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Natural Disasters Earth Sc 2GG3 > Lecture 6: Subsidence > Flashcards

Lecture 6: Subsidence Flashcards

1
Q

Subsidence

A

-near vertical downward movement of Earth’s surface

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2
Q

Karst

A

-irregular landscape containing a lot of depressions

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3
Q

Types of Sinkholes

A

1) Solution Sinkhole:formed by acidic groundwater

2) Collapse Sinkholes: formed by collapse at surface

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4
Q

Ground Water Table

A

AKA Water table, the underground depth at which the ground is saturated with water

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5
Q

Flow Stone

A

General term for accumulation of Calcium Carbonate precipitated from water in a cave

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6
Q

Stalactite

A

deposit of Calcium Carbonate that extends downwards from the roof

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7
Q

Stalagmite

A

deposit of Calcium Carbonate on floor of cave

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8
Q

Column

A

feature formed when stalactite and stalagmite join together

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9
Q

Tower Karst

A

Large rock pillars are remnants of a highly eroded landscape

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10
Q

Disappearing Streams

A

stream that disappears into a cave

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11
Q

Springs

A

Area where groundwater discharges at the surface

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12
Q

Permafrost

A

Areas with annual mean temperature lower then 0 deg. celcius

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13
Q

Fine Sediment

A
  • land compacts with low water in pores of soil

- balanced by sediment deposited from rivers

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14
Q

Collapsible Sediment

A

Soil has large amount of pore space; large amounts of water can dissolve minerals that hold soil together, and can collapse

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15
Q

Organic Sediments

A

soils contains much water; water decrease results in thickness decreasing

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16
Q

Expansive Soils

A
  • easily expand/contract with we/dry periods

- dessication cracks can be left behind in clay rich areas

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17
Q

Effects of Subsidence

A

1) Sinkhole Formation
2) Groundwater Contamination
3) Permafrost Thaw
4) Changes in Soil Volume

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18
Q

Links of Subsidence to Other Natural Hazards

A
  • flooding in areas of much subsidence

- permafrost or change in soil volume -> landslides

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19
Q

Natural Service Functions of Subsidence

A
  • good drinking water from karst
  • tourism in caves
  • unique creatures in these landscapes
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20
Q

Human Interactions that Increase Subsidence

A

1) Mining Groundwater
2) Underground mining of coal/salt
3) Constructing buildings on permafrost land
4) Levees along rivers
5) Poor landscaping with expansive soils

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21
Q

Minimizing Risk of Subsidence

A
  • pipelines above ground in permafrost areas
  • test soil before building
  • limit levees in less populated areas
  • Use fill layer between building and expansive soils
  • adjust to karst by knowing soil types and where risk is worse
22
Q

Rivers

A

Carry water on land to oceans

-runoff, which is water that does not infiltrate soil, reaches streams is not evaporated

23
Q

Drainage Basin

A

Area of surrounding lake that drains into that rive/lake

24
Q

Divides

A

-Areas of higher land that seperates which way rivers flow

25
Q

Continental Divde

A

-spine of rocky mountains that separate which ocean rivers flow into

26
Q

River Gradient

A

Determined by calculating the change in elevation over the distance the river flows

27
Q

Base Level

A

Where river empties into ocean/lake

28
Q

Bed Load

A

materials that roll, slide, bounce along bottom of river; sand, pebbles

29
Q

Suspended Load

A

silt/clay particles, 90% of total load

30
Q

Dissolved Load

A

Derived from chemical weathering of rock in drainage basin

31
Q

Discharge

A

Volume of water flowing past a point at certain time: Q=VA, Q= Discharge, V= Velocity, A=Area

32
Q

Alluvial Fan

A

deposition of sediment from river onto land

33
Q

Delta

A

deposition of sediment into water

34
Q

Braided Channel

A
  • large number of channels that are wide/shallow
  • islands between made of sand/gravel, no vegetation
  • abundant bed load from melting glaciers
35
Q

Anastomosing Channel

A

2 or more channels with intervening islands

-Islands store temporary sediment, made of silt/clay with vegetation

36
Q

Meandering Channel

A

single snake-like channel

  • velocity of water greatest on outside[erosion], smallest on inside[deposition]
  • meanders get larger and river lengthens
37
Q

Floodplain

A

area of land adjacent to channel that is subject to flooding

38
Q

Avulsion

A

-during a flood, water abandons the big loop and cuts an easier route, forming an ox-bow lake

39
Q

Meander Scar

A

-dried up ox-bow lake

40
Q

What does Magnitude/duration of flood depend on?

A

1) Precipitation in drainage basin
2) Rate at which precipitation infiltrates soil
3) Pressence of Snowpack
4) Amount of Moisture in soil
5) Speed of surface runoff in water
5) Ice Jams in river

41
Q

Stage

A

Level of the river surface

42
Q

Flood Stage

A

Level river surface must reach to cause property damage

43
Q

Hydrograph

A

Graph that shows change in discharge/stage over time

44
Q

Recurrence Interval

A

Average time between floods of certain size

45
Q

Upstream Floods

A

-occur in upper part of drainage Basin
-produced by large amount of rainfall in small area
-occur in steep areas with little vegetation
ie: Flash Flood:
Sudden flood that causes a large amount in discharge

46
Q

Downstream Floods

A
  • produced by rain of long duration in large areas
  • slow but substantial increase in discharge
  • ie: Outburst Flood:
  • sudden draining of lakes originally dammed by glacier or other material
47
Q

Why Does Red River Flood so much

A

1) flows South to North
2) Impermeable Soil
3) North has been rising due to melting ice sheet= slower current

48
Q

Links of Floods to Other Natural Hazards

A

landslides/Hurricanes/Volcanoes -> Floods

-floods -> fires/landslides through erosion

49
Q

Natural Service Functions of Floods

A
  • Floodplains are very fertile due to nutrient deposits
  • floods clean debris from channels, help aquatic ecosystems
  • sustain wetlands
50
Q

Human Interactions with Floods

A

Dams: cause deposition upstream of dam, erosion downstream
Urbanization: increase magnitude/freq of floods, because ground is impenetrable and sewers bring water to rivers fast

51
Q

Minimizing Floods

A

Physical Barriers: earthen/concrete levees, floodways, stormwater retention basins
Channelization: Straightening, deepening, widening existing channels

Natural Disasters Earth Sc 2GG3 (6 decks)

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