Former cold-wet ice polythermal glaciers inferred from erratics and moraine's Schmidt Hammer ages at the Madriu valley, Principality of Andorra (SE- Pyrenees)

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RESEARCH POSTER PRESENTATION DESIGN © 2012
www.PosterPresentations.com
© 20
21
Be
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A Schmidt hammer type-L field campaign (SHED) has been conducted on 24th and
25th September 2021, hammering on glacial boulders from the Madriu valley
located at the upper Valira d’Orient bassin (Stating
N42º30’14.60’’–E1º33’08.85’’–1244 m / N42º28’18.38’’–E1º39’33.77’’–2670 m
ending)
Setting
Discussion and conclusions
Schmidt hammer data from the Madriu valley unravels continuous deglaciation of
the glacier front. The size of the Madriu glacier reduces progressively and
incorporates erratic boulders from former paraglacial activity, during recessions
(red line). Chronostratigraphy form La Massana ice-dammed palaeolake (Turu et
al., 2017) and the Madriu glacier evolution match. Low base levels or
unconformities within La Massana correspond to the erratics on the top-most part
of the Madriu valley (above 2200 a.s.l). Glacier front stabilisations and moraine
build-up coincide with high base levels in La Massana (ice-damming increase)
(Turu, 2023).
Interpretation
Bibliography
GÓMEZ-ORTÍZ, A., 1996 – El relleu d’Andorra: morfologia glacial i periglacial. In: Ministeri d’Educació-Joventut-Esports (Ed.),
Monografia de geografia, 3, (Andorra), 129 pp
TOMKINS M. D., DORTCH J. M., HUGHES P. D., HUCK J. J., STIMSON A. G., DELMAS M., CALVET M., PALLÀS R., 2018 – Rapid
age assessment of glacial landforms in the Pyrenees using Schmidt hammer exposure dating (SHED). Quaternary Research, 90(1), 26-
37. https://doi.org/10.1017/qua.2018.12
TURU V., CALVET M., BORDONAU J., GUNNELL Y., DELMAS M., VILAPLANA J.M., JALUT G., 2017 – Did Pyrenean glaciers
dance to the beat of global climatic events? Evidence from the Würmian sequence stratigraphy of an ice-dammed palaeolake
depocentre in Andorra. In Hughes, P. D. & Woodward, J. C. (eds), Quaternary Glaciation in the Mediterranean Mountains, Geological
Society, London, Special Publications, 433(1), 111-136, http://doi.org/10.1144/SP433.6
TURU V. (2023) Mid-Late Pleistocene glacial dynamics in the Valira valleys (Principality of Andorra). Asymmetries within the Pyrenees
and correlation across the westernmost European mountain ranges. PhD Thesis, University of Barcelona, 500 p
(1) Marcel Chevalier Foundation, Andorra la Vella, Principat d’Andorra, igeofundacio@andorra.ad
(2) Facultat de Geografia de la Universitat de Barcelona, (Spain)
(3) GEO3 SL, Av. Príncep Benlloch 66, AD 500, Andorra la Vella, Principat d’Andorra
Valenti TURU MICHELS (1) Josep VENTURA ROCA (1,2) & Xavier ROS VISÚS (3)
Former cold –wet ice polythermal glaciers inferred from erratics and
moraine’s Schmidt Hammer ages at the Madriu Valley
Principality of Andorra (SE – Pyrenees)
Deglaciation of the Madriu valley and the regression
line that allows to determine a precise frontal
position from a particular age on the bottom of the
valley
Original from Gomez-Ortíz (1996). Overprinted the Schmidt Hamer measure stations, from the main valley (M) and
from the Portelleta glacier cirque (P). Legend: 1) Acute glacial cirque, 2) Bedrock step within the glacial cirque, 3)
Scarp, 4) Overdeepened depression, 5) Glacial valley ridges, 6) Polished bedrock, 7) Hanging valley, 8) Moraine, 9)
Undifferenciated till, 10) Moraines from the last period, 11) Transfluence of ice, 12) Lobulated soils from gelifuction,
13) Peat-bog, 14) nivation corry, 15) Bedrock affected by gelifraction, 16) Hörn, 17) Tor, 18) Rock glaciers, 19)
Avalanche pass, 20) Debris cone, 21) Scree cone, 22) Colluvium, 23) Gorge, 24) Erosion, 25) Alluvial fan cone, 26)
Lake, 27) Bedrock scarp, 28) Joints, 29) Orthogonal jointing, 30) Denudation plain.)
Rebound results from the measured boulders at different stations from the Madriu
SHED results following the Carlit calibration curve
from Tomkins et al. (2018). Site references are by
height in meters above the sea level including the
letter of their position on the valley (M) or in the
cirque (P).
Deglaciation of the Madriu
valley. Regression best fit
from SHED plotted ages.
The age of the main
topographical steps of the
valley are obtained from
such regression
Data agrees that paraglacial on top
and moraine build-up on the lowland
valley were contemporary. To explain
the latter, we invoke a languid ice
flow (cold ice) above the ELA where
the frequent occurrence of erratics
matches. A tempered glacier tongue
below the ELA may exist in the Madriu
valley, advancing to the main Andorra
glacier.A slow or very slow ice flow
(cold ice) above the ELA and the
frequent occurence of erratics match,
except for the yougest erratic
identified which flowed within a
surging glacier ice mass ending at
Fontverd. A tempered glacier tongue
below the ELA may existed in the
Madriu valley. Cold ice type could
have coexisted above the ELA and
allowed the former presence of
polythermal glaciers in Andorra during
the MIS 2. Nevertheless, younger
erratics and moraine construction
identified a surging ice mass during
the Older Dryas.
Resistivity measuSchema showing the erratics evolution
on the glacier above the ELA. Paraglacial boulders benefit
from the zeroing exposure from polished glacial surfaces
(on top of the figure). Once the boulder is incorporated
on the glacier surface is subjected to exposure and
weathering until its deposition.res on glacier
Mountain glacier landsystem provide geomorphological and sedimentological
evidence of former glaciations subject to past climate variability. By
reconstructing the glacial phases, we approach the causes of the mountain
glaciers’ length and type of ice within landforms and known chronology
We present the firsts results of the Schmidt hammer (SHED) type-L field campaign
conducted on 24th and 25th September 2021, hammering on glacial boulders from
the Madriu valley (E Andorra, SE Pyrenees) and measuring their rebound energy
value (R). The characteristics, operating principles and procedures for using the
SH are according to the standard ISRM recommendations methods
Data
Results
Representation of the SHED data from the Madriu valley (red, green and blue dots), During deglaciation the Madriu
glacier reduce its size progressively (blue line) and incorporated erratic boulders from former paraglacial activity during
recessions (red dotted line). Solid green line, glacier front evolution during the Last Termination, including a surging
Madriu that correlates with the Older Dryas. Dotted green line, theoretical evolution of the ELA dividing the dominant
type of ice in the Madriu valley.