01630nas a2200253   4500000000100000000000100001008004100002260001500043100002100058700001600079700001800095700001700113700001500130700001800145700001800163700001700181700001900198700001900217245004500236856005700281300001200338490000700350520101900357       2005                            d  cJune, 20051 aBernard Boudreau1 aChris Algar1 aBruce Johnson1 aIan Croudace1 aAllen Reed1 aYoko Furukawa1 aKelley Dorgan1 aPeter Jumars1 aAbraham Grader1 aBruce Gardiner00aBubble growth and rise in soft sediments  uhttp://geology.gsapubs.org/content/33/6/517.abstract  a517-5200 v333 aThe mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance. We offer definitive evidence on the mode of bubble formation in the form of X-ray computed tomographic images and comparison with theory. Natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids (disks) that grow either by fracturing the sediment or by reopening preexisting fractures. In contrast, bubbles in soft sandy sediment tend to be spherical, suggesting that sand acts fluidly or plastically in response to growth stresses. We also present bubble-rise results from gelatin, a mechanically similar but transparent medium, that suggest that initial rise is also accomplished by fracture. Given that muddy sediments are elastic and yield by fracture, it becomes much easier to explain physically related phenomena such as seafloor pockmark formation, animal burrowing, and gas buildup during methane hydrate melting.