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Fall 2018 > Geology 101 Quiz 6 > Flashcards

Geology 101 Quiz 6 Flashcards

1
Q

sedimentary rocks form in one of two ways

A

(1) by accumulation and lithification of particles or (2) by precipitation from solution

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2
Q

in either case of formation, sedimentary rocks form by accumulating or precipitating what?

A

existing particles or ions

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3
Q

weathering

A

the process of breaking down rocks both physically and chemically

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4
Q

physical weathering

A

refers to physical breakage of rocks and minerals. Smaller pieces retain the same chemical and mineral structure

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5
Q

chemical weathering

A

refers to the chemical alteration of minerals by either complete dissolution, or by reactions that partially dissolve a mineral and leave a new mineral phase in its place

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6
Q

physical weathering: breaking rock down into smaller pieces can be done in two ways

A

fracturing and abrasion

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7
Q

fracturing

A

creating a break to separate one piece into two or more pieces

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8
Q

joints

A

fractures with no displacement on either side of the break

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9
Q

faults

A

fracture where the rock on one side of the break has moved relative to the other

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10
Q

abrasion

A

wearing away the surface of a rock by striking or scraping with other rock fragments

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11
Q

causes of fracturing (large scale processes to smaller scale)

A
  1. tectonics
  2. uplift and erosion
  3. cooling
  4. undermining
  5. ice wedging (or frost wedging)
  6. roots
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12
Q

tectonics

A

fracturing causes by tectonic plates moving

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13
Q

uplift and erosion

A

as overlying rock is removed, the reduced pressure allows the exposed rock to expand - since expansion is always uneven, the rock fractures

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14
Q

special cases of uplift and erosion can

A

produce layers of rock breaking away like layers on an onion (called exfoliation or spheroidal weathering)

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15
Q

cooling

A

as newly solidified igneous rock cools, it contracts; contraction is always uneven, and fractures develop

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16
Q

undermining

A

if erosion cuts away lower rock resulting in overhang, the rock will eventually fracture and fall

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17
Q

example of undermining

A

the Old Man in the Mountain (New Hampshire) gone in 2003

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18
Q

ice wedging (or frost wedging)

A

water expands when it freezes and can exert an incredible force; if water fills a crack and freezes, the expanding ice can widen the crack or cause the rock to completely split

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19
Q

roots

A

small roots can grow into a small fracture; as the root grows, it can widen the fracture or split the rock open

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20
Q

causes of abrasion (large scale processes to smaller scale)

A
  1. tectonic faulting
  2. glaciers
  3. landslides
  4. water carried rocks
  5. wind blown sand
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21
Q

tectonic faulting

A

where two plates slide past each other, rock can be pulverized and smeared along the fault

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22
Q

glaciers

A

glaciers trap blocks of rock in the ice that grind over rocks beneath the glacier; this process can grind rock so fine it is referred to as rock/glacial flour

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23
Q

landslides

A

as rocks fall, they strike other rocks and both break and abrade

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24
Q

water carried rocks

A

water borne rocks strike other rocks and slowly abrade the surfaces

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25
wind blown sand
in water, sand may travel around a rock without striking it due to the cushioning effect of the water; in air, the cushioning effect is reduced, and blowing sand strikes and abrades the surface - same principle as a sand blaster
26
fracturing and abrasion can reduce a mineral down to a powder, but it will not produce
most of the clay minerals commonly found throughout this area
27
chemical weathering is typically achieved by either
dissolution or oxidation reactions
28
two ways dissolution can occur
congruent and incongruent dissolution
29
congruent dissolution
complete dissociation of the atoms in the molecule
30
examples of congruent dissolution
halite: NaCl -> Na^+ + Cl^- calcite: CaCO3 -> Ca^2+ + CO3^2-
31
when a small crystal of halite or calcite is placed in water
it completely dissolves; no residue is left behind
32
if a large mass of halite or calcite is placed in water
the minerals completely dissolve until the water cannot hold any more of the dissolved ions, then dissolution stops (the portion that did dissolve, however, dissolves completely with no residue left behind)
33
incongruent dissolution
partial dissolution of a mineral resulting in a new mineral phase
34
example of incongruent dissolution
orthoclase to kaolinite (clay) - some of the ions of orthoclase are dissolved, some are rearranged in the new mineral (kaolinite) and water has been incorporated into the new mineral
35
? can enhance weather of some minerals
acid
36
acid is
simply a hydrogen ion H+
37
nature supplies its own acid by
dissolving carbon dioxide in water | CO2 + H20 -> H^+ + HCO3^-
38
in most cases, if water is actually part of the reaction, added acid will
increase the rate of reaction
39
sulfur and nitrogen emissions from burning fossil fuels (particularly coal) can
increase the acid content of rain (known as acid rain)
40
ancient sculptures made of limestone or marble (both calcite) heave weather must faster due to
acid rain
41
oxidation
alteration of a mineral by removing electrons, usually by oxygen
42
if electrons are removed, the charge on an ion changes, which means
the chemical formula must be altered to achieve charge balance
43
physical and chemical weathering ? each other
enhance
44
chemical weathering weakens the rock, which results in
faster physical weathering
45
common minerals that undergo incongruent dissolution and oxidation to produce clays & oxides
muscovite, K-feldspar, biotite, plagioclase, amphibole, pyroxene, olivine
46
common minerals that undergo congruent dissolution and totally dissolve
quartz, calcite, halite
47
weathering rates are increased by
1. contact with water 2. contact with air (CO2 and O2) 3. higher temperature
48
weathering is greatest in what kind of climates?
hot and humid
49
solids also increase weathering by
retaining moisture and facilitating root action
50
soil
weathered rock plus organic material (humus); typically layered
51
the layers of soil are referred to as
horizons
52
entisols
soils without layering
53
vertisols
contain expandable clays and layers mix
54
inceptisols
young soils, poorly formed layering and weathering
55
aridosols
desert soils, saline or alkaline soils
56
mollisols
calcium rich soils high in humus
57
spodosols
light gray, leached A horizon, organic material carried to B horizon
58
alfisols
acid soils with clay rich subsoils
59
ultisols
more weathered alfisols
60
oxisols
intensely weathered and leached soils
61
histosols
wetland soils
62
andisols
volcanic ash soils
63
gelisols
permafrost soils
64
A horizon
upper layer (zone of leaching); ranges from topsoil to bottom of root zone, generally rich in organic material (humus) rainwater dissolves minerals (leaching)
65
B horizon
zone of deposition; little organic matter, dissolved minerals from A-horizon may precipitate (Fe and Al oxides, calcite), often contains weathered rock fragments
66
C horizon
weathered rock
67
soil layers are not always
alphabetical (e.g., R, H, E, O)
68
dry climate's effect on A horizon
thin, mostly unweathered
69
dry climate's effect on B horizon
caliche formation
70
temperate climate's effect on A horizon
thick, rich in humus, mildly weathered
71
temperate climate's effect on B horizon
minor precipitates
72
tropic climate's effect on A horizon
very little humus, highly leached
73
tropic climate's effect on B horizon
insoluble Fe and Al minerals that do not leach
74
best quality soil climate & characteristics
temperate; rich in humus and not highly leached
75
intermediate quality soil climate & characteristics
arid; not highly leached, but poor in humus
76
poor quality soil climate & characteristics
tropical; highly leached
77
how can tropical soils be poor if they support lush jungles
all the nutrients are in the plants, not the soil
78
why do subsistence farmers only grow crops for a few years before the crops start to fail and they have to clear a new plot of land?
the soil is poor and only the dying plants are the source of nutrients for growing plants

Fall 2018 (24 decks)

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