Thermal water resources in Hungary, their utilisation and protection

GEOTHERMAL CONDITIONS IN HUNGARY

Geothermal gradient in Hungary is 5 o C/100 m as an average, which is about one and a half times as high as the worldwide average. The reason is that in the Pannonian basin including also Hungary, the earth’s crust is thinner than the worldwide average (as thick as only 24/26 km, which is thinner by about 10 km than in the neighbouring regions) thus the hot magma is nearer the surface, and the fact that the basin is filled with deposits of good heat insulation (clays and sands). The measured value of heat-flux is also rather high (the average of 38 measurement is 90,4 mW/m 2 while the mean value in the European continent is 60 mW/m 2 ).

The mean temperature is about 10 o C on the surface and with the above mentioned geothermal gradient the rock temperature is 60 o C at the depth of 1 km and 110 o C at the depth of 2 km together with the water contained by them. The geothermal gradient is higher than the countrywide average in the southern part of the Transdanubian region and in the Lowland, while it is lower in the Kisalföld region and in the hilly areas of the country. The greatest depth of the investigated aquifers of good transmissivity is 2,5 km. Temperature here is already as high as 130-150 o C.

However the water proceeding upwards in the thermal wells cools down, thus the temperature of the water on the surface exceeds the 100 o C in a few cases only. Steam occurrences are known only in a few not well investigated explorations of great depth. As far as the geothermal steam occurrences of high temperature are concerned, Hungary is not in such a favourable situation than the countries characterised by active volcanism (e.g. Iceland, Italy, Russia (Kamchatka) etc.).

In Hungary the wells and springs of higher than 30 o C wellhead water temperature are considered as geothermal wells or geothermal springs (thermal waters). Waters of such temperature can be explored on the 70 % of the area of the country from the known geological formations.