Editing Permafrost (section)

=== Massive ground ice ===
[[File:Coulombe 2019 ground ice diagram.png|thumb|Labelled example of a massive buried ice deposit in [[Bylot Island]], Canada<ref name="Coulombe2019" />]]

When the ice content of a permafrost exceeds 250 percent (ice to dry soil by mass) it is classified as massive ice. Massive ice bodies can range in composition, in every conceivable gradation from icy [[mud]] to pure ice. Massive icy beds have a minimum thickness of at least 2&nbsp;m and a short [[diameter]] of at least 10&nbsp;m.<ref name="Mackay1973">{{Cite conference |last=Mackay |first=J. Ross |title=Problems in the origins of massive icy beds, Western Arctic, Canada |conference=Permafrost: North American Contribution – Second International Conference |volume=2 |pages=223–228 |year=1973 |isbn=978-0-309-02115-9 |url=https://books.google.com/books?id=SjErAAAAYAAJ&pg=PA191 }}</ref> First recorded North American observations of this phenomenon were by European scientists at [[Canning River (Alaska)]] in 1919.<ref name="French2007">{{cite book |last=French |first=H. M. |title=The Periglacial Environment |publisher=Wiley |edition=3 |date=26 January 2007 |location=Chichester |chapter=5 |pages=83–115 |isbn=978-1-118-68493-1 |doi=10.1002/9781118684931.ch5 }}</ref> Russian literature provides an earlier date of 1735 and 1739 during the Great North Expedition by P. Lassinius and [[Khariton Laptev]], respectively. Russian investigators including I. A. Lopatin, B. Khegbomov, S. Taber and G. Beskow had also formulated the original theories for ice inclusion in freezing soils.<ref name="Shumskiy-Vtyurin1963">{{Cite conference |last1=Shumskiy |first1=P. A. |last2=Vtyurin |first2=B. I. |title=Underground ice |conference=Permafrost International Conference |issue=1287 |pages=108–113 |year=1963 |url=https://books.google.com/books?id=3jErAAAAYAAJ&q=utilidors+in+permafrost&pg=PA441 }}</ref>

While there are four categories of ice in permafrost – pore ice, ice wedges (also known as vein ice), buried surface ice and intrasedimental (sometimes also called constitutional<ref name="Shumskiy-Vtyurin1963" />) ice – only the last two tend to be large enough to qualify as massive ground ice.<ref name="Mackay1992">{{Cite journal |last1=Mackay |first1=J. R. |last2=Dallimore |first2=S. R. |title=Massive ice of Tuktoyaktuk area, Western Arctic coast, Canada |journal=Canadian Journal of Earth Sciences |volume=29 |issue=6 |pages=1234–1242 |doi=10.1139/e92-099 |year=1992 |bibcode=1992CaJES..29.1235M }}</ref><ref name="Lacelle2022">{{Cite journal |last1=Lacelle |first1=Denis |last2=Fisher |first2=David A. |last3=Verret |first3=Marjolaine |last4=Pollard |first4=Wayne |date=17 February 2022 |title=Improved prediction of the vertical distribution of ground ice in Arctic-Antarctic permafrost sediments |journal=Communications Earth & Environment |volume=3 |issue=31 |page=31 |doi=10.1038/s43247-022-00367-z |bibcode=2022ComEE...3...31L |s2cid=246872753 }}</ref> These two types usually occur separately, but may be found together, like on the coast of [[Tuktoyaktuk]] in western [[Arctic Canada]], where the remains of [[Laurentide Ice Sheet]] are located.<ref>{{cite journal |last1=Murton |first1=J. B. |last2=Whiteman |first2=C. A. |last3=Waller |first3=R. I. |last4=Pollard |first4=W. H. |last5=Clark |first5=I. D. |last6=Dallimore |first6=S. R. |date=12 August 2004 |title=Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada  |journal=Quaternary Science Reviews |volume=24 |issue=5–6 |pages=681–708 |doi=10.1016/S0277-3791(01)00149-4 }}</ref>

Buried surface ice may derive from snow, frozen lake or [[sea ice]], [[aufeis]] (stranded river ice) and even buried glacial ice from the former [[Pleistocene]] ice sheets. The latter hold enormous value for paleoglaciological research, yet even as of 2022, the total extent and volume of such buried ancient ice is unknown.<ref name="Coulombe2022">{{cite journal |last1=Coulombe |first1=Stephanie |last2=Fortier |first2=Daniel |last3=Bouchard |first3=Frédéric |last4=Paquette |first4=Michel |last5=Charbonneau |first5=Simon |last6=Lacelle |first6=Denis |last7=Laurion |first7=Isabelle |last8=Pienitz |first8=Reinhard |title=Contrasted geomorphological and limnological properties of thermokarst lakes formed in buried glacier ice and ice-wedge polygon terrain |journal=The Cryosphere |date=19 July 2022 |volume=16 |issue=7 |pages=2837–2857 |doi=10.5194/tc-16-2837-2022 |bibcode=2022TCry...16.2837C |doi-access=free }}</ref> Notable sites with known ancient ice deposits include [[Yenisei River]] valley in [[Siberia]], Russia as well as [[Banks Island|Banks]] and [[Bylot Island]] in Canada's [[Nunavut]] and [[Northwest Territories]].<ref>{{Cite journal |last1=Astakhov |first1=Valery I. |last2=Isayeva |first2=Lia L. |title=The 'Ice Hill': An example of 'retarded deglaciation' in siberia |journal=Quaternary Science Reviews |year=1988 |volume=7 |issue=1 |pages=29–40 |doi=10.1016/0277-3791(88)90091-1 |bibcode=1988QSRv....7...29A }}</ref><ref>{{Cite journal |last1=French |first1=H. M. |last2=Harry |first2=D. G. |title=Observations on buried glacier ice and massive segregated ice, western arctic coast, Canada |journal=Permafrost and Periglacial Processes |year=1990 |volume=1 |issue=1 |pages=31–43 |doi=10.1002/ppp.3430010105 |bibcode=1990PPPr....1...31F }}</ref><ref name="Coulombe2019">{{cite journal |last1=Coulombe |first1=Stephanie |last2=Fortier |first2=Daniel |last3=Lacelle |first3=Denis |last4=Kanevskiy |first4=Mikhail |last5=Shur  |first5=Yuri |title=Origin, burial and preservation of late Pleistocene-age glacier ice in Arctic permafrost (Bylot Island, NU, Canada) |journal=The Cryosphere |date=11 January 2019 |volume=13 |issue=1 |pages=97–111 |doi=10.5194/tc-13-97-2019 |bibcode=2019TCry...13...97C |doi-access=free }}</ref> Some of the buried ice sheet remnants are known to host [[Thermokarst#Thermokarst lakes|thermokarst lake]]s.<ref name="Coulombe2022" />

Intrasedimental or constitutional ice has been widely observed and studied across Canada. It forms when subterranean waters freeze in place, and is subdivided into intrusive, injection and segregational ice. The latter is the dominant type, formed after crystallizational differentiation in wet [[sediment]]s, which occurs when water migrates to the freezing front under the influence of [[van der Waals force]]s.<ref name="French2007" /><ref name="Mackay1973" /><ref name="Mackay1992" /> This is a slow process, which primarily occurs in [[silt]]s with [[salinity]] less than 20% of [[seawater]]: silt sediments with higher salinity and [[clay]] sediments instead have water movement prior to ice formation dominated by [[rheological]] processes. Consequently, it takes between 1 and 1000 years to form intrasedimental ice in the top 2.5 meters of clay sediments, yet it takes between 10 and 10,000 years for [[peat]] sediments and between 1,000 and 1,000,000 years for silt sediments.<ref name="Lacelle2022" />

[[File:Massive ice - retrogressive thaw slump - Herschel Island.png|thumb|center|900px|Cliff wall of a retrogressive thaw slump located on the southern coast of [[Herschel Island]] within an approximately {{convert|22|m|ft|adj=on}} by {{convert|1300|m|ft|adj=on}} headwall.]]