Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin
Extensive fields of vegetated, dome‐shaped earth hummocks 5–35 cm high and typically 80–200 cm in diameter occur on slopes of up to 15° at elevations of 320–440 m asl on Dartmoor, SW England, but are limited to terrain underlain by metasedimentary rocks and dolerite, and absent from granite areas. H...
Published in: | Permafrost and Periglacial Processes |
---|---|
Main Authors: | , |
Format: | Article in Journal/Newspaper |
Language: | unknown |
Subjects: | |
Online Access: | https://doi.org/10.1002/ppp.1739 |
id |
ftrepec:oai:RePEc:wly:perpro:v:23:y:2012:i:2:p:152-161 |
---|---|
record_format |
openpolar |
spelling |
ftrepec:oai:RePEc:wly:perpro:v:23:y:2012:i:2:p:152-161 2023-05-15T17:57:24+02:00 Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin James Killingbeck Colin K. Ballantyne https://doi.org/10.1002/ppp.1739 unknown https://doi.org/10.1002/ppp.1739 article ftrepec https://doi.org/10.1002/ppp.1739 2020-12-04T13:31:25Z Extensive fields of vegetated, dome‐shaped earth hummocks 5–35 cm high and typically 80–200 cm in diameter occur on slopes of up to 15° at elevations of 320–440 m asl on Dartmoor, SW England, but are limited to terrain underlain by metasedimentary rocks and dolerite, and absent from granite areas. Hummocks occur within archaeological sites, implying formation within the last ~ 3000 years and ruling out development over permafrost. The hummocks are composed of frost‐susceptible silty soil (modal grain size 10–100 µm) with occasional clasts, but exhibit no evidence for cryoturbation or diapirism. Hummock size and spacing are fairly consistent at particular sites but vary between sites. Hummock age, distribution and characteristics are incompatible with non‐frost action origins and most proposed frost action origins (cryostatic pressure, soil circulation, permafrost aggradation, soil injection), but regular spacing and granulometry favour initiation by differential frost heave under conditions of periodic shallow (0.2–0.4 m) seasonal ground freezing. We suggest that hummock growth may reflect migration of silt in advance of inclined freezing planes until equilibrium is achieved with soil loss down hummock sides. Our results confirm that hummock formation by frost action occurs on silty soils in humid cool temperate climates with only limited seasonal frost penetration. Copyright © 2012 John Wiley & Sons, Ltd. Article in Journal/Newspaper permafrost RePEc (Research Papers in Economics) Permafrost and Periglacial Processes 23 2 152 161 |
institution |
Open Polar |
collection |
RePEc (Research Papers in Economics) |
op_collection_id |
ftrepec |
language |
unknown |
description |
Extensive fields of vegetated, dome‐shaped earth hummocks 5–35 cm high and typically 80–200 cm in diameter occur on slopes of up to 15° at elevations of 320–440 m asl on Dartmoor, SW England, but are limited to terrain underlain by metasedimentary rocks and dolerite, and absent from granite areas. Hummocks occur within archaeological sites, implying formation within the last ~ 3000 years and ruling out development over permafrost. The hummocks are composed of frost‐susceptible silty soil (modal grain size 10–100 µm) with occasional clasts, but exhibit no evidence for cryoturbation or diapirism. Hummock size and spacing are fairly consistent at particular sites but vary between sites. Hummock age, distribution and characteristics are incompatible with non‐frost action origins and most proposed frost action origins (cryostatic pressure, soil circulation, permafrost aggradation, soil injection), but regular spacing and granulometry favour initiation by differential frost heave under conditions of periodic shallow (0.2–0.4 m) seasonal ground freezing. We suggest that hummock growth may reflect migration of silt in advance of inclined freezing planes until equilibrium is achieved with soil loss down hummock sides. Our results confirm that hummock formation by frost action occurs on silty soils in humid cool temperate climates with only limited seasonal frost penetration. Copyright © 2012 John Wiley & Sons, Ltd. |
format |
Article in Journal/Newspaper |
author |
James Killingbeck Colin K. Ballantyne |
spellingShingle |
James Killingbeck Colin K. Ballantyne Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin |
author_facet |
James Killingbeck Colin K. Ballantyne |
author_sort |
James Killingbeck |
title |
Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin |
title_short |
Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin |
title_full |
Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin |
title_fullStr |
Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin |
title_full_unstemmed |
Earth Hummocks in West Dartmoor, SW England: Characteristics, Age and Origin |
title_sort |
earth hummocks in west dartmoor, sw england: characteristics, age and origin |
url |
https://doi.org/10.1002/ppp.1739 |
genre |
permafrost |
genre_facet |
permafrost |
op_relation |
https://doi.org/10.1002/ppp.1739 |
op_doi |
https://doi.org/10.1002/ppp.1739 |
container_title |
Permafrost and Periglacial Processes |
container_volume |
23 |
container_issue |
2 |
container_start_page |
152 |
op_container_end_page |
161 |
_version_ |
1766165825978368000 |