Holocene alluvial-fan development in the Macgillycuddy's Reeks, southwest Ireland

E Anderson, S Harrison, D G Passmore, Timothy Michael Mighall

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31 Citations (Scopus)

Abstract

Holocene alluvial landforms in the Macgillycuddy's Reeks, southwest Ireland, mere investigated to determine the controls and timing of postglacial geomorphic activity. Detailed geomorphologic analysis of three alluvial-fan and debris cones within high-level cirque basins demonstrates evidence of episodic phases of late Holocene surface aggradation and incision. Radiocarbon dates from peat horizons above and below inorganic units show that phases of aggradation cluster into two distinct periods, the first after 230-790 calibrated (cal.) yr A.D. and the second from 1510 cal. yr A.D. to the present. An additional phase of fan aggradation at one site is dated after 1040-1280 cal. yr A.D. All three phases coincide with episodes of enhanced late Holocene valley-door alluviation and debris-flow activity from upland Britain. Alluvial fans and debris cones have developed primarily as a result of the resedimentation of late Midlandian (Wisconsin) drift and talus slopes, and mobilization of materials involved flooding, transitional-flow, and debris-flow processes. Pollen analysis of peat horizons interbedded with alluvial-fan and debris-cone sediments indicates that land-use changes mere an important factor in lowering the threshold for local slope erosion. Phases of aggradation also coincide with well-documented episodes of climate change, and, hence, fan development is probably a function of both anthropogenic and climatic forcing. A sequence of events may have involved initial slope destabilization due to overgrazing and removal of vegetation that mas followed by debris mobilization and fan aggradation during intense rainstorms associated with climate change.

Original languageEnglish
Pages (from-to)1834-1849
Number of pages16
JournalGeological Society of America Bulletin
Volume112
Issue number12
Publication statusPublished - Dec 2000

Keywords

  • alluvial fans
  • Holocene
  • southwest Ireland
  • SCOTTISH HIGHLANDS
  • NORTHWEST ENGLAND
  • SCOTLAND
  • EVOLUTION
  • UPLANDS
  • VALLEY
  • FELLS
  • AGE

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