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| Titel |
Localized sub-glacial deep karst formation due to water infiltration into glacier crevasses: A case study from Asiago, Italy |
| VerfasserIn |
Nicola Tisato, Marcel Frehner, Leonardo Busellato, Giovanni Grasselli |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104051
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| Publikation (Nr.) |
 EGU/EGU2015-3472.pdf |
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| Zusammenfassung |
| In karstic plateaus, deep karst phenomena (e.g. abysses) are the preferential pathways for
surface water to penetrate the Earth’s crust. After percolation along diaclases and meanders,
the infiltrated water often springs at the foot of the karstic plateau, potentially representing a
valuable water resource. Thus, it is crucial to understand the formation and distribution of
deep karst phenomena, for instance to predict karstic groundwater flow paths or to preserve
water resources from pollution.
The role of glaciers in enhancing the formation of deep karst is not yet clear. On the one
hand, chilly water retains more CO2 which increases its acidity and efficiency in
corroding carbonates. On the other hand, glaciers obliterate the soil and vegetation
covering the developing karst decreasing the quantity of humic acids dissolved in the
surface water. Nevertheless, ice-caps may play a key role in controlling how and
where surface water can access the developing karstic system. Due to the presence
of a glacier, some sub-glacial areas may not be reached by surface water, which
prevents karstification, while other areas may be connected to intra- or sub-glacial flow
paths possibly leading to localized kartification in these areas. Here we investigate
the relationship between sub-glacial topography and the development of preferred
intra-glacier flow paths and how this relationship leads to localized sub-glacial
karstification. As a case study site, we use the karstic plateau of Asiago in Northern
Italy.
The Asiago plateau (https://goo.gl/maps/bLezx) is mainly composed of Permian to
Cretaceous rocks. The northern and southern boundaries of the plateau are marked by two
Alpine trusts, which uplifted the plateau during the Alpine orogeny to ~1500 m above the
Po flood plain delimiting the plateau to the South. The Asiago plateau extends
for ~600 km2 and contains ~2100 natural caves, including many significantly
deep caves such as the deepest cave of Veneto: the 1011 m deep Malga Fossetta
abyss.
During the last glaciation only the northern part of the plateau was covered by glaciers, which
modeled the landscape and deposited moraines. Although the lithology is the same (Calcari
grigi fm.), we show by applying spatial-statistical methods that the northern part is richer in
caves, which we propose to be due to intra- and sub-glacial processes. We use a digital
elevation model (DEM) of the Asiago plateau and employ a finite-element model to simulate
the flow of an ice-cap. Our results demonstrate that the glacier undergoes localized
fracturing when overflowing topographic obstacles. The resulting vertical crevasses
allow surface water to infiltrate the glacier and eventually reach the rock surface.
Thanks to the glacial abrasion, the water can infiltrate rock joints creating shafts and
meanders.
We suggest that sub-glacial deep karstification is enhanced nearby glacier crevasses. Our
theory is supported by observations in the northern part of the Asiago plateau, where many
caves are aligned with topographic highs and exhibit morphologies related to water flow.
Our study sheds light on sub-glacial cave formation helping to forecast locations
beneath currently retreating glaciers, which might conceal highly karstified areas. |
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