Jökull - 01.06.2000, Page 4

Eysteinn Tryggvason
Figure 1. Ground deformation according to the Mogi model where a small spherical body at 5 km depth (bottom)
expands, causing 1.0 m maximum uplift. Top graph shows the vertical surface displacement and how it varies
with horizontal distance from the expanding sphere. Center graph shows the corresponding ground tilt, positive
if up towards the right, which is greatest at horizontal distance of 2.5 km, equal half the depth to the expanding
body. This model is widely used to explain and understand observed ground deformation. - Fœrsla yfirborðs
jarðar samkvœmt reiknilíkani Mogis. Lítil kúla (kvikuhólf) á 5 km dýpi þenst út þar til mesta landris er einn
metri. Sýnt er hvernig ris (efst) og halli (í miðju) breytist með láréttri fjarlægð frá kúlunni.
will be displaced inversely proportional to the second
power of the slant distance to the central point of the
volume of increased pressure. These displacements
will cause the ground surface to tilt up towards the
volcano, if the magma reservoir beneth the volcano
is undergoing increased pressure. This tilt varies with
distance to the volcano, being greatest at a distance
equal to half the depth to the center of the volume of
pressure increase (Figure 1).
A deep magma chamber that expands will cause
2 JÖKULL No. 48