Jökulhlaup process Jökulhlaup

1 jökulhlaup process

1.1 subglacial water generation
1.2 supraglacial , subglacial water flow
1.3 episodic releases

jökulhlaup process
subglacial water generation

subglacial meltwater generation 1 key understanding of subglacial meltwater flow. meltwater may produced on glacier surface (supraglacially), below glacier (basally) or in both locations. ablation (surface melting) tends result in surface pooling. basal melting results geothermal heat flux out of earth, varies location, friction heating results ice moving on surface below it. analyses piotrowski concluded that, based on basal meltwater production rates, annual production of subglacial water 1 typical northwestern germany catchment 642x10 m during last weichselian glaciation.

supraglacial , subglacial water flow

meltwater may flow either above glacier (supraglacially), below glacier (subglacially/basally) or groundwater in aquifer below glacier result of hydraulic transmissivity of subsoil under glacier. if rate of production exceeds rate of loss through aquifer, water collect in surface or subglacial ponds or lakes.

the signatures of supraglacial , basal water flow differ passage zone. supraglacial flow similar stream flow in surface environments—water flows higher areas lower areas under influence of gravity. basal flow under glacier exhibits significant differences. in basal flow water, either produced melting @ base or drawn downward surface gravity, collects @ base of glacier in ponds , lakes in pocket overlain hundreds of metres of ice. if there no surface drainage path, water surface melting flow downward , collect in crevices in ice, while water basal melting collects under glacier; either source can form subglacial lake. hydraulic head of water collected in basal lake increase water drains through ice until pressure grows high enough either force path through ice or float ice above it.

episodic releases

if meltwater accumulates, discharges episodic under continental ice sheets under alpine glaciers. discharge results when water collects, overlying ice lifted, , water moves outward in pressurized layer or growing under-ice lake. areas ice lifted (i.e. areas thinner overlying ice sheets) lifted first. hence water may move terrain underlying glacier if moves toward areas of lower overlying ice. water collects, additional ice lifted until release path created.

if no preexisting channel present, water released in broad-front jökulhlaup can have flow front tens of kilometres wide, spreading out in thin front. flow continues, tends erode underlying materials , overlying ice, creating tunnel valley channel reduced pressure allows of glacial ice settle underlying surface, sealing off broad front release , channelizing flow. direction of channel defined overlying ice thickness , second gradient of underlying earth, , may observed run uphill pressure of ice forces water areas of lower ice coverage until emerges @ glacial face. hence configuration of various tunnel valleys formed specific glaciation provides general mapping of glacier thickness when tunnel valleys formed, particularly if original surface relief under glacier limited.

the rapid, high-volume discharge highly erosive, evidenced debris found in tunnels , @ mouth of tunnels, tends coarse rocks , boulders. erosive environment consistent creation of tunnels on 400 m deep , 2.5 km wide, have been observed in antarctic.

piotrowski has developed detailed analytic model of process, predicts cycle follows:

^ shaw, john; a. pugin; r. r. young (december 2008). meltwater origin antarctic shelf bedforms special attention megalineations . geomorphology (3–4): 364–375. bibcode:2008geomo.102..364s. doi:10.1016/j.geomorph.2008.04.005. 
^ smellie, john l.; j. s. johnson; w. c. mcintosh; r. esserb; m. t. gudmundsson; m. j. hambrey; b. van wyk de vriese (april 2008). 6 million years of glacial history recorded in volcanic lithofacies of james ross island volcanic group, antarctic peninsula . palaeogeography, palaeoclimatology, palaeoecology. 260 (1–2): 122–148. doi:10.1016/j.palaeo.2007.08.011. 
^ piotrowski, jan a. (1997). subglacial hydrology in north-western germany during last glaciation: groundwater flow, tunnel valleys, , hydrological cycles (pdf). quaternary science reviews. 16 (2): 169–185. bibcode:1997qsrv...16..169p. doi:10.1016/s0277-3791(96)00046-7. 
^ smellie, john l. (may 2008). basaltic subglacial sheet-like sequences: evidence 2 types different implications inferred thickness of associated ice . earth-science reviews. 88 (1–2): 60–88. bibcode:2008esrv...88...60s. doi:10.1016/j.earscirev.2008.01.004. 
^ waterbed analogy can applied here—the water moves under pressure of overlying ice, when mass placed on water bed.
^ wingham2006