The structure and the evolution of the Podmoskovnaya Cave

In February 2020 a new Podmoskovnaya karst cave was discovered near the Novlenskoe village to the south from Moscow. The cave is considered to be the longest natural cave in the Moscow Region and among the longest ones in Central Russia. The specific value of the cave is its type and origin, i.e. rare and insufficiently explored Russian karst type (also known as closed, deep-seated, or confined karst). The laying depth of the cavity is 18 m; it lies in the Middle Carboniferous limestones, covered by Jurassic clay. The results of the cave examination performed with the manual widening of underground passages, are presented, namely the description of the cave and its sediments, its topographic plan and surface reference with accuracy about 5 m spatially and 1 m vertically. The Podmoskovnaya cave is a typical “flood labyrinth” (irregular in the plan) and consists of two cave levels connected by karst wells 2,5-3 m high. The length of already mapped passages is more than 190 m. Our investigation also reviews the detailed history of cave formation, i.e. hydrological and paleogeographic conditions, and specific features of cave sedimentation. Karst processes in the Podmos-kovnaya cave were syngenetic with incision/aggradation rhythms. The cave age was determined using the geomorphologic correlation; the main cavities were formed about 115-130 ka BP (MIS 5e; the Eemian). The Pakhra River discharged through the Podmoskovnaya Cave into the depths of a rock massif with typical velocity of 1-5 cm per second. About 40-115 ka BP (MIS 5d - middle of MIS 3; the first half of the Last Glacial Period) the velocity of underground flow was significantly lower (about 0.1-0.2 cm per sec). This resulted in the deposition of laminated silty clay, which was mostly taken from the upper layers. The water left the cave about 40 ka BP, almost instantly in geological terms.

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