| Title | Composition and origin of an ice-rich mound (lithalsa) in the Great Slave Lowland, Northwest Territories, Canada |
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| Author | Gaanderse, A; Wolfe, S ; Burn, C |
| Source | Proceedings of GeoQuébec 2015, 68th Canadian Geotechnical Conference and 7th Canadian Permafrost Conference; 2015 p. 230 |
| Year | 2015 |
| Alt Series | Earth Sciences Sector, Contribution Series 20150330 |
| Publisher | Canadian Geotechnical Society |
| Meeting | GeoQuébec 2015, 68th Canadian Geotechnical Conference and 7th Canadian Permafrost Conference; Quebec City; CA; September 20-23, 2015 |
| Document | book |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Northwest Territories |
| NTS | 85J/10 |
| Area | Yellowknife; Boundary Creek; Great Slave Lake |
| Lat/Long WENS | -115.0000 -114.9167 62.5500 62.5000 |
| Subjects | surficial geology/geomorphology; Nature and Environment; ice; ice conditions; till mounds; deglaciation; glacial history; Great Slave Lowlands; Cenozoic; Quaternary |
| Program | Climate Change Geoscience Land-based Infrastructure |
| Released | 2015 01 01 |
| Abstract | Recent recognition of raised mounds in the widespread discontinuous permafrost zone of the Great Slave Lowland, NWT, has prompted questions regarding their internal composition and development. To
answer these, fieldwork was undertaken in the summers of 2011 and 2012 at the Boundary Creek Study Area (BCSA, 62° 32'N; 114° 58'W), 30 km west of Yellowknife. This region was deglaciated at about 13 cal kyr BP, after which fine-grained
glaciolacustrine sediments were deposited across the lowlands by Glacial Lake McConnell, and subsequently washed into topographic lows between bedrock highs during lake level recession. At BCSA, a prominent mound 700 m long and 4 m high occurs
adjacent to a peatland and, from the results of this investigation, is identified as a lithalsa.
Borehole drilling parallel to the short axis of the lithalsa revealed ice-poor conditions within the first 4 m of substrate, with substantial
increases in ice content at greater depths within underlying clays. The lithalsa core is composed of layered ice lenses on the order of 0.1 m thick. Stratigraphic records indicate that the sequence of clays, silts and sands are sub-parallel but
domed, in accordance with the surficial relief of the lithalsa. Estimated differential heave between the lithalsa and the adjacent peatland is approximately 2.8 m, of which 2.17 m may be directly accounted for by ice lenses within the first 8.4 m of
sediment. The ?18O values between -18.4 and -16.6 ‰ from ice lenses at depth indicate that the layered ice core formed from modern meteoric waters. The groundwater source is likely from a talik associated with a pond flanking the north side of the
lithalsa. A basal peat sample in the peatland indicates terrestrial exposure at approximately 1200 cal yr BP. Within the lithalsa, a detrital organic sample dating to 700 cal yr BP was collected below 3 m of sediment, whereas a 400 cal yr BP sample
was recovered under a small peat pocket on top of the lithalsa. These results suggest terrestrial exposure and subsequent permafrost aggradation between 700 and 400 cal yr BP.
The mound at BCSA meets the main criteria for lithalsa formation: a
warm ground thermal regime (approximately -1°C) to support water migration to ice lenses, an abundant water supply to feed the ice lenses via cryosuction, and the presence of fine-grained sediment promoting ice segregation and unfrozen water contents
at depth. |
| Summary | (Plain Language Summary, not published)
Recent recognition of lithalsas in the Great Slave Lowland, NT, prompted a detailed investigation to evaluate the internal composition and geomorphic
origin of one lithalsa. Borehole drilling revealed ice-poor conditions within the first 4 m within the lithalsa, with substantial increases in ice content at greater depths. The lithalsa core is composed of layered ice lenses over 0.1 m thick, formed
of isotopically-modern meteoric waters. The stratigraphic sequence of clays, silts and sands is sub-parallel, but domed in accordance with the surficial relief of the lithalsa. Estimated differential heave between the lithalsa and an adjacent
peatland is approximately 2.8 m, of which 2.17 m is directly accounted for by ice lenses within the first 8.4 m of material. Carbon-14 dating indicates permafrost aggradation within the lithalsa occurred between 700 and 400 cal yr BP. |
| GEOSCAN ID | 297393 |
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