The Landscape of Puget Sound: Tectonics and Glaciers

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The Landscape of Puget Sound Tectonics and
Glaciers
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Puget Lowland Landscape Elements
1) Big hole between the mountains
2) Advance outwash plain
4) Flutes
Hood Canal Puget Sound Lk Washington Kent Valley
3) Troughs
E-W cross-section
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1. Big hole between the mountains
2. Advance outwash plain
3. Troughs
4. Flutes
5. Cross-warps

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1. Big hole between the mountains
2. Advance outwash plain
3. Troughs
4. Flutes
5. Cross-warps

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Tectonic setting of the Puget Lowland
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Tectonic setting of the Puget Lowland
Resulting N-S shortening in the Puget Lowland
Subducting ofJuan de Fuca plate
San Andreas fault
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Bedrock Structure through Puget Sound

Seattle fault zone
South
North
Quaternary
Blakely Harbor Fm
Blakeley Fm
km
Eocene
Crescent Fm



Seattle basin
Seattle uplift
Kingston arch
After Johnson et al., 1994
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Topographic expression of the Seattle fault
Bedrock highs
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1. Big hole between the mountains
2. Advance outwash plain
3. Troughs
4. Flutes
5. Cross-warps

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Booth, et al, 2003
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(map ?D Molenaar, 1987)

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K. Troost
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2m
Vashon till at Perkins Lane
Photo by K. Troost
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Advance outwash sand at a gravel pit near Tacoma
Photos by K. Troost
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Outwash in front of a modern advancing glacier
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Puget Lowland Landscape Elements

1. Big hole between the mountains
2. Advance outwash plain
3. Troughs
4. Flutes
5. Cross-warps

2-5 are glacial in origin
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Modern outwash capped by till, Bering glacier
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Till
Outwash
Vashon-age outwash capped by till, Maury Island
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2) Advance outwash fill plain, Puget Lowland
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Bedrock (S of Seattle fault) (Olympic
Mountains)
The Great Lowland Fill
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Puget Lowland Landscape Elements
1) Big hole between the mountains
2) Advance outwash plain
4) Flutes
Hood Canal Puget Sound Lk Washington Kent Valley
3) Troughs
E-W cross-section
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Water flowing into moulin
Flow at snout of Nigardsbreen glacier, Norway
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• Troughs (subglacial channelways)products of
  glacial meltwater

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• Troughs (subglacial channelways)products of
  glacial meltwater

troughs filled in by late-recessional or
postglacial alluvium or mudflows
Ice limit
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Gradients of subglacial water flow

• Troughs (subglacial channelways)products of
  glacial meltwater

troughs filled in by late-recessional or
postglacial alluvium or mudflows
Ice limit
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Subglacial channelway near Granite Falls
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Channelway (Olalla Valley), now occupied by
underfit stream (Olalla Creek)
Puget Sound
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Subglacial drainage
Snoqualmie R.
Tolt R.
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Modern alluvial fan deposition
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1. Big hole between the mountains
2. Advance outwash plain
3. Troughs
4. Flutes
5. Cross-warps

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4) Flutes glacial scour
24 km
DEM from Haugerud, 2001
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Oblique aerial view of flutes around Echo Lake
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1. Big hole between the mountains
2. Advance outwash plain
3. Troughs
4. Flutes
5. Cross-warps

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Landscape element 5 Cross-warps
Image from Seattle-Area Geologic Mapping Project
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Landscape element 5 Cross-warps
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Image from Seattle-Area Geologic Mapping Project
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