Geoscience Reference
In-Depth Information
different.mountain.areas..Third,.we.investigated.relationships.between.climate.and.
mass.balance.of.glaciers.by.intensively.monitoring.selected.glaciers.
A.1:100,000-scale.map.of.all.extant.glaciers.of.the.American.West.was.digitally.
compiled.from.existing.maps.and.aerial.photography.(Fountain.et.al..2007),.includ-
ing. 1,523. glaciers. ranging. from. 3,070. m
2
. to. 13.6. km
2
.. At. this. scale. some. smaller.
glaciers. were. not. mapped,. so. a. 1:24,000. glacier. inventory. was. created. to. provide.
a. comprehensive. snapshot. of. glacier. cover. in. the. American. West.. Fountain. et. al..
(2007). report. nearly. 8,300. “glaciers,”. which. in. this. inventory. includes. perennial.
snow.patches.and.small.ice.features..The.1:24,000-scale.map.added.6,770.glaciers.
to. the. inventory. ranging. from. 347. m
2
. to. 10.59. km
2
.. The. glacier. inventory. (http://
www.glaciers.us).contains.interactive.maps,.photographs,.and.other.information,.and.
documents.signiicant.reductions.in.ice.and.snow.since.1900:.66%.in.Montana,.42%.
in.Wyoming,.40%.in.Colorado,.56%.in.California,.30%.in.Oregon,.and.24-46%.in.
various.Washington.locations..Mapped.glaciers.that.are.less.than.0.01.km
2
.(40%.of.
the.total).are.especially.vulnerable.to.warming.trends.
In. Glacier. NP,. Grinnell. Glacier. was. irst. explored. by. George. Bird. Grinnell. in.
1887. and. described. “as. 1,000. feet. high. and. several. miles. across”. (Diettert. 1992)..
About.90%.of.the.ice.that.Grinnell.saw.is.now.gone..Repeat.photographs.(Figure 8.1).
show. that. Grinnell. Glacier. has. retreated. substantially,. become. thinner,. separated.
from.what.is.now.Salamander.Glacier,.formed.a.lake.from.its.own.meltwater,.and.
discharged.icebergs.into.the.lake..A.time-series.map,.observations,.terminus.mea-
surements,. and. photographs. document. a. reduction. from. 2.3. km
2
. to. 0.6. km
2
. from.
1850.to.2006,.with.a.recent.acceleration.in.glacier.recession.(Key.et.al..2002;.Fagre.
and.McKeon.2010).
To. achieve. a. more. accurate. understanding. of. glacier.responses. to. climate,. four.
years. of. seasonal. and. annual. mass. balances. for. Sperry. Glacier. (Glacier. NP). were.
calculated.using.direct.glaciological.methods.augmented.with.data.from.an.adjacent.
weather.station.and.snow.pillow..Net.annual.balance.averaged.-1.0-m.water.equiva-
lent.for.2005-2007..Despite.signiicant.spatial.variability,.Sperry.Glacier.is.primar-
ily.driven.by.climatic.variation.rather.than.topographic.shading,.snow.redistribution.
by.wind,.or.avalanche.inputs..Mass.balance.loss.from.2005.to.2008.is.three.to.four.
times. higher. than. during. the. 1950s,. indicating. that. ice. loss. at. Sperry. Glacier. has.
accelerated.in.recent.decades.due.to.warmer.temperatures.
Snow.is.critical.to.maintaining.glacier.mass.and.drives.other.mountain.ecosystem.
dynamics. ranging. from. avalanche. frequency. to. timing. of. alpine. plant. emergence..
Snowpacks.across.Western.mountains.now.contain.less.moisture.(Mote.et.al..2005;.
Mote. 2006;. Barnett. et. al.. 2008),. melt. earlier. (Regonda. et. al.. 2005;. Stewart. et. al..
2005;. McCabe. and. Clark. 2005),. and. contribute. less. to. streamlow. (Hamlet. et. al..
2007).than.they.did.prior.to.1950,.with.spring.and.summer.temperatures.as.the.pri-
mary.driver.of.earlier.snowmelt.runoff..WMI.has.examined.the.following.for.each.
of. the. ive. WMI. bioregions:. (1). changes. in. evolution. of. snowpack. throughout. the.
accumulation.and.melt.season;.(2).regional.rates.of.temperature.change,.especially.
changes.in.the.0°C.freeze.threshold.at.low-.and.mid-elevations;.(3).changes.in.the.
amount.and.timing.of.regional.streamlows;.and.(4).relationships.between.changes.
in.the.evolution.of.regional.snowpack.and.streamlow.
