This Week and next

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This Week (and next)

• Today Floods
• Wednesday Groundwater
• Friday Glaciers
• Week from Friday Midterm 2
• Covers through glaciers

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Todays Plan - Floods

• First Current geology events in the news
• Flood frequency
• Flood hazards
• The Biggest Flood Ever
• An even bigger one?

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Whats a flood and how often do rivers do it?

• Flood river leaves its natural channel
• Frequency? Size matters (bigger floods are rarer
  than smaller ones)
• Most rivers will experience some flooding about
  every two years

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Your WarmUp responses Levees

• Natural levees are caused by
• beavers. 1
• trees on the banks of
• rivers and streams. 9
• erosion of flood plains,
• except near stream banks. 43
• the same thing that causes
• deltas (decreased competence). 47

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Levees in the local news
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Levees in the local news
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Levees in the local news
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Levees in the local news
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Levees in the local news
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Quick Quiz

• Would you expect the material in a levee to be
  coarser or finer sediment than the material on
  the adjacent floodplain?

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Flood Frequency

• Flood size-frequency is expressed as 50 year
  flood (or 100 year flood)
• Refers to a flood size that occurs ON AVERAGE
  every 50 (or 100) years
• Such a flood has a 1/50 (or 1/100) chance of
  occurring in any given year
• Could two 50 year floods happen in consecutive
  years?

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Your WarmUp Responses

• A "200-year" flood...

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Flood Frequency-1970s
1-year flood?
1970
1979
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Flood Frequency-1970s
2-year flood?
1970
1979
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Flood Frequency-1980s
1-year flood?
1980
1989
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Flood Frequency-1990s
1-year flood?
1990
1999
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Local Floods Skagit River

• there was flooding in 1990 causing 36,000,000 in
  damages and more floods in 1995-96 that caused
  more damage

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Skagit River west Mt.Vernon, 1975
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Conway, 1951
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Has flooding become worse over time?

• Losses? loss of life or loss of property

Early death rates probably underestimate real
losses
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The biggest flood ever (around here anyway)

• Groups of four
• Count off into A-B-C-D
• Each is responsible for making sure everyone in
  group knows answer to one question

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The biggest flood ever

• How deep was Lake Missoula, and what is the
  geologic evidence for its existence?
• What are three landforms providing evidence of
  the great flood?
• What caused this lake flood, and how many times
  did it happen?
• What was the maximum size mentioned of the
  transported sediment in this flood?

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Go to Video
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Finally, a flood of possibly mythic proportions

• Noahs Flood hypothesis
• William Ryan Walter Pittman (Columbia U.)
• Controversial, not universally accepted, but
  intriguing

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Noahs Flood

• Coming out of last ice age 7600 years ago (5600
  B.C.), sea level was low but rising
• Why?
• Black Sea was fresh water, surrounded by farms

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Bosporus Strait
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Noahs Flood

• Rising global sea level raised Mediterranean
  above the Bosporus Strait
• Broke through natural dam
• Water rose 6 inches / day
• Flooded lakeshore communities

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some Noahs Flood evidence

• Many cultures have a flood story, many can be
  traced to the Black Sea area
• Remains of houses villages have been found on
  the pre-flood lakeshore
• But New work finds no evidence for a sudden
  rise in water level of Black Sea.

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Noahs Flood

• More info
• book Noahs Flood The new scientific
  discoveries about the event that changed
  history, Ryan Pittman, 1998, Simon Schuster