Glacial sandurs are an as yet largely unexplored groundwater environment, which could contain large volumes of water that could be a useful resource in many areas. A sandur is a flat plain spreading out in front of a glacier, made up of unconsolidated and generally coarse-grained and probably highly permeable sediment that’s been washed down by meltwater.
The observatory at Virkisjókull, which is collecting extensive data on climate, ice and river dynamics, provides an excellent opportunity to start investigating sandur hydrogeology, and the kinds of changes that could be expected as glaciers retreat.
In 2012, work is underway at Virkisjókull to try and answer questions such as:
In order to study the groundwater in detail, we’ve drilled eight shallow boreholes — between 8 and 15 m deep — into the Virkisjókull sandur, and started to test them to investigate aquifer properties, groundwater hydraulics, and groundwater chemistry and residence time.
While the boreholes were being drilled, we had a great opportunity to collect samples of the sandur sediments, to help in understanding the flow of groundwater.
Since the drilling finished, we’ve been test pumping the boreholes to establish aquifer hydraulic properties, which has already confirmed that the sandur is highly permeable with large volumes of groundwater storage.
We’re also installing loggers in the boreholes to monitor groundwater levels, temperature and water conductivity throughout the year.
Next we’ll be collecting groundwater samples from the boreholes for chemical and stable isotope analysis, to try and understand more about the source and travel time of the groundwater.
Alongside the boreholes, we are surveying the sandur to observe where groundwater discharges naturally at the ground surface as springs, and hand-installing some shallow piezometers to expand the amount of data we can collect on groundwater levels.
We’re also investigating how permeable the surface sediment is, to establish how much water could be recharging to the aquifer through the river channel bed and across the sandur from rainfall.
Already we’re starting to understand more about the complex hydrological system of the sandur. The hydrogeological principles which govern groundwater-surface water interaction in temperate climates don’t apply here.
Early results suggest that the hydrological system — including groundwater levels, recharge, residence times and chemistry — is strongly influenced by glacial melt rates, which are in turn controlled largely by temperature.
We’re already seeing some evidence that the meltwater river could be a significant control on groundwater, possibly providing recharge to the aquifer close to the river, and maybe impacting on groundwater levels even quite far from the river.
For example, as the river level dropped in late August 2012, as temperatures cooled and reduced the rate of glacial melting, groundwater levels in the sandur appeared to drop in response — with the greatest groundwater level fall happening closer to the river, and the smallest fall further away from the river.
As we continue to carry out tests and collect more information, these relationships will start to become clearer, so that we can start answering those questions.