1
Q
What are the main factors that influence weathering rates?
A
Rock properties (surface area, mineralogy, cement), climate (rainfall & temperature), presence of soil, length of exposure, steepness.
2
Q
What is physical weathering?
A
Breakdown of rocks into smaller pieces without chemical change, e.g., freeze-thaw, insolation, salt weathering, wetting and drying, stress release, exfoliation.
3
Q
What is chemical weathering?
A
Decomposition of rocks through chemical reactions such as solution, hydrolysis, and oxidation.
4
Q
What is freeze-thaw weathering?
A
Water enters cracks, freezes, expands, and breaks rock apart.
5
Q
What is insolation weathering?
A
Expansion and contraction of minerals due to temperature changes, leading to cracking.
6
Q
What is salt weathering?
A
Growth of salt crystals in pores and cracks exerts pressure, breaking rocks.
7
Q
What is wetting and drying weathering?
A
Repeated swelling and shrinking weakens rock, common in clay-rich rocks.
8
Q
What is stress-release weathering?
A
Expansion and fracturing of rocks due to unloading or removal of overlying material.
9
Q
What is exfoliation?
A
Peeling of surface layers due to expansion and contraction of rocks.
10
Q
What is hydrolysis?
A
Chemical breakdown of minerals due to reaction with water, e.g., feldspar → clay + ions + dissolved silica.
11
Q
What is oxidation?
A
Reaction of oxygen with minerals, especially iron, producing oxides like hematite or limonite.
12
Q
What is simple solution weathering?
A
Mineral dissolves completely into solution without forming new substances.
13
Q
What is pH?
A
The concentration of hydrogen ions in a solution, indicating acidity or alkalinity.
14
Q
What is the Wentworth scale?
A
A classification scheme for sediment grain size.
15
Q
What is the phi (ϕ) scale?
A
A logarithmic scale for grain size: ϕ = -log2(d), where d is grain diameter in mm.
16
Q
How is grain size measured in the lab?
A
By sieving sediments through nested mesh screens corresponding to mm and phi sizes.
17
Q
What does sorting describe?
A
The variation in grain size within a sample; well-sorted = uniform size, poorly sorted = mixed sizes.
18
Q
What does a steep slope on a cumulative curve mean?
A
Good sorting of grains.
19
Q
What does a gentle slope on a cumulative curve mean?
A
Poor sorting of grains.
20
Q
What is the mode of a grain-size distribution?
A
The most frequently occurring grain size.
21
Q
What is the median grain size?
A
The 50th percentile grain size (midpoint of distribution).
22
Q
What is the mean grain size?
A
The arithmetic average, often estimated from 16th, 50th, and 84th percentiles.
23
Q
What is standard deviation in grain size?
A
A measure of sorting; low = well-sorted, high = poorly sorted.
24
Q
What does skewness in grain size mean?
A
Asymmetry: fine-skewed = excess fines; coarse-skewed = excess coarse particles.
25
What is kurtosis in grain-size distribution?
The sharpness or peakedness of the distribution.
26
Why does grain size matter?
It helps interpret depositional environments, reservoirs, transport processes, and sediment stability.
27
What controls particle shape?
Mineral composition, size, transport process, and distance of transport.
28
Which mineral rounds faster: quartz or limestone?
Limestone rounds faster than quartz.
29
Which process is most effective at rounding grains: wind or river?
Wind is more effective than rivers.
30
What do surface textures reveal?
Clues about depositional environments, e.g., glacial striations, eolian rounding, littoral percussion marks.
31
What is fabric in sedimentary rocks?
Arrangement of grains (orientation and packing), influencing porosity, density, and permeability.
32
What are the main factors that influence weathering rates?
Rock properties (surface area, mineralogy, cement), climate (rainfall & temperature), presence of soil, length of exposure, steepness.
33
What is physical weathering?
Breakdown of rocks into smaller pieces without chemical change, e.g., freeze-thaw, insolation, salt weathering, wetting and drying, stress release, exfoliation.
34
What is chemical weathering?
Decomposition of rocks through chemical reactions such as solution, hydrolysis, and oxidation.
35
What is freeze-thaw weathering?
Water enters cracks, freezes, expands, and breaks rock apart.
36
What is insolation weathering?
Expansion and contraction of minerals due to temperature changes, leading to cracking.
37
What is salt weathering?
Growth of salt crystals in pores and cracks exerts pressure, breaking rocks.
38
What is wetting and drying weathering?
Repeated swelling and shrinking weakens rock, common in clay-rich rocks.
39
What is stress-release weathering?
Expansion and fracturing of rocks due to unloading or removal of overlying material.
40
What is exfoliation?
Peeling of surface layers due to expansion and contraction of rocks.
41
What is hydrolysis?
Chemical breakdown of minerals due to reaction with water, e.g., feldspar → clay + ions + dissolved silica.
42
What is oxidation?
Reaction of oxygen with minerals, especially iron, producing oxides like hematite or limonite.
43
What is simple solution weathering?
Mineral dissolves completely into solution without forming new substances.
44
What is pH?
The concentration of hydrogen ions in a solution, indicating acidity or alkalinity.
45
What is the Wentworth scale?
A classification scheme for sediment grain size.
46
What is the phi (ϕ) scale?
A logarithmic scale for grain size: ϕ = -log2(d), where d is grain diameter in mm.
47
How is grain size measured in the lab?
By sieving sediments through nested mesh screens corresponding to mm and phi sizes.
48
What does sorting describe?
The variation in grain size within a sample; well-sorted = uniform size, poorly sorted = mixed sizes.
49
What does a steep slope on a cumulative curve mean?
Good sorting of grains.
50
What does a gentle slope on a cumulative curve mean?
Poor sorting of grains.
51
What is the mode of a grain-size distribution?
The most frequently occurring grain size.
52
What is the median grain size?
The 50th percentile grain size (midpoint of distribution).
53
What is the mean grain size?
The arithmetic average, often estimated from 16th, 50th, and 84th percentiles.
54
What is standard deviation in grain size?
A measure of sorting; low = well-sorted, high = poorly sorted.
55
What does skewness in grain size mean?
Asymmetry: fine-skewed = excess fines; coarse-skewed = excess coarse particles.
56
What is kurtosis in grain-size distribution?
The sharpness or peakedness of the distribution.
57
Why does grain size matter?
It helps interpret depositional environments, reservoirs, transport processes, and sediment stability.
58
What controls particle shape?
Mineral composition, size, transport process, and distance of transport.
59
Which mineral rounds faster: quartz or limestone?
Limestone rounds faster than quartz.
60
Which process is most effective at rounding grains: wind or river?
Wind is more effective than rivers.
61
What do surface textures reveal?
Clues about depositional environments, e.g., glacial striations, eolian rounding, littoral percussion marks.
62
What is fabric in sedimentary rocks?
Arrangement of grains (orientation and packing), influencing porosity, density, and permeability.
63
What is differential weathering?
When different minerals or rocks weather at different rates due to varying resistance.
64
Why do rocks with high surface area weather faster?
Because more surface is exposed to chemical and physical processes.
65
Which mineral weathers fastest: olivine, feldspar, or quartz?
Olivine weathers fastest, quartz weathers slowest.
66
What role does climate play in weathering?
Warm, wet climates accelerate chemical weathering; cold, dry climates slow it down.
67
What is spheroidal weathering?
Rounding of rock corners and edges due to chemical weathering.
68
How does soil enhance weathering?
Soil retains water and acids, increasing chemical weathering rates.
69
Why does feldspar weather into clay?
Hydrolysis reactions break down feldspar structure, forming clay minerals.
70
What is carbonation in weathering?
Reaction of carbonic acid (H2CO3) with minerals like calcite, dissolving limestone.
71
What is biological weathering?
Breakdown of rock by plants, animals, or microbes (e.g., root wedging, lichen acids).
72
Which weathers faster: basalt or granite?
Basalt weathers faster due to higher content of unstable minerals like olivine and pyroxene.
73
What does well-sorted sand indicate about transport?
Longer or repeated transport, often by wind or water, allowing uniform size selection.
74
What does poorly sorted sediment suggest?
Rapid deposition, e.g., by glaciers, floods, or debris flows.
75
What are imbricated gravels?
Overlapping, tilted clasts that indicate paleoflow direction.
76
What is porosity?
Percentage of pore space in a rock or sediment.
77
What is permeability?
Ability of a rock to transmit fluids through connected pores.
78
How does grain shape affect porosity?
Rounded grains usually pack less efficiently, leading to higher porosity than angular grains.
79
What environment typically produces well-rounded grains?
Wind-blown (eolian) environments.
80
What environment often produces angular grains?
Glacial or alluvial environments, with limited transport.
81
Why do geologists use grain-size distributions?
To interpret depositional environments and transport mechanisms.
82
What does a positively skewed grain-size distribution indicate?
Excess fine particles in the sample.
83
What are the main factors that influence weathering rates?
Rock properties (surface area, mineralogy, cement), climate (rainfall & temperature), presence of soil, length of exposure, steepness.
84
What is physical weathering?
Breakdown of rocks into smaller pieces without chemical change, e.g., freeze-thaw, insolation, salt weathering, wetting and drying, stress release, exfoliation.
85
What is chemical weathering?
Decomposition of rocks through chemical reactions such as solution, hydrolysis, and oxidation.
86
What is freeze-thaw weathering?
Water enters cracks, freezes, expands, and breaks rock apart.
87
What is insolation weathering?
Expansion and contraction of minerals due to temperature changes, leading to cracking.
88
What is salt weathering?
Growth of salt crystals in pores and cracks exerts pressure, breaking rocks.
89
What is wetting and drying weathering?
Repeated swelling and shrinking weakens rock, common in clay-rich rocks.
90
What is stress-release weathering?
Expansion and fracturing of rocks due to unloading or removal of overlying material.
91
What is exfoliation?
Peeling of surface layers due to expansion and contraction of rocks.
92
What is hydrolysis?
Chemical breakdown of minerals due to reaction with water, e.g., feldspar → clay + ions + dissolved silica.
93
What is oxidation?
Reaction of oxygen with minerals, especially iron, producing oxides like hematite or limonite.
94
What is simple solution weathering?
Mineral dissolves completely into solution without forming new substances.
95
What is pH?
The concentration of hydrogen ions in a solution, indicating acidity or alkalinity.
96
What is the Wentworth scale?
A classification scheme for sediment grain size.
97
What is the phi (ϕ) scale?
A logarithmic scale for grain size: ϕ = -log2(d), where d is grain diameter in mm.
98
How is grain size measured in the lab?
By sieving sediments through nested mesh screens corresponding to mm and phi sizes.
99
What does sorting describe?
The variation in grain size within a sample; well-sorted = uniform size, poorly sorted = mixed sizes.
100
What does a steep slope on a cumulative curve mean?
Good sorting of grains.
101
What does a gentle slope on a cumulative curve mean?
Poor sorting of grains.
102
What is the mode of a grain-size distribution?
The most frequently occurring grain size.
103
What is the median grain size?
The 50th percentile grain size (midpoint of distribution).
104
What is the mean grain size?
The arithmetic average, often estimated from 16th, 50th, and 84th percentiles.
105
What is standard deviation in grain size?
A measure of sorting; low = well-sorted, high = poorly sorted.
106
What does skewness in grain size mean?
Asymmetry: fine-skewed = excess fines; coarse-skewed = excess coarse particles.
107
What is kurtosis in grain-size distribution?
The sharpness or peakedness of the distribution.
108
Why does grain size matter?
It helps interpret depositional environments, reservoirs, transport processes, and sediment stability.
109
What controls particle shape?
Mineral composition, size, transport process, and distance of transport.
110
Which mineral rounds faster: quartz or limestone?
Limestone rounds faster than quartz.
111
Which process is most effective at rounding grains: wind or river?
Wind is more effective than rivers.
112
What do surface textures reveal?
Clues about depositional environments, e.g., glacial striations, eolian rounding, littoral percussion marks.
113
What is fabric in sedimentary rocks?
Arrangement of grains (orientation and packing), influencing porosity, density, and permeability.
114
What is differential weathering?
When different minerals or rocks weather at different rates due to varying resistance.
115
Why do rocks with high surface area weather faster?
Because more surface is exposed to chemical and physical processes.
116
Which mineral weathers fastest: olivine, feldspar, or quartz?
Olivine weathers fastest, quartz weathers slowest.
117
What role does climate play in weathering?
Warm, wet climates accelerate chemical weathering; cold, dry climates slow it down.
118
What is spheroidal weathering?
Rounding of rock corners and edges due to chemical weathering.
119
How does soil enhance weathering?
Soil retains water and acids, increasing chemical weathering rates.
120
Why does feldspar weather into clay?
Hydrolysis reactions break down feldspar structure, forming clay minerals.
121
What is carbonation in weathering?
Reaction of carbonic acid (H2CO3) with minerals like calcite, dissolving limestone.
122
What is biological weathering?
Breakdown of rock by plants, animals, or microbes (e.g., root wedging, lichen acids).
123
Which weathers faster: basalt or granite?
Basalt weathers faster due to higher content of unstable minerals like olivine and pyroxene.
124
What does well-sorted sand indicate about transport?
Longer or repeated transport, often by wind or water, allowing uniform size selection.
125
What does poorly sorted sediment suggest?
Rapid deposition, e.g., by glaciers, floods, or debris flows.
126
What are imbricated gravels?
Overlapping, tilted clasts that indicate paleoflow direction.
127
What is porosity?
Percentage of pore space in a rock or sediment.
128
What is permeability?
Ability of a rock to transmit fluids through connected pores.
129
How does grain shape affect porosity?
Rounded grains usually pack less efficiently, leading to higher porosity than angular grains.
130
What environment typically produces well-rounded grains?
Wind-blown (eolian) environments.
131
What environment often produces angular grains?
Glacial or alluvial environments, with limited transport.
132
Why do geologists use grain-size distributions?
To interpret depositional environments and transport mechanisms.
133
What does a positively skewed grain-size distribution indicate?
Excess fine particles in the sample.
134
What is fluid density?
Mass per unit fluid volume (e.g., water = 0.998 g/mL at 20°C).
135
What is viscosity?
A measure of a fluid's resistance to flow. Low viscosity = flows easily (air, water). High viscosity = sluggish flow (ice, honey).
136
What is laminar flow?
Flow with straight, coherent streamlines, occurring at low velocities and over smooth beds.
137
What is turbulent flow?
Flow with irregular, random motion, occurring at higher velocities and lower viscosities (most water and air flows).
138
What does Reynolds number predict?
It predicts whether flow will be laminar or turbulent based on inertial vs. viscous forces.
139
What conditions lead to laminar flow?
Low Reynolds number, high viscosity, low velocity, usually shallow depths.
140
What conditions lead to turbulent flow?
High Reynolds number, high inertial forces, high velocity.
141
What is the critical Reynolds number for flow transition?
Approximately 500–2000, depending on boundary conditions.
142
What is the boundary layer?
The region adjacent to a boundary (e.g., streambed) where friction reduces velocity.
143
What is the viscous sublayer?
The layer at the boundary dominated by molecular viscous forces where flow is nearly zero.
144
What is the Froude number (Fr)?
The ratio of inertial to gravitational forces, used to define flow state and bedforms.
145
What does Fr < 1 indicate?
Subcritical (tranquil) flow; waves travel upstream against current.
146
What does Fr > 1 indicate?
Supercritical (rapid) flow; used to define bedforms like ripples.
147
What are the three main steps of particle transport by fluids?
1. Erosion and entrainment, 2. Transport, 3. Deposition.
148
What is the critical threshold in sediment transport?
The point at which grains begin to move due to boundary shear stress and flow velocity.
149
What forces must overcome gravity and friction for grains to move?
Drag and lift forces.
150
What is the Bernoulli effect in sediment transport?
Convergence of streamlines increases velocity, lowers pressure, and allows hydrostatic pressure to lift particles.
151
What does the Hjulström diagram show?
The relationship between grain size and the velocity required to erode, transport, and deposit particles.
152
Why do very fine particles (<0.05 mm) require higher velocity to entrain?
Because of cohesive forces between particles.
153
What does the Shields diagram describe?
The relationship between shear stress, grain size, and initiation of motion.
154
What is terminal fall velocity?
The steady settling rate of a particle when drag and lift balance gravity.
155
What does Stokes’ Law predict?
The settling velocity of small particles (<0.1–0.2 mm) in a fluid.
156
When does material remain in suspension?
When shear velocity (U*) is greater than settling velocity (V).
157
How does wind transport sediment?
By entraining fine particles, often propagating movement by grain impacts; usually fine sand or smaller.
158
What is a dust load?
Suspended fine particles carried long distances by wind, e.g., deep-sea pelagic sediments.
159
How does ice transport sediment?
By plucking and scraping, entraining large volumes due to its high viscosity and laminar flow.
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