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CEGEOLO EV > (MODULE 9.1) SOIL FORMATION > Flashcards

(MODULE 9.1) SOIL FORMATION Flashcards

1
Q

geologists call soil ___.

A

regolith

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2
Q

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

A

soil

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3
Q

soil consists of ___.

A

grains with water and air in the voids between grains

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4
Q

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

A

soil horizons

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5
Q

the uppermost layer that consists entirely of organic material

A

O horizon

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6
Q

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

A

A horizon

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7
Q

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

A

E horizon

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8
Q

the E horizon is also called the ___.

A

zone of leaching

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9
Q

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

A

B horizon

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10
Q

the B horizon is also called the ___.

A

zone of accumulation

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11
Q

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

A

bedrock

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12
Q

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

A
  1. parent material
  2. slope
  3. living organisms
  4. climate
  5. time
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13
Q

how does time affect soil formation?

A

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

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14
Q

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

A

residual soils

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15
Q

residual soils have characteristics that depend on its ___

A

parent rock

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16
Q

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

A

depth; high density causing it to be more compact.

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17
Q

examples of residual soils
1.
2.
3.

A
  1. decomposed granite
  2. saprolite
  3. laterite
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18
Q

sandy residual soil from granitic rock

A

decomposed granite

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19
Q

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

A

saprolite

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20
Q

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

A

laterite

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21
Q

residual soils are often seen in ___

A

mountainous areas

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22
Q

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

A

transported soils

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23
Q

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

A
  1. gravity
  2. running water
  3. glaciers
  4. wind
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24
Q

transported soils are found in ___

A

spots far from their original spot

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25
Q

soils transported downslope by gravity

A

colluvial soils

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26
Q

types of downslope movement: ___ and ___

A

slow and rapid

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27
Q

slow downslope movement is called ___

A

creep

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28
Q

rapid downslope movements include ___ or ___

A

landslides or mudflows

29
Q

gravity deposits tend to be ___ and ___.

A

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

30
Q

colluvial soils are often found at ___

A

the bottom of a slope

31
Q

soils transported by moving water

A

alluvial soils

32
Q

alluvial soils are also known as ___ or ___

A

fluvial soils or alluvium

33
Q

alluvial soils are found in ___

A

the vicinity of rivers

34
Q

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

A

extensive groundwater aquifers

35
Q

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

A

moderately good engineering properties; fair to good support

36
Q

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

A

aquifer

37
Q

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

A

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

38
Q

alluvial soils deposited and accumulates for a long time

A

alluvium

39
Q

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

A

alluvial fans

40
Q

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

A

natural levees

41
Q

alluvial soils deposited beneath lakes

A

lacustrine soils

42
Q

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

A

poor to average

43
Q

alluvial soils deposited underwater, formed in the ocean

A

marine soils

44
Q

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

A

deltas

45
Q

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

A

poor

46
Q

transported soils resulting from the action of glaciers

A

glacial soils

47
Q

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

A

mixture of minerals from different sources

48
Q

soil deposited directly by glacier

A

till

49
Q

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

A

ablation till

50
Q

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

A

moraines

51
Q

glaciers move with respect to the ___.

A

seasons

52
Q

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

A

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

53
Q

soil caught beneath the glacier

A

lodgement till

54
Q

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

A

heavily consolidated

55
Q

a lodgement till is sometimes called ___

A

hardpan

56
Q

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

A

very difficult to excavate

57
Q

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

A

glaciofluvial soil

58
Q

glaciofluvial soil is also called ___

A

outwash

59
Q

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

A

more uniform than till; sand and gravel

60
Q

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 ___

A

glaciolacustrine and glaciomarine soils

61
Q

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

A

soft and compressible; shear failure and excessive settlement

62
Q

soils transported by wind

A

aeolian soils

63
Q

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

A

very poorly graded; strong sorting power

64
Q

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

A

very loose; fair engineering properties

65
Q

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

A

sand dunes

66
Q

a loamy deposit formed by wind

A

loess

67
Q

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

A

very high porosity

68
Q

loess is fairly ___, but becomes ___.

A

strong when dry; weak when wet

69
Q

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

A

minimal; flatter; able to enter the soil

CEGEOLO EV (14 decks)

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