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| Titel |
Pleistocene periglacial cryogenic mounds (lithalsas) on basalt plateaus in the western Pannonian Basin |
| VerfasserIn |
Krisztina Sebe, Gábor Csillag |
| 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 |
250113061
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| Publikation (Nr.) |
 EGU/EGU2015-13257.pdf |
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| Zusammenfassung |
| On some basalt plateaus of the western Pannonian Basin, Hungary, fields of circular
depressions occur. They are traditionally called „basalt karst” and their formation has been
attributed either to collapse over karstifying rocks or to anthropogenic action (quarrying);
however, both of these theories are questionable.
The depressions are situated between elevations of 350-500 m a.s.l. and are
characteristically surrounded by circular raised rims or ramparts. They measure a few m-s (up
to ~10 m) in diameter, the ramparts emerge 0.5-1.5 m above the surrounding level ground
and encircle a depression of 1-2 (-3) m deep in the middle. Depressions cluster in well
delineated, high-density groups, with individual fields containing several dozens of these
forms. Neighbouring ramparts are tightly packed, often interfere and depressions can thus
coalesce creating composite forms. The ramparts are composed of coarse (dm-sized)
basalt blocks, whose material is identical to that of the surrounding terrain and
seems to originate from the depression. Many of the depressions host ephemeral
ponds.
Raised rims exclude formation of these landforms by any karstic processes. The
anthropogenic theory is opposed by the lack of the remains of any facilities (e.g. roads), of
tools and by the very illogical distribution and geometry of depressions from the point of
human use. On the contrary, we interpret these ramparted depressions as being of periglacial
origin, remnants of cryogenic mounds. The central depression and the emergent rampart can
be well explained by the ice core raising the overlying rock and by the radial downsliding of
this material on the ice core to the margins. Within cryogenic mounds, clustering and size of
the forms fits the characteristics of perennial frost mound without peat cover, i.e. lithalsas or
minerogenic palsas.
Cryogenic mounds are important paleoclimatic indicators. Based on modern
analogs, these lithalsa scars indicate the former presence of discontinuous or scattered
permafrost, a mean annual temperature of -3 to -6Ë C and a maximum for the mean
temperature of the warmest month around 10Ë C. Frost mound formation could be
promoted by high water content in the weathered surficial zone of the basalt and by the
removal of insulating snow cover by strong wind action, already documented in
the area for the Pleistocene. These are the southernmost lithalsa scars reported in
Europe.
Work has been supported by the OTKA project K 106197. |
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