![Sample our Geography journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/5937/TOC-Subject-Sample-2021-Geography.jpg"})
Abstract
Differences in permeability, parallel versus perpendicular to bedding, in e.g. a stratovolcano, direct the major part of the ground water flow to the near‐surface deposits, where it may be collected in local, perched aquifers. Percolation of meteoric water down to the basal ground water aquifer is slow, but is enhanced by steep fault surfaces and dykes. In much of the present literature in hydrogeology it is assumed that the ground water flow takes place by seepage, if tunnels such as lava tubes are not available. The presented data, from the slopes of Tenerife and a table mountain, Bläfjall, in northern Iceland, demonstrate that ground water flow is able to create its own tunnel network in the near‐surface deposits of a volcano slope in order to enhance the drainage of the meteoric recharge. As the volcano grows, new tephra beds are deposited on top of the older units and a new gallery of tunnels will probably be formed in the new near‐surface deposits. The older galleries receive less water and the tunnels are filled by stratified subsurface sediments; eventually the tunnels will become abandoned. The ground‐water tunnels are a part of the regulating system enhancing the drainage of a volcano; they also contribute to the erosion of the volcano. Volcanoes are important aquifers in different parts of the world and are used as reservoirs for drinking water and irrigation. A ground‐water tunnel system preferentially drains the perched aquifers and as such their role is in conflict with the interests of the users of ground water. On the other hand, they prevent overflow in the perched aquifers, which otherwise might release devastating debris‐flows down the volcano slopes.
Kumpulainen, R.A., 1997: Subsurface sediments tell about the hydrology of a volcano. GFF, Vol. 119 (Pt. 2, June), pp. 135–139. Stockholm. ISSN 1103–5897.