Drumlins Along The Potomac

1
Drumlins Along The Potomac
The case for Alpine Glaciation In the Potomac
River Valley By Douglas L. Love
2
The Potomac makes several incised bends near
Sharpsburg, MD.
3
Basemap of the study area at 124,000
4
(No Transcript)
5
Snyders Landing Cave 2, my interest in the area
6
The 2 caves brought me to visit this area.
7
Speleothems in Snyders Landing Caves

• Flowstone Curtains

Stalagmites
Stalactites
8
Life in Snyders Landing Caves

• Indiana Cave Salamanders

Bird nests near entrance
Common Black Salamanders
Cave Spiders
Cave Crickets
9
A Hanging Valley, one of several along the
Potomac west of Snyders Landing
10

• On top of a hanging valley looking down

11

• Behind the hanging valleys are deep sinks!

12
The downslope of most valleys in this hillside
were cut away to build the CO Canal.
13
Streams produce v-shaped valleys.
14
One of the few v-shaped valleys west of Snyders
landing.
15
But the valleys on top of this hill are flat,
u-shaped, with frequent steep headwalls. I
believe that these are Cirques from alpine
glaciation!
16

• Alpine Glaciers many miles from the ice sheet
• can be seen in this Landsat image of eastern
  Greenland

17

• These cirques are some places en-echelon,
• With one leading to another below it.

18
The soil is dark and thin in these valleys, and
frequently rounded, striated pebbles can be
found near the surface.
19
One series of cirques ends at this flat-floored
sink, near Snyders Landing Cave 1
20
Jagged boulders ring the col above the cirques
leading to the sink.
21
In the meadow on top of the hill, the bedrock
also shows striations.
22
Not everything is glacial. These cobbles were
piled here to dam the valley.
23
Even on the south side of the neck, the valley
remains U-shaped below the dam.
24

• Black earth resembling glacial till can be found
  in the flat valleys.

25

• Just below a flat valley leading to one of the
  slot canyons, black and brown earth are found
  together

26

• Not all of the slot valleys show glacial
  indicators.
• Here are non-rounded boulders in brown forest
  soil that was originally laid down by the Potomac
  when it was at this level.
• Other rounded boulders seem to have been Potomac
  rapids.

27

• Areas of observed glacial features

28
The Geologic Map of the CO Canal shows Terrace
Deposits on top of the hill.
29
Points for and against Glaciation on the Potomac

• No glaciation known in this area.
• It could be all karst.
• Hills were modified by creation of CO Canal
• These are mapped as Strath Terraces

• Lots of Cirques
• Striations on rocks
• Karst modified by glaciation. Sinks are plugged,
  caves are mostly dry.
• Their glacial nature may have been overlooked.

Recent pictue of Benjamin Blair by a suspected
Rouche Mouton
30
Future work

• Map the locations of these cirques
• Find more on other necks and elsewhere nearby
• Find more evidence of glaciation
• Explain how glaciers could exist here south of
  the ice sheet margin
• Date them. They look very recent, based on size
  of trees! This area mustve been lumbered.

A group stands across the width of the second
Col above the V-shaped valley.
31
Whats it good for?

• A publishable paper?
• A PhD thesis?
• Get into an argument with the experts?
• Prove something not known before?
• An excuse to hike

Ice on the hillside below the cirques, March 2005.
Maybe all of the above.