T291 The Legacy of Herbert E. Wright, Jr.: Seminal Contributions toward Understanding Interactions among Quaternary Climate, Landscape Processes, Vegetation, and Human Society

Wednesday, 28 September 2016
8:00 AM - 12:00 PM
Room 407

A HOLOCENE GLACIOLACUSTRINE RECORD OF THE LYMAN GLACIER AND IMPLICATIONS FOR GLACIER FLUCTUATIONS IN THE NORTH CASCADES, WA

Paper number: T291-12
Program: Technical Sessions
Time: 10:40 AM – 10:55 AM

Authors

Abstract

The Holocene glacial history of the North Cascades is poorly understood, in part because most existing records rely on moraine remnants and are therefore discontinuous. To develop a more complete record of Holocene fluctuations of North Cascades glaciers, we collected and analyzed glaciolacustrine sediments (i.e., rock flour) deposited over the past ~7800 years in Lyman Lake by the upstream Lyman Glacier. We combined these results with equilibrium-line altitude reconstructions and glacier-climate modeling to quantify the climatic conditions that drove these fluctuations. Finally, we compared the Lyman Glacier’s continuous fluctuation record to existing glacier and climate records of the North Cascades. The Lyman Glacier's fluctuation history follows:

Time Period (cal yr BP)

Glacier Extent

7800 – 4900

No glacier

4900 – 4200

Intermediate

4200 – 3800

Minimum

3760 – 2900

Unsure

2900 – 2600

None

2600 – 2500

Min.

2500 – 2250

Int.

2250 – 2100

Unsure

2100 – 2000

None

2000 – 1800

Unsure

1800 – 1300

Int.

1300 – 1200

Min.

1200 – 1100

Unsure

1100 – 900

Int.

900 – 800

Minimum

800 – 600

Int.

600 – 500

Maximum

500 – 350

Int.

350 – 150

None

150 – 50

Max.

50 – Present

Min.

Our analysis indicates that: 1) the earliest Neoglacial advances in the region (starting ~6 ka) occurred asynchronously, with higher latitude and more maritime sites experiencing earlier advances; 2) Neoglacial advances remained small, infrequent and asynchronous until the last millennium; 3) Beginning at ~1.0 ka, glaciers throughout the North Cascades advanced synchronously, signaling the onset of the Little Ice Age (LIA); 4) North Cascades glaciers reached their maximum Holocene extents during the 15th and early 16th centuries (~0.55 – 0.45 ka), followed by apparent regional retreat and a final smaller 19th century (~0.15 – 0.05 ka) re-advance. The asynchronous early-to-mid Neoglacial fluctuations followed by synchronous LIA behavior suggests that local climate factors drove glacier fluctuations until the regional climate signal became strong enough to induce synchrony ca. 1.0 ka. Although the inferred regional retreat remains uncertain, the disappearance of the Lyman Glacier in the mid-LIA (~0.45 – 0.15 ka) is consistent with the precipitation record at Castor Lake (~100 km to the east), which indicates unusually dry winter conditions between ~1450 – 1850 CE (~0.5 – 0.1 ka).

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-277539

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.