The Evolution of Glacial Lakes in the Winooski River Valley, Vermont

Stephen Wright Department of Geology University of Vermont

Lake Evolution Outburst Flood Events Timing Isostatic Tilt of Winooski River Basin

1 Lamoille River

Burlington

Winooski River

2 Merwin, 1908

3 Larsen, 1972, 1987

4 Mad River Valley Dog River Valley

Steven’s Branch Valley

308 m 279 m

430 m

5 Lake Roxbury Lake Granville Lake Williamstown

308 m 279 m

Green Mountains

Northfield Mountains

430 m

Branch Branch

st

nd

1 2

White River White River

River White

6 Early Stage of Glacial Lake Winooski

Montpelier

Green Mountains

279 m

Northfield Mountains

7 Maximum extent of Glacial Lake Winooski in the Winooski and Lamoille River Valleys

• Glacial Lake Winooski existed as long as the Winooski River Valley was dammed.

• Rapid northward growth of Glacial Lake Winooski east of the mountains indicates how quickly the ice sheet was retreating east of the mountains compared to ice in the Champlain Valley.

Glacial Lake Vermont

8 Measured Varve Sections Waterbury Three good measured varve sections Reservoir • • Timing of Glacial Lake Winooski • Varve sections correlated to the North American Varve Chronology • Ice-Proximal varves deposited at Muzzy Brook ~14,100 years BP Wrightsville • Glacial Lake Winooski partially drains ~13,820 Reservoir Winooski River years BP • Lake duration ~280 years • Ice Sheet Retreat Rate • Muzzy Brook to Wrightsville Reservoir • 11,700 m/132 years • ~89 m/year • Ice Sheet Retreat Rate • Muzzy Brook to Waterbury Reservoir Muzzy • ~125 years Brook • Conclusion • Wrightsville and Waterbury Reservoirs deglaciated at about the same time • The ice sheet east of the mountains retreated rapidly northward up these tributary valleys

9 Measured Section

10 Correlation of Waterbury Reservoir Varves with the North American Varve Chronology WEST WATERBURY RESERVOIR SECTION EAST

1050 Elevation Glacial Lake Winooski

700

Elevation Glacial Lake Mansfield Waterbury Reservoir 680 Varve Thickness

660

640 Old Little River Alluvium

Thickly-bedded fine to medium-coarse sand with silt interbeds deposited in Glacial Lake Mansfield 620

Water level drop from Lake Winooski to Lake Mansfield Varved silt/clay deposited in Glacial Lake Winooski 600

Normal Reservoir Level Antevs’ The abrupt transition Varve from varved silt/clay to 580 Ice-proximal thickly bedded Thickness fine/very fine sand with thick bedded sand marks silt interbeds

a major water level drop: Reduced 560 the end of Glacial Lake Reservoir Level Winooski 13,820 years BP

540 feet

Varve Thickness (cm) Figure 13: Correlation of varved silt/clay section from the Waterbury Reservoir with Antevs’ (1928) com- piled section for the upper Winooski River valley. Antevs’ original “New England Varve Chronology” has been modified by Ridge (2011) and those numbers reorganized into the “North American Varve Chronology.” The thicknesses used in Antevs’ curve have been normalized. To offset the two curves, 10 cm has been added to the measured thickness of varves in the Waterbury Reservoir section. Thick unit at base of section is a slumped layer. Thick units at the top of the section reflect the draining of Glacial Lake Winooski and the onset of sedimentation in Glacial Lake Mansfield. Based on this correlation Glacial Lake Winooski first formed in this region shortly before 14,020 years ago, lasted for ~200 years, and then catastrophically lowered, forming Glacial Lake Mansfield,13,820 years ago. 11 Glacial Lake Winooski partially Drained when ice sheet retreat uncovered a lower outlet: Gillette Pond.

Gillette Pond Glacial Lake Winooski Outlet

Glacial Lake Vermont

12 Drainage through the new outlet dropped the lake elevation by ~90 m forming Glacial Lake Extent of Glacial Lake Mansfield 1 Mansfield 1 superimposed over the outline of Glacial Lake Winooski.

13 Gillette Pond Outlet

Huntington River Valley

Remnant outlet channel and delta produced when Glacial Lake Winooski drained into the lake occupying the Huntington River Valley.

14 Flood Volume Estimate

• Volume of Glacial Lake Winooski Ice-Dam Failure Mode • 1,206 km3

(1) Subaerial Breach • Volume of Glacial Lake Mansfield 1

• 829 km3 Ice • Flood Volume (3) Flotation of Ice Margin Bedrock • 377 km3

(2) Subglacial Tunnel

15 Transition from Glacial Lake Mansfield 1 to Glacial Lake Mansfield 2 Glacial Lake Mansfield 1

Relatively little additional retreat of the ice sheet uncovers a lower outlet through the Huntington River Valley.

Lake level drops another 26 m.

16 Glacial Lake Mansfield 2

17 Glacial Lake Mansfield 2

18 19 South Hinesburg Delta

Glacial Lake Vermont Hollow Brook Outlet

20 Transition from Glacial Lake Mansfield 2 to Glacial Lake Vermont

Glacial Lake Mansfield 2

Glacial Lake Vermont (Coveville Stage)

21 Williston Village

Winooski River Valley

Williston Outlet Channel

22 Coveville Stage of Glacial Lake Vermont

23 Isostatic Tilt of Deltas Glacial Lake Winooski

• Preliminary best-fit plane based on 11 LiDAR- derived delta elevations and outlet elevation.

• 1.15 m/km to N17W (343)

• 0.90 m/km to N21.5W (Koteff and Larsen, 1989) Glacial Lake Hitchcock

• 1.2 m/km to N19 W (Parent and Occhietti, 1999) Glacial Lakes Memphremagog and Candona

• 0.7 m/km (Rayburn, 2004) Glacial Lake Glacial Vermont Lake Vermont

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