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EAS > Lecture 19 > Flashcards

Lecture 19 Flashcards

1
Q

Quantifying reoccurrence/risk interval of a flood

A
  • prediction essential
  • plot frequency of last floods
  • calculate reoccurrence interval (average time interval between two floods of the same magnitude)
  • real time monitoring
  • mapping and assessing flood hazard risks
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2
Q

Lakes

A

Standing bodies of water filling depressions on land

In general, an obstacle to flow is necessary to produce a lake

Over time the obstacle tends to be eroded; most lakes are geologically short lived

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3
Q

Causes of lakes

A
  • Glacial erosion and deposition
  • volcanic activity
  • tectonism
  • deposition and erosion of sediment by water (e.g. oxbow lake in meandering rivers)
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4
Q

Open lakes

A

Inlet and outlet streams

  • water level tends to stay constant in short term
  • sediments are typically muds, with sand near shore
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5
Q

Closed lakes

A
  • no stream outlet
  • water levels fluctuate due to evaporation
  • sediments typically include salt deposits formed by evaporation
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6
Q

Oceans

A

Cover 71% of earth’s surface

Uneven distribution in northern (53%) and southern (88%) hemispheres

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7
Q

Distribution of ocean water:depth

A

-average depth 4.5 km
-max depth 11 km
-volume of ocean water 1.35 x 10^18 m^3
(Varies over time-amount of ice)

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8
Q

Salinity

A

Totally salinity (proportion of dissolved ions) is ~3.5% or 35%o (parts per thousand)

Chlorine and sodium make up 80%, rest is trace ions

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9
Q

Dissolved ions

A
  • sodium
  • chloride
  • sulphate
  • magnesium
  • calcium
  • bicarbonate
  • potassium
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10
Q

Distribution of salinity

A
  • salinity is high where evaporation is high (equator)

- salinity is low where river water enters ocean

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11
Q

Temperature variation

A

Temperatures highest in Tropical pacific and Indian oceans, decreases poleward

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12
Q

Temperature and salinity variation with depth

A

-cold water is denser so it sinks
Thermocline: zone of rapid temp change

-saline water is denser so it sinks
Halocline: region of rapid salinity change

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13
Q

Forces driving ocean currents

A
  • air currents (wind on surface)
  • sinking of denser (colder or saline) water
  • effects resulting from rotation of the earth
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14
Q

Ocean surface circulation

A
  • surface circulation is dominated by coriolis driven gyres
  • major westward drift at equator
  • eastward circulation in southern ocean, N.Atlantic, N.Pacific
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15
Q

Thermohaline currents

A

-high salinity descending currents
AABW Antarctic bottom water
NADW North Atlantic deep water

-north flowing surface currents

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16
Q

Coriolis effect

A
  • surface of solid earth is rotating about vertical axis (except at equator)
  • CCW in North hemisphere
  • CW in southern
  • objects moving in a straight line curve
  • right in northern hemisphere
  • left in Southern Hemisphere
17
Q

Ekman transport

A
  • because of Coriolis effect, wind driven current in northern hemisphere is slightly CW of actual wind direction
  • deeper currents are progressively rotated CW
  • in Northern hemisphere, overall average water movement is 90 degrees CW of wind direction
  • no deflection at equator
18
Q

Ekman transport, upwelling and downwelling

A

Upwelling where ekman transport is offshore (brings nutrients to shore)

Downwelling where ekman transport is onshore

19
Q

Tides

A
  • moons gravity on near side is stronger than necessary to maintain orbit, pulling water towards moon
  • moons gravity on far side is weaker, allowing water to spin away from earth
  • hydrosphere is pulled into an elliptical shape
20
Q

Spring tides

A

Sun also causes tides but not as effective as moon

When sun and moon are in line:

  • effects are combined
  • high tidal range
  • high high tides
  • low low tides
21
Q

Neap tides

A
  • when sun and moon are at 90 degrees
  • low tidal range
  • low high tides
  • high low tides
22
Q

Changes in relative sea level

A

Submergence or emergence

These changes results from a combination of

  • worldwide sea level change
  • local effects
23
Q

Eustatic (worldwide change)

A

Changes in ice volume (glaciation / deglaciation)

Changes in volume of ocean basins (volume of mid ocean ridge system)

24
Q

Local changes

A
  • tectonic movements in active areas
  • isostatic response to ice caps and ice sheets
  • compaction of sediment

EAS (19 decks)

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