Spring may see more sinkholes2014-02-04
Karst processes, in particular the formation of sinkholes and depressions, have a long history in Pasvalys and Biržai districts. Sinkholes damage roads and buildings and cause problems to farmers.
The Lithuanian Geological Survey takes part in the implementation of the Environmental Monitoring Programme and, in cooperation with scientists from the Nature Research Centre and employees of Biržai Regional Park, monitors the karst process and measures its intensity (the scale of gypsum dissolution or denudation). It also accounts for and measures sink-holes.
Tests have shown that in 2013 the quantity of dissolved gypsum in the karst region exceeded the average multi-annual figures. The more intensive dissolution of gypsum is associated with climate change.
2013 was warmer by almost 1 degree
The average annual temperature in 2013 was relatively high: from January through November the temperature was by 0.9 degree higher than the multi-annual average. Temperatures in the warm season were especially high. In June, temperatures exceeded this month’s average multi-annual figures by as many as 3.9 degrees.
Such high temperatures of the warm season and the relatively low rainfall in July (by 29 per cent lower than the monthly average) and August (by 59 per cent below the monthly average) determined the fall of the groundwater level in the cavernous rock system. This was also indicated by the especially low level of the karst lakes at the end of autumn.
Favourable conditions for sinkholes developed
According to the fluctuations of the water level in the karst lakes (Lake Pelanis in Kirkilų village), in 2013 the annual range of water level change was 1.93. The maximum and minimum water levels were observed on 19 April and 22 November respectively.
Last year, the highest and lowest water levels for the period 2010 to 2013 were recorded. The large annual range of water level fluctuations and the relatively low minimum level may create more favourable conditions for increased karst denudation. This means that more dissolved gypsum may lead to a larger number of karst sinkholes next spring.
Sinkholes are most likely to occur in spring and autumn
The systematic recording of new karst processes for almost two decades has revealed some regularity: most of them develop in the spring and autumn months.
In May and November 2013, two research tours were organised to the karst region of Northern Lithuania. Last year, the most impressive karst sinkhole measuring 8 m in width and 9.5 m in depth opened in Trečionys, Naradava Orchard, about 40 m from the road Pasvalys-Biržai.
Earlier that spring an insignificant depression on the earth surface had been noted which in late April developed into a deep sinkhole in the form of a well. About two weeks later, employees of the Directorate of Biržai Regional Park measured this karst phenomenon (sunken apple trees were floating on the bottom, and the distance from the earth surface to the water amounted to 7.2 m). A karst sinkhole of this size develops every 3 to 5 years.
New sinkholes of average size have been found in Biržai district (3.3 m wide and about 1 m deep in Padaičių village, and 5.5 m wide and 4.0 m deep in Kirkilai). Other small depressions appeared on the fields of the villages of Karajimiškis, Daumėnai, Latveliškis, Kirkilai and Biržai.
The land of Karajimiškio village is also of interest due to its abundant caves and crevices. A horizontal cave was discovered in the wall of a shallow depression, 7 crevices were found in the territory of the former Šventoji Cave and a few more karst holes and caves were detected on the bottom of the shallow Požemis Stream.
Data on new karst processes are collected during both scheduled trips to the karst region and close cooperation with employees of the Directorate of Biržai Regional Park and specialists of the municipal administrations. This information is stored in the subsystem of Geological Processes and Phenomena of the State Geological Information System GEOLIS. In 2013, information on 48 karst phenomena was collected and systematised, while the area covered by sinkholes in the karst territory increased insignificantly.
Public Information Division