# Blockfield > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Blockfield > Markdown URL: https://mediated.wiki/source/Blockfield.md > Source: https://en.wikipedia.org/wiki/Blockfield > Source revision: 1329755524 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Surface covered by irregular rocks}} {{Use dmy dates|date=March 2017}} thumb|Felsenmeer in Lautertal-Reichenbach (Odenwald) [[File:Kalmit Felsenmeer.jpg|thumb|Felsenmeer on the [Kalmit](/source/Kalmit) in the [Palatine Forest](/source/Palatine_Forest)]] [[File:Kaser Steinstube.jpg|thumb|Boulder stream of the [Kaser Steinstube](/source/Kaser_Steinstube) near [Triftern](/source/Triftern)]] [[File:Eastern White Pine In Boulder Field PA.jpg|thumb|A photo of a single [eastern white pine](/source/eastern_white_pine) in the nearly barren Boulder Field, [Hickory Run State Park](/source/Hickory_Run_State_Park), PA.]] [[File:'Felsenmeer' Rijksmuseum SK-A-2654.jpeg|thumb|''Felsenmeer'', painting by [Egbert Schaap](/source/Egbert_Schaap) (1912). [Rijksmuseum Amsterdam](/source/Rijksmuseum_Amsterdam)]] A '''blockfield'''Whittow, John (1984). ''Dictionary of Physical Geography''. London: Penguin, 1984, pp. 66 and 190. {{ISBN|0-14-051094-X}}. (also spelt '''block field'''Leser, Hartmut, ed. (2005). ''Wörterbuch Allgemeine Geographie'', 13th ed., dtv, Munich, pp. 107 and 221. {{ISBN|978-3-423-03422-7}}. ), '''felsenmeer''', '''boulder field''' or '''stone field''' is a surface covered by boulder- or block-sized rocks usually associated with a history of volcanic activity, [alpine](/source/alpine_climate) and [subpolar climate](/source/subpolar_climate)s and [periglaciation](/source/periglaciation). Blockfields differ from [scree](/source/scree)s and [talus slope](/source/talus_slope) in that blockfields do not apparently originate from [mass wasting](/source/mass_wasting)s. They are believed to be formed by [frost weathering](/source/frost_weathering) below the surface.Thomas, David S.G. and [Andrew Goudie](/source/Andrew_Goudie_(geographer)) (eds.), ''The Dictionary of Physical Geography'', 3rd edn., Oxford: Blackwell, 2000, p. 215. {{ISBN|0-631-20473-3}}. An alternative theory that modern blockfields may have originated from [chemical weathering](/source/chemical_weathering) that occurred in the [Neogene](/source/Neogene) when the climate was relatively warmer. Following this thought the blockfields would then have been reworked by periglacial action.{{cite journal |last1=Goodfellow |first1=B.W. |last2=Stroeven |first2=A.P. |last3=Fabel |first3=D. |last4=Fredin |first4=O. |last5=M.-H. |first5=Derron |last6=Bintnja |first6=R. |last7=Caffee |first7=M.W. |date=2014 |title=Arctic–alpine blockfields in the northern Swedish Scandes: late Quaternary – not Neogene |url=http://www.earth-surf-dynam.net/2/383/2014/ |journal=Earth Surface Dynamics |volume=2 |issue=2 |pages=383–401 |doi=10.5194/esurf-2-383-2014 |bibcode=2014ESuD....2..383G |access-date=11 July 2016|doi-access=free }}{{cite journal |last=Boelhouwers |first=Jan |date=2004 |title=New Perspectives on Autochthonous Blockfield Development |journal=[Polar Geography](/source/Polar_Geography) |volume=28 |issue=2 |pages=133–146 |doi=10.1080/789610122 |s2cid=129295656 }} Most known blockfields are located in the northern hemisphere. Examples can be found in [Abisko National Park](/source/Abisko_National_Park) in Sweden, [Snowdonia National Park](/source/Snowdonia_National_Park) in Wales, the [Great End](/source/Great_End)-[Scafell Pike](/source/Scafell_Pike) ridge in [England](/source/England), and [Hickory Run Boulder Field](/source/Hickory_Run_State_Park) and [River of Rocks](/source/Hawk_Mountain) in the [Appalachian Mountains](/source/Appalachian_Mountains) of the [United States](/source/United_States). All examples except the first one are outside present day subpolar climate areas, and have thus traditionally been seen as relict [landform](/source/landform)s from past times when these areas were under periglaciation. The term "felsenmeer" comes from the German meaning "sea of rock". In a felsenmeer or blockfield, [freeze-thaw](/source/freeze-thaw) weathering has broken up the top layer of the rock, covering the underlying rock formation with jagged, angular boulders. Freeze-thaw or frost weathering occurs when water that is trapped along [microcracks](/source/Microcracks_in_rock) in rock expands and contracts due to fluctuations in temperature above and below the freezing point. Felsenmeers are formed ''in situ'', meaning that they are not transported during or after their creation. ==Characteristics== ===Surface=== Felsenmeers only form on slopes of 25° or lower. A steeper angle results in transport of the blocks due to gravity. This creates a [talus](/source/Scree) slope, rather than a felsenmeer.Dahl, R. (1966) Block fields, weathering pits and tor-like forms in the Narvik Mountains, Nordland, Norway. ''[Geografiska Annaler](/source/Geografiska_Annaler)'' A 48, 55-85. Crude sorting with boulder [imbrication](/source/imbrication_(sedimentology)) can occasionally be seen on the surface of felsenmeers. ===Profile=== The depth of the boulder field depends on the slope angle, rock types, age, and erosional history. However, a reasonable average for felsenmeer depth is approximately 1 m. Ballantyne (1998)Ballantyne, C.K. (1998). Age and significance of mountain-top detritus. ''[Permafrost and Periglacial Processes](/source/Permafrost_and_Periglacial_Processes)'' 9, 327-345 defines three types of felsenmeer profiles: Type 1 consists of boulders overlying a matrix of fines at some depth below the surface. Type 2 consists of boulders supported by a cohesionless sandy matrix that continues from the surface down through the profile. Type 3 also consists of boulders supported by a matrix, but differs from Type 2 in that the matrix consists of silt and/or clay rather than sand. == Occurrence == Due to the slope requirements they are most commonly found on [plateaus](/source/plateaus).Huggett, John Richard. ''Fundamentals of Geomorphology'', 3rd edn., Routledge, 2011, p. 147. [Basalt](/source/Basalt) and [sedimentary rock](/source/sedimentary_rock)s often produce larger, more numerous felsenmeers than other types of rock.''The New Encyclopædia Britannica'', Volume 8; Volume 14, 1998. Blockfields are most often found in high mountain [periglacial](/source/periglacial) regions near the Arctic Circle, especially in [Iceland](/source/Iceland), the [Canadian](/source/Canada) arctic and [Norway](/source/Norway) and are still active in parts of Central Europe that were not covered by ice sheets. In the [Southern Hemisphere](/source/Southern_Hemisphere) [inactive](/source/relict_(geology)) blockfields can be found in the [Lesotho Highlands](/source/Lesotho_Highlands),{{cite journal|author-last=Sumner |author-first=P.D. |date=2004 |title=Geomorphic and climatic implications of relict openwork block accumulations near Thabana-Ntlenyana, Lesotho |journal=[Geografiska Annaler: Series A, Physical Geography](/source/Geografiska_Annaler%3A_Series_A%2C_Physical_Geography) |volume=86|issue=3 |pages= 289–302|doi=10.1111/j.0435-3676.2004.00232.x |s2cid=128774864 }} and the [Prince Edward Islands](/source/Prince_Edward_Islands).{{cite journal |last1=Boelhouwers |first1=Jan |last2=Holness |first2=Steve |last3=Sumner |first3=Paul |date=2003 |title=The maritime Subantarctic: a distinct periglacial environment |journal=[Geomorphology](/source/Geomorphology_(journal)) |publisher=Elsevier |volume=52 |issue=1 |pages=39–55 |doi=10.1016/S0169-555X(02)00247-7 |bibcode=2003Geomo..52...39B }} == Age == Felsenmeers are, typically, relatively young geomorphological features. Most felsenmeers formed during or since the last [ice age](/source/ice_age) (approximately 20,000 years ago). Others may be pre-glacial features that survived glaciation beneath cold-based glaciers.Matthews, John A. (ed.), ''Encyclopedia of Environmental Change'', 3-volume set, Swansea: Sage, 2014. Their specific age can be determined using [surface exposure dating](/source/surface_exposure_dating), a technique that works best on materials which have been exposed to cosmic rays with little interference from trees or soils. ==See also== *[Stone run](/source/Stone_run) *[Weathering](/source/Weathering) *[Floater](/source/Floater_(geology)) ==References== {{Reflist}} {{Periglacial environment}} {{Authority control}} Category:Rock formations Category:Geomorphology Category:Geotopes --- Adapted from the Wikipedia article [Blockfield](https://en.wikipedia.org/wiki/Blockfield) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Blockfield?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.