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| Titel |
Reconstruction of mass balance of Nevado Coropuna glaciers (Southern Peru) for Late Pleistocene, Little Ice Age and the present. |
| VerfasserIn |
J. Úbeda, D. Palacios |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026059
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| Zusammenfassung |
| The Nevado Coropuna volcanic complex (15th 31’S-72 º 39 º W) is the quaternary
stratovolcano northernmost of the central volcanic zone (CVZ) in the western flank of the
Central Andes (Southern Peru). This consists in four adjacent volcanic buildings that are
occupied over 5.100-5.700 masl by a system of glaciers covering an area of 47 Km2 in 2007
(Ubeda et al, 2008). The maximum expansion of glaciers during the Pleistocene affected an
area of ~449 Km2, dropping to altitudes around 3.600-4800 m (Ubeda et al, 2007). In this
work were mapped several hundreds of moraines which constitute a record of climate change
since the last glacial maximum (LGM). Current glacier system is formed by dozen of glaciers
descending slope down in all directions. Coropuna complex is an excellent laboratory for to
investigate the control that climate change, tectonics and volcanism exert on the dynamics of
glaciers, a scale of tens of years (by studying current glaciers) and also of tens of
thousands of years (by analyzing the geomorphological evidence of its evolution in the
past). Ubeda et al. (2008) analyzed the evolution of eighteen glaciers of Nevado
Coropuna using indicators as surfaces and Equilibrium Line Altitudes (ELAs) of ice
masses in 2007, 1986, 1955, Little the Ice Age (LIA) and Last Glacial Maximum
(LGM). The glaciers were grouped into two sets: NE group (seven glaciers) and
SE group (eleven glaciers). The work included statistical series of ELAs in each
phase, estimates by Area x Altitud Balance Ratio (AABR) method, which was
proposed by Osmaston (2005), in addition with estimates of timing (~17Cl36 Ka) and
magnitude (~ 782-911 m) of ELA depression during LGM. The work included
statistical series of ELAs in each phase, estimates by the method Area x Altitud
Balance Ratio (AABR) proposed by Osmaston (2005), and in addition estimates of the
timing (~17Cl36 Ka) and magnitude (~ 782-911 m) of ELA depression during
LGM.
The objective of this work is to estimate the current and past mass balance of glaciers in
these phases (2007, 1986, 1955, LIA and LGM) in order to assess the current state of glaciers
and deduct the regimes of temperature and precipitation for present and for LGM. To achieve
this target were installed in 2007 in the gorge of Queñua Ranra (NE quadrant of Coropuna
complex) four stations, that are respectively at 4886 m (E1), 5564 m (E2), 5694 (E3) m and
5822 m (E4). The stations consist of a sensor in air and one (E3) or two sensors in ground
(E1).
The sensors record temperature at intervals of 30 minutes (sensors 12, 13, 22 and 32) or
45 minutes (11, 21, 31 and 41), with precision of tenths of a degree Celsius (º C). The first
digit of the name of the sensors referred to the station (arranged in increasing altitude) and the
second at his position (eg 11-air, 12-ground and 13-deep ground, in the station E1). The
records of Ta and Ts have allowed to define homogeneous data sets of 365 days
(12-11-2007/11-11-2008). With these data have been calculated for each day and each sensor
the average temperatures, and the minimum and maximum temperature variations and
was used to estimate the vertical thermal gradient (δT/δZ) between the stations.
In E1, Ta = 3.9 º C and Ts =6.8ºC. At E3, Ta=-2.9ºC and Ts=1.3ºC. The rain has
been extrapolated from the average of the 1965-2003 series (39 years) from the
station of Andahua (15 Ë 29’36 "S-72 Ë 20’56" W, 3587 m), 20 km to NE of the
eastern summit of Coropuna, resulting in the level E1 (4886 m) a value of P = 494
mm.
The availability of the temperature series has allowed develop the model of mass balance
using an adaptation of the method Klein et al. (1999) developed from an earlier proposal
(Kaser 1995). The method is to solve two equations. Equation 1: a=Ïm/Lm[(Qr+α(Ta-Ts)],
where a is the value of the ablation (mm), Ïm duration of ablation (days), Lm the latent heat
of fusion (3.34x105J/kg), Qr heat available for melting in the form of net radiation
(MJ/day/m), α a coefficient of mass transferred by heat sensitive (0864 MJ/day), and Ta and
Ts air and soil temperature, respectively. Equation 2: b=c–a, where b is the mass balance
(mm) and a the ablation (mm). Using the equation 1, maintaining constant Lm, and α, the
values of Ta, Ts, Ïm, a, c and Qr in each altitude has been estimated as follows: The
values of Ta, Ts have been deducted respectively of the data from the sensors 11-31
and 12-32, using the linear temperature gradients (δT/δZ) previously deducted. c
values have been deducted from the data of Andahua using the linear gradient of
accumulation used by Klein et al (1999): δc/δZ=0,1 mm/m. The values of Ïm and
Qr have been deducted from the value of Ta, whereas at the level Za where Ta=0,
Ïm=0 and Qr =0, and applying from that altitude gradients linear δÏm/δZ=0,4day/m
y δQr/δZ=0,1ºC/m (Klein et al, 1999), positive if ÎZ>0 and negative if ÎZ0) ELA
AABBR and climate are in disequilibrium and the loss of volume, the effect of
ablation, is evident across the surface of the glaciers below the level Zb=0. In gorge
Santiago (ÎZ |
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