Problems on the Path to the Paleo Delta

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Problems on the Path to the Paleo Delta

• A GIS Project by
• Rachel Lomonaco

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Objectives

• To determine the extent of surficial sediment
  packages outside of Johnson, Vermont .
• To examining the relationship between slope
  composition and slope angle.
• To reconstruct a location of a paleo delta along
  the Lamoille River Valley based on sediment
  deposits.
• To determine a paleo lake level based on the
  elevation of the deltaic deposit.

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Methods

• Points exported from an excel sheet consisting
  of GPS points taken by Lomonaco 2006 and
  formatted to fit the DEM from USGS.
• Polygons of Sediment Extent digitized by
  creating new layers in Arc Cat using 3D methods.
• Slope Analysis creation of a polygon layer with
  the use of the raster calculator and conversion
  from raster to vector data. This layer was joined
  to the points layer to form an analysis.
• Paleo Delta Deposits digitizing using 2D
  methods.
• Paleo Lake Level digitizing using a query based
  on percentage of sediment as a function of
  elevation.

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References

• USGS DEM
• VCGI county layer, river layer, etc.
• GPS Points taken by me!
• Stephen Wright
• Online Refs

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Background

• Delta a landform where the mouth of a river
  flows into a body of water building outwards from
  sediment carried by the river and deposited as
  the water current is dissipated.
• Glacial Lake a lake with origins from glacial
  melt and usually has stages based on ice retreat
  and advance constrained to river valleys. Vermont
  has had many!!
• Till unsorted glacial sediment also known as
  glacial drift.

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Deltaic Deposits
Top-set Beds gravel and some coarse
sand Fore-set Beds coarse to fine
sand Bottom-set Beds fine sand to clay and silt
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Extent of Glacial Sediment Packages
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Sediment Packages as a Function of Slope
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• Most deposits exist on slopes under 5 degrees.
• Sand and Till are more abundant than other
  deposits.
• Till has many more deposits constrained to
  shallow slopes but
• also exists in very steep areas like river
  drainages.
• Sand exists fairly constantly throughout slope
  variation, possibly
• due to its cohesion.

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Paleo River Deltaic Deposit
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Paleo Lake Level Based on Deltaic Deposit
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Implications

• These sediments were deposited as a function of
  glacial processes due to the presence of the
  underlying till.
• Gravel, coarse sand, and fine sand exist in
  layers stratagraphically overlying the till
  deposits even though they may not be
  topographically higher.
• The fining of sediment down valley is indicative
  of a regression or decrease in base level.
  Therefore the deposits record a glacial retreat.
• The presence of gravel and not till as the
  top-set bed indicates that this was the last
  event before modern incision of the Lamoille
  River.
• My hypothesis is that the delta was formed by a
  draining event from Glacial Lake Vermont (650ft
  asl) to a lower lake level.