there are very high evapotranspiration rates and 60% of rainfall that falls is recycled into the atmosphere through evapotranspiration.
• 20% of rain which is intercepted by vegetation is then immediately evaporated (this is called interception loss)

Question 9

Low relief

What is relief impact on flows and stores?

It might not all be stores or flows but you can link it easily

Answer 9

• Most of the Amazon Rainforest is lowlands
• The lowland areas of the Amazon rainforest are located primarily in the southern and eastern parts of the Basin, and are characterized by flat or gently rolling terrain with an elevation of less than 500 meters above sea level.
• In these areas of gentle relief water moves through soil as throughflow, groundwater flow and during high intensity events overland flow due to saturation of soils
• This can in turn lead to the river reaching peak discharge in it’s channel, which leads to a flood event if the river bursts its banks

Question 10

What are some of the most well-known lowland areas?

Answer 10

• Some of the most well-known lowland areas of the Amazon rainforest include the Brazilian states of Amazonas, Pará, and Mato Grosso, as well as the Peruvian departments of Loreto and Ucayali.

Question 11

What are some well-known highland areas?

Answer 11

• The highland areas of the Amazon rainforest are located primarily in the western and northern parts of the Basin, and are characterized by hills, plateaus, and mountains with elevations ranging from 500 meters to over 2,000 meters above sea level.
• Some of the most well-known highland areas of the Amazon rainforest include the Andean mountain range, which runs along the western edge of the Basin, and the Guyana Shield, which covers parts of northern South America.

Question 12

Why does higher temperatures lead to more evaporation?

Answer 12

Warmer temperatures generally result in more evaporation. Higher temperatures increase the kinetic energy of water molecules, allowing them to escape from the surface of bodies of water or soil more easily.

Question 13

Why do areas of low relief have high levels of infiltration?

Amazon Basin

Answer 13

• In areas of low relief in the Amazon basin, it is likely that there will be higher residence times in the soil compared to areas with higher relief. This is because low relief areas generally have gentler slopes and flatter terrain, which promotes higher levels of infiltration and water retention in the soil.
• As a result, water that infiltrates into the soil is likely to stay there longer, providing more opportunities for plant uptake and groundwater recharge.

Remember if the soils become saturated then this changes