Ice Sheet Melt, St. Lawrence Ice Dams, Mega-Lakes, Carolina Bays, Younger Dryas, and AMOC Collapse.

26–20 ka BP — Ice Sheet at Its Peak

Laurentide Ice Sheet dominates Hudson Bay.

Ice streams carve deep troughs and proto–Great Lakes.

Sea level ~120 m lower, exposing shelves for later floods.

Evidence: Laurentian Channel, ice-stream bedforms.

20–17 ka BP — Ice Retreat & Lake Building

Southern ice margin melts, forming massive lakes (Agassiz, Iroquois).

Water gets trapped → unstable lake levels.

Subglacial floods carve channels, deposit sediments.

Evidence: tunnel channels, varved sediments, old shorelines.

17–15 ka BP — Ice Dams & Spillovers

St. Lawrence blocked repeatedly → lakes rise until dams break.

Overflow cuts new channels (Chicago, Michigan, east).

Evidence: thick sediment layers, delta terraces.

14.65 ka BP — Meltwater Pulse 1A

Global sea level jumps fast, dumping huge freshwater into oceans.

Can slow or collapse North Atlantic circulation.

Evidence: coral terraces, oxygen isotopes.

14.6–13.3 ka BP — Big Ice-Dam Failures

Lake Agassiz extremely high → catastrophic floods.

Floods carve cross-shelf troughs, send sediments offshore.

Evidence: Agassiz layers, turbidites, shelf channels.

Same Time — Backed-Up Floods Inland

Rising Atlantic slows coastal outlets → water reroutes to Mississippi, Ohio, Appalachian rivers.

Big basins flood, leaving slackwater deposits.

Evidence: paleochannels, fine sediments, inland turbidites.

13.3–12.9 ka BP — Flood Maximum

Lake Agassiz hits largest size.

St. Lawrence openings release massive pulses → offshore turbidites.

Evidence: graded sediments, isotope shifts.

12.9 ka BP — Younger Dryas Begins

Freshwater pulses + meltwater trigger AMOC collapse.

Sudden cooling 5–15 °C, wetlands and megafauna affected.

Evidence: black mat layers, isotopes, ecological changes.

12.9–11.7 ka BP — Outlets Reorganize

Ice retreats, northern outlets stabilize.

Great Lakes drainage shifts north; interior flooding decreases.

Evidence: uplifted shorelines, abandoned channels, varve counts.

12.9–11.7 ka BP — Red Sea Lowstand & Reflooding

Red Sea isolates → hypersaline.

Melt pulses reconnect it → rapid regional floods.

Evidence: bathymetry, salinity proxies.

11.7 ka BP — End of Younger Dryas

AMOC restarts → warming.

Champlain Sea forms over parts of St. Lawrence.

Evidence: marine shells, rebound-corrected shorelines.

11.5–10 ka BP — Ice Collapse & Outlet Migration

Laurentide collapse accelerates.

Northern outlets rise; old channels get buried.

Evidence: seismic profiles, paleovalleys.

10–8 ka BP — Shelf Drowning

Continental shelves fully flood → modern coasts locked in.

Evidence: drowned shorelines, filled estuaries.

8–7.6 ka BP — Early Holocene Wet Periods

Mega-lakes expand (Caspian, Xinjiang), Sahara green.

Later transitions to modern dry belt.

Evidence: beach ridges, lake cores, pollen records.

7.6–5.6 ka BP — Black Sea Flood

Rising sea overtops Bosporus → rapid flooding of Black Sea basin.

Evidence: submerged settlements, salinity jumps, delta changes.

6–4 ka BP — Late Holocene Stabilization

Carolina Bays, Great Lakes, and other basins settle into modern drainage.

Evidence: terraces, dunes, stable shorelines.

2 ka BP – Today — Preserved Records

Shelf troughs, turbidites, slackwater deposits, black mats, freshwater isotopes remain as evidence of all these events.