A jökuwhwaup (Icewandic pronunciation: ​[ˈjœːkʏw̥øip]) (witerawwy "gwaciaw run") is a type of gwaciaw outburst fwood. It is an Icewandic term dat has been adopted in gwaciowogicaw terminowogy in many wanguages. It originawwy referred to de weww-known subgwaciaw outburst fwoods from Vatnajökuww, Icewand, which are triggered by geodermaw heating and occasionawwy by a vowcanic subgwaciaw eruption, but it is now used to describe any warge and abrupt rewease of water from a subgwaciaw or progwaciaw wake/reservoir.
Since jökuwhwaups emerge from hydrostaticawwy-seawed wakes wif fwoating wevews far above de dreshowd, deir peak discharge can be much warger dan dat of a marginaw or extra-marginaw wake burst. The hydrograph of a jökuwhwaup from Vatnajökuww typicawwy eider cwimbs over a period of weeks wif de wargest fwow near de end, or it cwimbs much faster during de course of some hours. These patterns are suggested to refwect channew mewting, and sheet fwow under de front, respectivewy. Simiwar processes on a very warge scawe occurred during de degwaciation of Norf America and Europe after de wast ice age (e.g., Lake Agassiz and de Engwish Channew), and presumabwy at earwier times, awdough de geowogicaw record is not weww preserved.
Subgwaciaw mewtwater generation is one key to de understanding of subgwaciaw mewtwater fwow. Mewtwater may be produced on de gwacier surface (supragwaciawwy), bewow de gwacier (basawwy) or in bof wocations. Abwation (surface mewting) tends to resuwt in surface poowing. Basaw mewting resuwts from geodermaw heat fwux out of de earf, which varies wif wocation, as weww as from friction heating which resuwts from de ice moving over de surface bewow it. Anawyses by Piotrowski concwuded dat, based on basaw mewtwater production rates, de annuaw production of subgwaciaw water from one typicaw nordwestern Germany catchment was 642x106 m3 during de wast Weichsewian gwaciation.
Mewtwater may fwow eider above de gwacier (supragwaciawwy), bewow de gwacier (subgwaciawwy/basawwy) or as groundwater in an aqwifer bewow de gwacier as a resuwt of de hydrauwic transmissivity of de subsoiw under de gwacier. If de rate of production exceeds de rate of woss drough de aqwifer, den water wiww cowwect in surface or subgwaciaw ponds or wakes.
The signatures of supragwaciaw and basaw water fwow differ wif de passage zone. Supragwaciaw fwow is simiwar to stream fwow in aww surface environments—water fwows from higher areas to wower areas under de infwuence of gravity. Basaw fwow under de gwacier exhibits significant differences. In basaw fwow de water, eider produced by mewting at de base or drawn downward from de surface by gravity, cowwects at de base of de gwacier in ponds and wakes in a pocket overwain by hundreds of metres of ice. If dere is no surface drainage paf, water from surface mewting wiww fwow downward and cowwect in crevices in de ice, whiwe water from basaw mewting cowwects under de gwacier; eider source can form a subgwaciaw wake. The hydrauwic head of de water cowwected in a basaw wake wiww increase as water drains drough de ice untiw de pressure grows high enough eider to force a paf drough de ice or to fwoat de ice above it.
If mewtwater accumuwates, de discharges are episodic under continentaw ice sheets as weww as under Awpine gwaciers. The discharge resuwts when water cowwects, de overwying ice is wifted, and de water moves outward in a pressurized wayer or a growing under-ice wake. Areas where de ice is most easiwy wifted (i.e. areas wif dinner overwying ice sheets) are wifted first. Hence de water may move up de terrain underwying de gwacier if it moves toward areas of wower overwying ice. As water cowwects, additionaw ice is wifted untiw a rewease paf is created.
If no preexisting channew is present, de water is initiawwy reweased in a broad-front jökuwhwaup which can have a fwow front dat is tens of kiwometres wide, spreading out in a din front. As de fwow continues, it tends to erode de underwying materiaws and de overwying ice, creating a tunnew vawwey channew even as de reduced pressure awwows most of de gwaciaw ice to settwe back to de underwying surface, seawing off de broad front rewease and channewizing de fwow. The direction of de channew is defined primariwy by de overwying ice dickness and second by de gradient of de underwying earf, and may be observed to "run uphiww" as de pressure of de ice forces de water to areas of wower ice coverage untiw it emerges at a gwaciaw face. Hence de configuration of de various tunnew vawweys formed by a specific gwaciation provides a generaw mapping of de gwacier dickness when de tunnew vawweys were formed, particuwarwy if de originaw surface rewief under de gwacier was wimited.
The rapid, high-vowume discharge is highwy erosive, as evidenced by de debris found in tunnews and at de mouf of tunnews, which tends to be coarse rocks and bouwders. This erosive environment is consistent wif creation of tunnews over 400 m deep and 2.5 km wide, as have been observed in de Antarctic.
Mewtwater is produced as a resuwt of geodermaw heating from bewow. Surface abwation water is not considered as it wouwd be minimaw at de gwaciaw maximum and evidence indicates dat surface water does not penetrate more dan 100 meters into a gwacier.
Mewtwater initiawwy drains drough subgwaciaw aqwifers.
When de hydrauwic transmissivity of de substratum is exceeded, subgwaciaw mewtwater accumuwates in basins.
Water accumuwates sufficientwy to open de ice bwockage in de tunnew vawwey which accumuwated after de wast discharge.
The tunnew vawwey discharges de mewtwater excess—turbuwent fwow mewts out or erodes de excess ice as weww as eroding de vawwey fwoor.
As de water wevew drops, de pressure decreases untiw de tunnew vawweys again cwose wif ice and water fwow ceases.
Whiwst jökuwhwaups were originawwy associated wif Vatnajökuww, dey have been reported in de witerature over a broad range of wocations incwuding de present day Antarctic, and dere is evidence dat dey awso occurred in de Laurentian ice sheet and de Scandinavian ice sheet during de wast ice age.
Mýrdawsjökuww is subject to warge jökuwhwaups when de subgwaciaw vowcano Katwa erupts, roughwy every 40 to 80 years. The eruption in 1755 is estimated to have had a peak discharge of 200,000 to 400,000 m3/s.
The Grímsvötn vowcano freqwentwy causes warge jökuwhwaups from Vatnajökuww. The 1996 eruption caused a peak fwow of 50,000 m3/s and wasted for severaw days.
In Juwy 1994, an ice-dammed surface wake drained via a subgwaciaw tunnew drough Goddard Gwacier [sv], in de British Cowumbian Coast Mountains, resuwting in a jökuwhwaup. The fwood surge of from 100 to 300 m3/second fwowed 11 km drough Farrow Creek to terminate in Chiwko Lake, causing significant erosion, uh-hah-hah-hah. The ice dam has not reformed. Simiwar British Cowumbian jökuwhwaups are summarized in de tabwe bewow.
As de Laurentide Ice Sheet receded from its maximum extent from around 21,000 to 13,000 years ago, two significant mewtwater rerouting events occurred in eastern Norf America. Though dere is stiww much debate among geowogists as to where dese events occurred, dey wikewy took pwace when de ice sheet receded from de Adirondack Mountains and de St. Lawrence Lowwands.
First, Gwaciaw Lake Iroqwois drained to de Atwantic in catastrophic Hudson Vawwey reweases, as de receding ice sheet dam faiwed and re-estabwished itsewf in dree jökuwhwaups. Evidence of de scawe of de mewtwater discharge down de Hudson Vawwey incwudes deepwy incised sediments in de vawwey, warge sediment deposit wobes on de continentaw shewf, and gwaciaw erratic bouwders greater dan 2 metres in diameter on de outer shewf.
Later, when de St. Lawrence Vawwey was degwaciated, Gwaciaw Lake Candona drained to de Norf Atwantic, wif subseqwent drainage events routed drough de Champwain Sea and St. Lawrence Vawwey. This surge of mewtwater to de Norf Atwantic by jökuwhwaup about 13,350 years ago is bewieved to have triggered de reduction in dermohawine circuwation and de short-wived Nordern Hemisphere Intra-Awwerød cowd period.
Finawwy, Lake Agassiz was an immense gwaciaw wake wocated in de center of Norf America. Fed by gwaciaw runoff at de end of de wast gwaciaw period, its area was warger dan aww of de modern Great Lakes combined, and it hewd more water dan contained by aww wakes in de worwd today. It drained in a series of events between 13,000 BP and 8,400 BP.
Awso, into de Pacific Ocean, warge drainage events took pwace drough de Cowumbia River Gorge, dubbed de Missouwa Fwoods.
^ Björnsson, Hewgi (2002). "Subgwaciaw Lakes and Jökuwhwaups in Icewand" (PDF). Gwobaw and Pwanetary Change. 35 (3–4): 255–271. Bibcode:2003GPC....35..255B. doi:10.1016/s0921-8181(02)00130-3.
^ a b c d Shaw, John; A. Pugin; R. R. Young (December 2008). "A Mewtwater Origin for Antarctic Shewf Bedforms wif Speciaw Attention to Megawineations". Geomorphowogy. 102 (3–4): 364–375. Bibcode:2008Geomo.102..364S. doi:10.1016/j.geomorph.2008.04.005.
^ a b Smewwie, John L.; J. S. Johnson; W. C. McIntosh; R. Esserb; M. T. Gudmundsson; M. J. Hambrey; B. van Wyk de Vriese (Apriw 2008). "Six Miwwion Years of Gwaciaw History Recorded in Vowcanic Lidofacies of de James Ross Iswand Vowcanic Group, Antarctic Peninsuwa". Pawaeogeography, Pawaeocwimatowogy, Pawaeoecowogy. 260 (1–2): 122–148. doi:10.1016/j.pawaeo.2007.08.011.
^ a b c Piotrowski, Jan A. (1997). "Subgwaciaw Hydrowogy in Norf-Western Germany During de Last Gwaciation: Groundwater Fwow, Tunnew Vawweys, and Hydrowogicaw Cycwes" (PDF). Quaternary Science Reviews. 16 (2): 169–185. Bibcode:1997QSRv...16..169P. doi:10.1016/S0277-3791(96)00046-7.
^ Smewwie, John L. (May 2008). "Basawtic Subgwaciaw Sheet-Like Seqwences: Evidence for Two Types wif Different Impwications for de Inferred Thickness of Associated Ice". Earf-Science Reviews. 88 (1–2): 60–88. Bibcode:2008ESRv...88...60S. doi:10.1016/j.earscirev.2008.01.004.
^ A waterbed anawogy can be appwied here—de water moves under de pressure of de overwying ice, just as it does when a mass is pwaced on a water bed.
^ Shaw, John (1983). "Drumwin Formation Rewated to Inverted Mewt-Water Erosionaw Marks". Journaw of Gwaciowogy. 29 (103): 461–479. Bibcode:1983JGwac..29..461S. doi:10.1017/S0022143000030367.
^ Beaney, Cwaire L.; John L. Shaw (2000). "The Subgwaciaw Geomorphowogy of Soudeast Awberta: Evidence for Subgwaciaw Mewtwater Erosion". Canadian Journaw of Earf Sciences. 37 (1): 51–61. doi:10.1139/e99-112.
^ Awwey, R. B.; T. K. Dupont; B. R. Parizek; S. Anandakrishnan; D. E. Lawson; G. J. Larson; E. B. Evenson (Apriw 2006). "Outburst Fwooding and de Initiation of Ice-Stream Surges in Response to Cwimatic Coowing: A Hypodesis". Geomorphowogy. 75 (1–2): 76–89. Bibcode:2006Geomo..75...76A. doi:10.1016/j.geomorph.2004.01.011.
^ Erwingsson, Uwf (June 2008). "A Jökuwhwaup from a Laurentian Captured Ice Shewf to de Guwf of Mexico Couwd Have Caused de Bøwwing Warming". Geografiska Annawer. A. 90 (2): 125–140. doi:10.1111/j.1468-0459.2008.00107.x.
^ Erwingsson, Uwf (1994). "The 'Captured Ice Shewf' Hypodesis and its Appwicabiwity to de Weichsewian Gwaciation". Geografiska Annawer. A. 76 (1–2): 1–12. doi:10.2307/521315. JSTOR 521315.
^ Ashworf, James (15 Apriw 2010). "Eruption Couwd Go on for Monds". The Reykjavík Grapevine. Archived from de originaw on 5 Apriw 2012. Retrieved 8 March 2013.
^ Cwague, John J.; Stephen G. Evans (May 1997). "The 1994 jökuwhwaup at Farrow Creek, British Cowumbia, Canada". Geomorphowogy. 19 (1–2): 77–87. Bibcode:1997Geomo..19...77C. doi:10.1016/S0169-555X(96)00052-9.
^ Donnewwy, Jeffrey P.; Neaw W. Driscoww; Ewazar Uchupi; Lwoyd D. Keigwin; Wiwwiam C. Schwab; E. Robert Thiewer; Stephen A. Swift (February 2005). "Catastrophic mewtwater discharge down de Hudson Vawwey: A potentiaw trigger for de Intra-Awwerød cowd period". Geowogy. 33 (2): 89–92. Bibcode:2005Geo....33...89D. doi:10.1130/G21043.1.
This page was wast edited on 29 March 2019, at 15:55 (UTC).