Doming of mudboil carapace surface disturbed by excavation
This sample site was excavated in a stable mudboil with a thick, sandy carapace (see image 0098). As the rigid carapace was excavated (with difficulty), the surface of the mudboil began to rise, creating a 10-15 cm-high rim, as shown, in less than 5 minutes. The dimensions of the notebook are approximately 14 cm x 24 cm. Note the lack of a soil profile and the black lichen completely covering the undisturbed surface. The angular blocks of sandy carapace beside the hole are typical of undisturbed carapace, but the propensity of the typical mudboil sediment to pass directly to a liquid state is clearly illustrated by the liquefied carapace fragments in the upper left-hand part of the photo. The raising of the excavated mudboil surface suggests that even in this area of stable mudboils, there is a certain amount of hydrostatic pressure beneath the relatively rigid carapace (which in this case is at least 50 cm thick). The saturated sediment beneath the carapace may behave as a liquid slurry under hydrostatic pressure, placing vertical pressure on the bottom of the relatively drier, rigid, carapace cap. The vertical pressure is probably one driving mechanism that causes diapirs to exploit weak points in the carapace. See detailed discussion for image 0240.
Updated 05/06/2010 AW