Lecture 8 - From Rocks to Soils and then Plants

Question 1

What is weathering?

Answer 1

The chemical alteration and mechanical breakdown of rock.

Question 2

What does weathering do?

Answer 2

Converts rock to saprolite (in situ weathered rock) and then to soil.

Question 3

What is physical weathering linked to?

Answer 3

The exploitation and utilisation of joints.

Question 4

What is haloclasty?

Answer 4

Saline water seeps into rocks and then precipitates a salt.

The salt crystals grow and apply a force on the rock.

Question 5

What is granular disintigration?

Answer 5

Grain-by-grain breakdown of rock masses.

Question 6

What is frost wedging?

Answer 6

Water seeps into cracks in the rock and then freezes.

This increases the volume by 9% and so a force is exerted onto the rock.

Question 7

How does physical weathering occur via biology?

Answer 7

Plant roots can infiltrate into rocks and grow.

Question 8

What are the methods of weathering by plants?

Answer 8

Root exploration of cracks.

Retention of water.

Organic acid excretion from roots.

Uptake of selected ions causing increased solubility.

Decomposition of root and leaf remains releasing organic acids as decay products.

Encouraging biota to graze and disturb rock materials.

Question 9

How does moss colonising limestone cause it to weather?

Answer 9

Moss attracts and retains water which changes the chemical and physical environment of the rock.

This accelerates the process of chemical weathering.

Question 10

What are the four types of chemical weathering?

Answer 10

Hydrolysis

Acid dissolution.

REDOX reactions.

Chelation of polyvalent metals.

Question 11

What is hydrolysis?

Answer 11

Minerals of the rock dissolving and leaching out of the rock.

Question 12

What is acid dissolution?

Answer 12

Acidic water dissolves/reacts with rock minerals.

Question 13

What is an example of a weathering redox reaction?

Answer 13

Fe2+ oxidising to Fe3+.

Question 14

How does chelation of polyvalent metals cause weathering?

Answer 14

Citric acid from plant roots and microbes dissolving iron and aluminium.

Question 15

Which minerals are the most susceptible to weathering?

Answer 15

Olivine

Ca-rich plagioclase

Pyroxene

Amphiboles.

Question 16

Which minerals are the least susceptible to weathering?

Answer 16

Biotite

Na-rich plagioclase

K-feldspar

Muscovite

Quartz

Question 17

How do temperature and rainfall affect the type of weathering that occurs?

Answer 17

High rainfall and high temperatures lead to high rates of chemical weathering.

Lower rainfall and low temperatures lead to high levels of mechanical weathering.

Question 18

What is the rate of weathering proportional to?

Answer 18

The specific surface area (m² g⁻¹).

Question 19

What is a positive feedback mechanism that occurs during weathering?

Answer 19

As the mineral weathers, the specific surface area increases which causes the weathering rate to increase.

Question 20

What soil conditions do ultrabasic rocks cause?

Answer 20

High levels of magnesium, iron, nickel and chromium.

Low levels of calcium, potassium and phosphorus.

Question 21

What plants can live in soils created by ultrabasic intrusive rocks?

Answer 21

Highly selective, unique, endemic floras.

Question 22

What are zonal soils?

Answer 22

Well developed soils that reflect the influence of climate as the major soil-forming factor.

Question 23

What are intrazonal soils?

Answer 23

Well-developed soils formed where some local factor is dominant.

Question 24

What are azonal soils?

Answer 24

Soils that are immature and poorly developed.

Question 25

What plants can live in soils derived from basic intrusive rocks (plagioclase feldspar, pyroxene and amphiboles)?

Answer 25

Fairly selective fauna.

Question 26

What plants can live in soils derived from neutral and acidic intrusive rocks?

Answer 26

A range of plants due to zonal soils.

Question 27

What plants can live in soils derived from basic extrusive rocks?

Answer 27

Good plant cover with a high diversity due to zonal soils.

Question 28

What plants can live in soils derived from intermediate extrusive rocks?

Answer 28

Good plant cover and diverse flora due to zonal soils.

Question 29

What plants can live in soils derived from acidic extrusive rocks?

Answer 29

Poor plant cover that is low in nutrients due to azonal soils.

Question 30

What soils does sandstone form?

Answer 30

Acidic free and draining soils.

Question 31

What soils does shale form?

Answer 31

Less acidic and less free draining soils.

Question 32

What soils does limestone form?

Answer 32

Alkaline soils with lots of calcium carbonate.

Highly specialised plants live here.

Question 33

What is the soil type at Dark Peak?

Answer 33

Acidic moorland due to millstone grit.

This landscape is dominated by heather.

Question 34

What is the soil type at White Peak?

Answer 34

Alkaline grassland due to carboniferous limestone.

Alkaline grassland with a rich diversity of calcicole (chalk dwelling) species.

Question 35

What is a metallophyte?

Answer 35

A plant that can withstand high metal concentrations.

Question 36

What is phytomining?

Answer 36

Plants absorb metals from the soil when they grow.

The plants are then harvested and the metals collected.