Evidence of glaciation in PA

Extent

·       Glaciation covered northern and northwestern PA, leaving behind a suite of glacial landforms and deposits.

Till Deposits

·      Found in the Pocono Mountains and NW PA; consist of unsorted sediment containing clay to boulders.

Outwash Plains

·       Composed of well-sorted sands and gravels from glacial meltwater streams, common in the Erie region.

Eskers

·       Found near Jacksville, PA — indicate channels of subglacial meltwater.

Niagara rivers and falls

o   Meltwater breached the Niagara Escarpment ~12,000 years ago; continued erosion has caused Niagara Falls to migrate ~1 foot per year.

Lake Maumee

o   The earliest stage of proglacial Lake Erie (~15,000 years ago). Formed when meltwater from retreating ice was dammed by the ice front and moraines near present-day Fort Wayne, Indiana. Grew progressively eastward as ice margin receded. Left shoreline – exposed high in the bluffs south of Lake Erie

Lake Pittsburgh

o   Formed in southwestern Pennsylvania as the ice blocked northward drainage of river systems; lake occupied ancestral valleys of Allegheny and Monongahela Rivers. Age may be late Illinoian glaciations (~140,000), substantially older than the Wisconsinan lakes like Maumee or Lesley.

Lake Lesley

o   Smaller proglacial lake in north-central Pennsylvania (Tioga & Potter Counties), near headwaters of Pine Creek. Formed during Wisconsinan deglaciation (~18,000–15,000 years ago); meltwater was trapped between retreating ice lobes and local topography in headwaters of Pine Creek and Genesee River valleys. Happy Valley (near State College – also flooded). Ice front served as a temporary dam, and surrounding uplands confined lake in valleys. May have drained catastrophically.

Lake Iroquois

o   large glacial lake occupying Ontario basin (~13,000 years ago) when St. Lawrence River outlet was blocked by ice. Higher lake levels & ancient shorelines mark its extent around Finger Lakes & northern PA region.

Stratigraphic Evidence?

Outcrops & sediment cores show transitions from freshwater (Iroquois-type) varved lake clays to marine Champlain Sea silts, then to modern lacustrine deposits, record changing water chemistry & outlets. Glacial erratic and dropstones record these changes.

Shoreline Terraces

Raised beaches (similar to those found for Lake Maumee) are found in NNY, Ontario, and Quebec!

Paleontological Indicators

Marine fossils (whales, mollusks) in Champlain sediments basin rest on freshwater lake deposits, proving Great Lakes system was fresh before marine inundation.

Hydrologic Modeling

  Simulations suggest drainage may also have been catastrophic or rapid, with immense volumes of meltwater draining to Atlantic via St. Lawrence & Hudson valleys. This may have affected North Atlantic thermohaline circulation & may have briefly cooled regional climate.

Periglacial Evidence in Unglaciated Regions of PA?

Even areas south of ice margin (central & southern PA) show signs of cold, tundra-like conditions during glacial maxima:

·       Hickory Run Boulder Field: Classic example of frost-shattered rock accumulation from freeze–thaw activity.

·       Solifluction lobes and colluvial deposits: Evidence of slow downslope movement in permafrost environments.

·       Periglacial slope deposits: Found across uplands, indicating frost heaving and seasonal freeze–thaw dynamics.

·       Polygonal ground & ice-wedge features: Rare but indicative of permafrost processes.

 

Fossil and Paleoecological Evidence?

·       Pleistocene Faunal Assemblages: Fossils found in caves & sediments throughout PA reveal presence of tundra & boreal species during glacial intervals.

·       Valley Forge National Historical Park (Port Kennedy Bone Cave Site):

o   Contains fossils of Pleistocene mammals including dire wolves, saber-toothed cats, short-faced bears, ground sloths, mastodons, camels & giant beavers.

o   Represents a cold-climate fauna adapted to tundra & open forest conditions, between 20,000–11,000 bp.

o   Indicates glacial-period ecosystems dominated by grasslands & boreal forests, supporting large herbivores & predators that migrated from E-W south of ice front.

·       Other Fossil Sites:

o   Frankstown Cave (Blair County) also contains fossil vertebrates from glacial & interglacial periods.

o   Pollen records from lake sediments & bogs show shifts between tundra and spruce-dominated forests (glacial) to oak–hickory forests (interglacial), illustrating dramatic climate oscillations.