(MODULE 9.1) SOIL FORMATION

Question 1

geologists call soil ___.

Answer 1

regolith

Question 2

A layer of weathered, unconsolidated material that contains organic matter and is capable of supporting plant growth

Answer 2

soil

Question 3

soil consists of ___.

Answer 3

grains with water and air in the voids between grains

Question 4

soil layers are called ___ and can be distinguished from one another by appearance and chemical composition

Answer 4

soil horizons

Question 5

the uppermost layer that consists entirely of organic material

Answer 5

O horizon

Question 6

a dark-colored soil layer that is rich in organic matter and high in biological activity, both in plant and animal

Answer 6

A horizon

Question 7

organic acids and carbon dioxide produced by decaying plants in the topsoil that percolate downward from topsoil

Answer 7

E horizon

Question 8

the E horizon is also called the ___.

Answer 8

zone of leaching

Question 9

produced from downward movement of water in the E horizon and carries the dissolved minerals, and fine-grained clay minerals as well, into the soil layer below

Answer 9

B horizon

Question 10

the B horizon is also called the ___.

Answer 10

zone of accumulation

Question 11

the bottom of the soil horizon is unweathered parent material, also known as ___.

Answer 11

bedrock

Question 12

what are the factors affecting soil formation?
1.
2.
3.
4.
5.

Answer 12

1. parent material
2. slope
3. living organisms
4. climate
5. time

Question 13

how does time affect soil formation?

Answer 13

time affects the soil through weathering; the longer the soil is exposed to weathering, the more soil accumulates

Question 14

soils that remain in-place when the rock weathering process is faster than the transport process

Answer 14

residual soils

Question 15

residual soils have characteristics that depend on its ___

Answer 15

parent rock

Question 16

the engineering properties of residual soils range from poor to good, generally improving with ___ due to ___.

Answer 16

depth; high density causing it to be more compact.

Question 17

examples of residual soils
1.
2.
3.

Answer 17

1. decomposed granite
2. saprolite
3. laterite

Question 18

sandy residual soil from granitic rock

Answer 18

decomposed granite

Question 19

the general term for residual soils that are not extensively weathered and still retain much of the structure of the parent rock

Answer 19

saprolite

Question 20

residual soil cemented with iron oxides, which gives it a high dry strength

Answer 20

laterite

Question 21

residual soils are often seen in ___

Answer 21

mountainous areas

Question 22

such soils are formed when rock weathers at one side and the particles are moved to another location

Answer 22

transported soils

Question 23

transporting agents of transported soils:
1.
2.
3.
4.

Answer 23

1. gravity
2. running water
3. glaciers
4. wind

Question 24

transported soils are found in ___

Answer 24

spots far from their original spot

Question 25

soils transported downslope by gravity

Answer 25

colluvial soils

Question 26

types of downslope movement: ___ and ___

Answer 26

slow and rapid

Question 27

slow downslope movement is called ___

Answer 27

creep

Question 28

rapid downslope movements include ___ or ___

Answer 28

landslides or mudflows

Question 29

gravity deposits tend to be ___ and ___.

Answer 29

loosely compacted and exhibit little change in the general character of soil material

Question 30

colluvial soils are often found at ___

Answer 30

the bottom of a slope

Question 31

soils transported by moving water

Answer 31

alluvial soils

Question 32

alluvial soils are also known as ___ or ___

Answer 32

fluvial soils or alluvium

Question 33

alluvial soils are found in ___

Answer 33

the vicinity of rivers

Question 34

alluvial soils often contain ___ which are important in the development of water supply wells and in geo-environmental engineering

Answer 34

extensive groundwater aquifers

Question 35

most alluvial soils have ___ and provide ___ for buildings and other structures

Answer 35

moderately good engineering properties; fair to good support

Question 36

a soil that is very permeable; allows water to pass through easily

Answer 36

aquifer

Question 37

what condition would alluvial soils have in order to be considered not good soil?

Answer 37

a mixture of coarse sand, loose conditions, and water saturations, which leads to liquefaction

Question 38

alluvial soils deposited and accumulates for a long time

Answer 38

alluvium

Question 39

when a river's velocity decreases substantially, coarser soil particles settle, forming submerged, flat, triangular deposits known as ___

Answer 39

alluvial fans

Question 40

larger particles, such as sand and gravel, tend to settle more quickly to form ___

Answer 40

natural levees

Question 41

alluvial soils deposited beneath lakes

Answer 41

lacustrine soils

Question 42

the sustainability of lacustrine soils as foundation support ranges from ___ to ___.

Answer 42

poor to average

Question 43

alluvial soils deposited underwater, formed in the ocean

Answer 43

marine soils

Question 44

a special type of marine deposit formed where rivers meet larger bodies of water, and gradually build up to the water surface

Answer 44

deltas

Question 45

the engineering properties of marine soils are often ___ due to its silt and clay being very soft.

Answer 45

poor

Question 46

transported soils resulting from the action of glaciers

Answer 46

glacial soils

Question 47

glaciers grind down the rock and soil, transporting the materials over long distances, causing the deposits to contain a ___

Answer 47

mixture of minerals from different sources

Question 48

soil deposited directly by glacier

Answer 48

till

Question 49

soil that was bulldozed by the glacier then deposited in ridges or mounds

Answer 49

ablation till

Question 50

the ridges and mounds found in ablation till deposits are called ___ and are loose and easy to excavate

Answer 50

moraines

Question 51

glaciers move with respect to the ___.

Answer 51

seasons

Question 52

during the winter season and the summer season, what do glaciers do?

Answer 52

during the winter season, they move forward; at summer, they detract

Question 53

soil caught beneath the glacier

Answer 53

lodgement till

Question 54

the lodgement till is ___ under the weight of the ice.

Answer 54

heavily consolidated

Question 55

a lodgement till is sometimes called ___

Answer 55

hardpan

Question 56

while a lodgement till provides excellent support, it is also ___

Answer 56

very difficult to excavate

Question 57

when glacier melts, they generate large quantities of runoff that erodes till and deposits it downstream as ___

Answer 57

glaciofluvial soil

Question 58

glaciofluvial soil is also called ___

Answer 58

outwash

Question 59

glaciofluvial soil deposits are ___ than till and an excellent source of ___ for use in concrete aggregates

Answer 59

more uniform than till; sand and gravel

Question 60

the fine-grained portion of the till often remains suspended in the runoff water until reaching a lake or the ocean where it finally settles to the bottom. these are called ___

Answer 60

glaciolacustrine and glaciomarine soils

Question 61

glaciolacustrine and glaciomarine soils are ___ and are thus prone to problems with ___.

Answer 61

soft and compressible; shear failure and excessive settlement

Question 62

soils transported by wind

Answer 62

aeolian soils

Question 63

transportation through wind generally produces ___ soils due to the ___ of wind

Answer 63

very poorly graded; strong sorting power

Question 64

aeolian soils are usually ___, and thus have only ___.

Answer 64

very loose; fair engineering properties

Question 65

aeolian sands can form horizontal strata, which are interbedded with alluvial soils, or they form irregular hills called ___

Answer 65

sand dunes

Question 66

a loamy deposit formed by wind

Answer 66

loess

Question 67

due to the high deposition mode of loess, it typically has a ___.

Answer 67

very high porosity

Question 68

loess is fairly ___, but becomes ___.

Answer 68

strong when dry; weak when wet

Question 69

loess can be stable when cut to steep slopes where water infiltration is ___. it is unstable when the slope is ___ and water is ___.

Answer 69

minimal; flatter; able to enter the soil