The Pezza Plain, a closed tectonic basin with a catchment area of about 25 km2, is located on the Velino Massif, at the altitude of 1,450-1,530 m. The mountain crests that encircle the Plain, reach altitudes up to 2,271 m a.s.l. and commonly consist of Meso-Cenozoic carbonatic rocks. There is not an actual superficial drainage on the Plain nor are karst sinkholes present on its surface. The stratigraphic study of the Late Pleistocene and Holocene sediments allowed for the identification of five lacustrine formations. The lake, which is presently extinct, reached a maximum area of about 1 km2 and a depth of 8-10 m during highstands. The Pezza Plain lake would have had five periods of maximum level, Le.: i) in an unspecified time preceding the Last Glacial Maximum; ii) during the Last Glacial Maximum, when it reached the sill level and outflowed toward Altopiano delle Rocche; iii) during a period from about 5,790±70 to 3,240±65 years B.P.; iv) during a period much more recent than 3,175±65 B.P. and older than 1,575±65 years B.P.; v) in a period after 1,575±65 years B.P. and before 926±40 years B.P. The lake level was low up to dry in the intervals between these periods. It is probable that the lake disappeared for a certain time, at least from 3,240±65 to 3,175±65 years B.P. when the only eolian sediments recognized in the sedimentary series were deposited. At about 3,400±50 years B.P., in the western portion of the Pezza Plain, another ephemeral short-living lake of small area formed due to the damming action of detrital and colluvial deposits. Lake level fluctuations were linked to climatic changes which modified the hydrologic equilibrium in the catchment area. Nevertheless, the periods of absence of the lake-like the present one-or of low lake levels, do not always correspond with arid climatic conditions. At present, even if there is no lake on the Plain, the mean annual rainfall is ca. 1,200-1,300 mm. With regard to the past, the development of soils-andò soils, in particular-indicates that even when the lake was low or dry, climate was not arid. Probably temperature was one of the main factors controlling the variations in the hydraulic equilibrium: elevated temperatures favour evaporation and therefore, for equal rainfall amounts , there is a decrease in lake level up to the lake drying up. Morphological stability and development of the present soil (following a phase of aridity marked by absence of the lake and deposition of detrital and colluvial deposits, which occurred during part of the Medieval period) are factors that seem to make the Pezza Plain present situation more similar to that of the time immediately before 6,090±80 to 5,790±70 years B.P. The drastic areal reduction and disappearance of the Pezza Plain ephemeral lake in the last 1,000 years, is not an isolated case: also some ephemeral lakes found on the Meta Massif at similar altitudes, have recently disappeared. Also these lakes indicate variations in the catchment areas hydraulic equilibrium such as it has been noticed for the Pezza Plain lake.
Late Pleistocene and Holocene level fluctuations of the ephemeral lake of the Pezza Plain (Abruzzo, Central Italy) [Le oscillazioni tardo-pleistoceniche ed oloceniche del lago effimero del piano di pezza (Abruzzo- Italia centrale)]
Giraudi, C.
1997-01-01
Abstract
The Pezza Plain, a closed tectonic basin with a catchment area of about 25 km2, is located on the Velino Massif, at the altitude of 1,450-1,530 m. The mountain crests that encircle the Plain, reach altitudes up to 2,271 m a.s.l. and commonly consist of Meso-Cenozoic carbonatic rocks. There is not an actual superficial drainage on the Plain nor are karst sinkholes present on its surface. The stratigraphic study of the Late Pleistocene and Holocene sediments allowed for the identification of five lacustrine formations. The lake, which is presently extinct, reached a maximum area of about 1 km2 and a depth of 8-10 m during highstands. The Pezza Plain lake would have had five periods of maximum level, Le.: i) in an unspecified time preceding the Last Glacial Maximum; ii) during the Last Glacial Maximum, when it reached the sill level and outflowed toward Altopiano delle Rocche; iii) during a period from about 5,790±70 to 3,240±65 years B.P.; iv) during a period much more recent than 3,175±65 B.P. and older than 1,575±65 years B.P.; v) in a period after 1,575±65 years B.P. and before 926±40 years B.P. The lake level was low up to dry in the intervals between these periods. It is probable that the lake disappeared for a certain time, at least from 3,240±65 to 3,175±65 years B.P. when the only eolian sediments recognized in the sedimentary series were deposited. At about 3,400±50 years B.P., in the western portion of the Pezza Plain, another ephemeral short-living lake of small area formed due to the damming action of detrital and colluvial deposits. Lake level fluctuations were linked to climatic changes which modified the hydrologic equilibrium in the catchment area. Nevertheless, the periods of absence of the lake-like the present one-or of low lake levels, do not always correspond with arid climatic conditions. At present, even if there is no lake on the Plain, the mean annual rainfall is ca. 1,200-1,300 mm. With regard to the past, the development of soils-andò soils, in particular-indicates that even when the lake was low or dry, climate was not arid. Probably temperature was one of the main factors controlling the variations in the hydraulic equilibrium: elevated temperatures favour evaporation and therefore, for equal rainfall amounts , there is a decrease in lake level up to the lake drying up. Morphological stability and development of the present soil (following a phase of aridity marked by absence of the lake and deposition of detrital and colluvial deposits, which occurred during part of the Medieval period) are factors that seem to make the Pezza Plain present situation more similar to that of the time immediately before 6,090±80 to 5,790±70 years B.P. The drastic areal reduction and disappearance of the Pezza Plain ephemeral lake in the last 1,000 years, is not an isolated case: also some ephemeral lakes found on the Meta Massif at similar altitudes, have recently disappeared. Also these lakes indicate variations in the catchment areas hydraulic equilibrium such as it has been noticed for the Pezza Plain lake.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
