Interactions between hotspot, rift and cryosphere: the natural laboratory in Iceland

Iceland is a unique example for studying the interaction between a mantle plume, an active oceanic rift (Mid-Atlantic ridge) and icecaps, like Vatnajökull, the largest glacier in Europe. Vatnajökull is undergoing fast volume decrease, which is likely accelerated nowadays, due to global climatic change. Because of its particular location above the axis of the active rift, the Vatnajökull glacier is also subject to major magmatic events. Rapid uplift (> 1 cm/yr) is now observed all around the glacier and could be due tu unlaod related to accelerated ice melting. The main questions addressed in this research programme are:

• Is the present day uplift observed around Vatnajökull only due to the ice melting and unloading?
• How far did the deep-seated phenomena (magmatism and volcanism) that affect the Earth’s surface through volcanic eruptions and earthquakes influence the behavior of a major glacier such as the Vatnajökull? Do these changes significantly affect the conclusions that may be drawn from glacier variations in terms of climatic evolution?
• Did, in turn, the evolution of the glacier exert some control on the tectonic and magmatic evolution underneath, in terms of fissure swarm behavior and dyke injection?
• What is the impact of disastrous phenomena, as deduced from the past history and inferred from modeling for the future?

Campaign 2012

Year 4/4

IPCROCI-2
Field work project
WP 1 : Present Day deformation
2012 is a key year for WP1. During the 2012 campaign we plane to remeasure all GPS point measured in 2010. These points are distributed all along the southern part of the Vatanajökull area (Figure 1). The aim of this campaign is to analyze the spatial distribution of the deformation at the Vatnajökull margin. We benefit of a network of benchmarks already installed and measured in the three times or more (in addition of our 2010 measurements). Oldest measurements are from 1996. Most of the points have been observed at least once since 2000. Last complete measurement in the area has been made in 2004 (Pagli et al. 2007). We will concentrate our efforts on studying the variation of vertical uplift rate with the distance to the center of the ice cap. The wavelength and maximum amplitude of the uplift will be better constrained by this new set of data. For the comparison with old sets of measurements, we have access by the way of our collaboration with E. Sturkell (Gothenburg Univ., Sweden) to data collected in this area (e.g; data published by (Pagli et al. 2007)). We know from the last campaign that a few points require very high clearance vehicle that could not be rented from local rental car companies (eg points SLET and HAOX). For the points we will rent the services of mountains guide company to access these points securely.
Velocities vary from 9 to 20 mm/yr with uncertainties between 2–4 mm/yr. Gray bar shows inferred 95% confidence interval. Overlaid is the outline of the Öraefajökull central volcano (solid line) and its caldera (dashed line).
In addition data at CGPS sites (SKRO, GFUM, KVSK and now EYVI, see 2011 campaign report for more detail) will be collected and carefully analyzed
WP2 : Present Day seismicity below and at the margin of Vatnajökull This Workpackage do not require any field work.
WP3 : Interaction between structure, magmatism, tectonism and glacier We do not plan any field work for WP3. Romain Plateaux (Univ. Nice) will have collected the last data for his phD during this summer. He will be finishing the writing his thesis during the next summer.
WP4 : Deglaciation and jökulhlaups

A) Jokulhlaups
Continuation of the analysis of stratigraphic sequences at the West of the Vatnajökull , with a special attention for the Holocene events and there recurrent character. The field targets will be mostly located in central Iceland, upstream of the former observations.The field data will be combined with aerial photos analysis, focusing on lava flow from which the age is known to locate the stratigraphic position of the channel incision events. About 10 sections need to be analyzed between the south of Thorisvatn and Hagongulon. Continuation of the cartography of glacially dammed paleolakes observed in this zone in 2009 and 2011 and analysis of the morphological traces of jökulhlaup outflows.
• A prospection (field + geochemistry) for material issued from a subglacial volcano as the Bardarbunga and Hammarin ‐Veidivton in collaboration with Gilles Chazot (DO, geochemistry, tephra). The last important eruption of the Bardarbunga dates back to 1917, but its activity is interconnected with these of the Grimvotn volcano. The 1776 eruption generated a jökulhlaup that followed the Thjorsa River instead of the Jökulsa a Fjöllum (Steinthórsson, 1977). Dating the major Holocene eruption of the Bardarbunga volcano is of prime order as this eruption is presumed responsible for the formation of the caldera and one of the 2 Holocene megajokulhlaups. It is possible that the 2900 BP jökulhlaup event could be attributed to this volcano. A brief prospection of 2 days is scheduled along the Jökulsa a Fjöllum to analyze the functioning of jökulhlaup in a constrained system compared to the Thjorsa‐Ytri Ranga braided system.

B) Volcanoe dating.
The sampling campaign to date the subglacial volcanoe’s will also continue in 2012 along the NW margin of the Vatnajökull (the Eastern has been sampled in 2009) and the Tungafell, as also thelowermost Askja structure. It seems important to compare the date of volcanic initiation on the SWVZ with the Eastern part of the Vatna (sampled in 2009) with the rise in activity of this branch of the Icelandic rift. North and South SWVZ seem to develop simultaneously and not to propagate to the South.

References
Pagli, C., Sigmundsson, F., Lund, C., Sturkell, E., Geirsson, H., Einarsson, P., Árnadóttir, T. & Hreinsdóttir, S. 2007. Glacio‐isostatic deformation around the Vatnajökull ice cap, Iceland, induced by recent climate warming: GPS observations and Finite Element Modeling. J. Geophys. Res. 112 (B08405).

Campaign 2011

Year 3/4

The main objective of the 2011 field trip is to study the western edge of the Vatnajökull. We have in this area Continuous GPS recording since 2000. This area is under uplift at a rate of 26mm/yr. Main work in the field will be devoted to tectonic studies on active fissure swarms and identification of old Jokulhlaup traces.

Campaign 2010

Year 2/4

In 2010 we plane to carry out a GPS campaign around, at least the southern part of the Vatanajökull area. The aim of this field work is to analyze the spatial distribution of the deformation around Vatnajökull. We benefit of a network of benchmarks already installed and measured several times since 1996. In addition the collection of data at CGPS sites (SKRO, GFUM and now KVSK) and semi continuous sites (EYVI and ESJU) will be maintained.

Fault and fissure detailed mapping will be carried out on fissures swarms located southwest of Grimsvötn, between Ljosufjöll andGrænafjall and in the ice-freedomain between Vatnajökull and Mýrdalsjökull. A special attention will be paid to Lakagigar because its huge fissural eruption (1783-1784) need to be more understood in terms of interaction beween volcanism and ice cap.

We also plane to work on river sections in the Estry Ranga, Fiska, lower Markarfljot, Tungnaa and Thjórsa (around Thorisvatned) valleys to define the timing and the origin of Holocene jökulhlaups. The aim is to determine the altitude of flooded surface to define a maximal pick of discharge and to find dating criteria (tephra, buried soils) for the main events.

Campaign 2009

Year 1/4

- Study of fractures networks located in the area of Laki, where there was a gigantic fissure eruption in the late 18th century.
- Mapping of jökulhlaup traces in watersheds: sections collection to constrain the chronology and source of Holocene jökulhlaup in order to determine in each site the level of the flooded area to assess the intensity of flood peak and find criteria for dating.

Cf. at the right IPCROCI-1 (2006-08) description