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Bubble-induced cave collapse.

Girihagama L, Nof D, Hancock C - PLoS ONE (2015)

Bottom Line: Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters.Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a "collapse".In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.

View Article: PubMed Central - PubMed

Affiliation: Geophysical Fluid Dynamics Institute, The Florida State University, Tallahassee, Florida, United States of America.

ABSTRACT
Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned "natural" instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a "collapse". We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.

No MeSH data available.


Related in: MedlinePlus

Florida map.A map showing the approximate locations of the Jackson Blue Springs, Indian springs, Wakulla Springs, and the Peacock Springs. See text for a discussion of these springs. Information taken from Esri, DeLorme, USGS, NPS / Esri, GEBCO, DeLorme, NaturalVue / Esri, GEBCO, IHO-IOC GEBCO, DeLorme, NGS.
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pone.0122349.g001: Florida map.A map showing the approximate locations of the Jackson Blue Springs, Indian springs, Wakulla Springs, and the Peacock Springs. See text for a discussion of these springs. Information taken from Esri, DeLorme, USGS, NPS / Esri, GEBCO, DeLorme, NaturalVue / Esri, GEBCO, IHO-IOC GEBCO, DeLorme, NGS.

Mentions: In contrast to most aquifers in the world (consisting of a continuous and relatively uniform porous media), the Florida aquifer is a mixture of tunnels and a continuous matrix, usually referred to as a “karst” aquifer (Figs 1 and 2). Such an aquifer looks like “cheese” in the sense that it contains both tunnels (a few meters in diameters as shown in the left panel of Fig 2) and a porous limestone medium whose particles have a scale of a millimeter or less (Fig 2, right panel). (The name “karst” originates from the German name for “Kras”, a region in Slovenia where the first scientific research of karst topography was made.) Karst caves are formed by groundwater gradually dissolving the surrounding limestone such that their size is constantly growing.


Bubble-induced cave collapse.

Girihagama L, Nof D, Hancock C - PLoS ONE (2015)

Florida map.A map showing the approximate locations of the Jackson Blue Springs, Indian springs, Wakulla Springs, and the Peacock Springs. See text for a discussion of these springs. Information taken from Esri, DeLorme, USGS, NPS / Esri, GEBCO, DeLorme, NaturalVue / Esri, GEBCO, IHO-IOC GEBCO, DeLorme, NGS.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4388830&req=5

pone.0122349.g001: Florida map.A map showing the approximate locations of the Jackson Blue Springs, Indian springs, Wakulla Springs, and the Peacock Springs. See text for a discussion of these springs. Information taken from Esri, DeLorme, USGS, NPS / Esri, GEBCO, DeLorme, NaturalVue / Esri, GEBCO, IHO-IOC GEBCO, DeLorme, NGS.
Mentions: In contrast to most aquifers in the world (consisting of a continuous and relatively uniform porous media), the Florida aquifer is a mixture of tunnels and a continuous matrix, usually referred to as a “karst” aquifer (Figs 1 and 2). Such an aquifer looks like “cheese” in the sense that it contains both tunnels (a few meters in diameters as shown in the left panel of Fig 2) and a porous limestone medium whose particles have a scale of a millimeter or less (Fig 2, right panel). (The name “karst” originates from the German name for “Kras”, a region in Slovenia where the first scientific research of karst topography was made.) Karst caves are formed by groundwater gradually dissolving the surrounding limestone such that their size is constantly growing.

Bottom Line: Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters.Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a "collapse".In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.

View Article: PubMed Central - PubMed

Affiliation: Geophysical Fluid Dynamics Institute, The Florida State University, Tallahassee, Florida, United States of America.

ABSTRACT
Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned "natural" instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a "collapse". We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.

No MeSH data available.


Related in: MedlinePlus