Cavern Collapse Research Articles

Paleocollapse structures as geological record for reconstruction of past karst processes during the Upper Miocene of Mallorca Island

Paleocollapse structures and collapse breccias are one of the major features for paleokarst analysis and paleoclimate record. These are affecting the Llucmajor and Santanyí carbonate platforms. These platforms, of southern and eastern Mallorca respectively, are a good example of progradation reef platform in the western Mediterranean. The Santanyí platform is constituted of two sedimentary units, both affected by paleocollapse structures: (1) The Reef Complex attributed to the upper Tortonian-lower Messinian; (2) Santanyí Limestone attributed to the Messinian. There are abundant paleocollapse outcropping in the Reef Complex and Santanyí Limestone units. These structures have been produced by roof collapse of caverns developed in the underlying reefal complex. According to the genetic model, the origin of same paleocollapse structures may be related to early diagenetic processes controlled by high-frequency sea-level fluctuations. During the lowstands of sea level, fresh water flow or mixing zone might have created a cave system near the water table by dissolution of aragonite in the reef front facies and coral patches existing in the lagoonal beds. During subsequent rise and highstands of sea level, inner-shelf beds overlaid the previously karstified reef-core and outer-lagoonal beds. Increase of loading by subsequent accretion of the shallow-water carbonate might have produced paleocollapse structures by gravitational collapse of cave roof. Morphometric and structural classification of paleocollapse is based on geometric and structural criteria according to the type of deformed strata and strata dip. Paleocollapse structures can be classified according to geometric section, size of the paleocave and lithification degree of the host rock when collapsed. Breccias are classified as crackle, mosaic and chaotic types. In same paleocollapse the type of breccias present a vertical and lateral gradation, from crackle in the upper part, to chaotic in the lower part of the paleocollapse. Chaotic breccias grade from matrix-free, clasts-supported breccias to matrix-supported breccias. Relationship with high frequency of sea-level fluctuation, facies architecture, classification features and products permit to enhance a general paleoclimatic framework.

Gravity changes and passive SO 2 degassing at the Masaya caldera complex, Nicaragua

An understanding of the mechanisms responsible for persistent volcanism can be acquired through the integration of geophysical and geochemical data sets. By interpreting data on micro-gravity, ground deformation and SO 2 flux collected at Masaya Volcano since 1993, it is now clear that the characteristically cyclical nature of the activity is not driven by intrusion of additional magma into the system. Rather, it may be due in large part to the blocking and accumulation of gas by restrictions in the volcano substructure. The history of crater collapse and formation of caverns beneath the crater floor would greatly facilitate the trapping and storage of gas in a zone immediately beneath San Pedro and the other craters. Another mechanism that may explain the observed gravity and gas flux variations is the convective overturn of shallow, pre-existing, degassed, cooled, dense magma that is replaced periodically by lower density, hot, gas-rich magma from depth. Buoyant gas-rich magma rises from depth and is emplaced near the surface, resulting in the formation and fluctuation of a low-density gas-rich layer centred beneath Nindirı́ and Santiago craters. As this magma vigorously degasses, it must cool, increase in density and eventually sink. Five stages of activity have been identified at Masaya since 1853 and the most recent data suggest that the system may have been entering another period of reduced degassing in 2000. This type of analysis has important implications for hazard mitigation because periods of intense degassing are associated with poor agricultural yields and reduced quality of life. A better understanding of persistent cyclically active volcanoes will allow for more effective planning of urban development and agricultural land use.

Single-force representation of earthquakes due to landslides or the collapse of caverns: Y. Fukao, Geophysical Journal International, 122(1), 1995, pp 243–248

Single-force representation of earthquakes due to landslides or the collapse of caverns: Y. Fukao, Geophysical Journal International, 122(1), 1995, pp 243–248

Design against collapse of karst caverns : T. M. Tharp, in: Karst geohazards: engineering and environmental problems in karst terrane. Proc. 5th conference, Gatlinburg 1995, ed B.F. Beck, (Balkema), 1995, pp 397–406

Design against collapse of karst caverns : T. M. Tharp, in: Karst geohazards: engineering and environmental problems in karst terrane. Proc. 5th conference, Gatlinburg 1995, ed B.F. Beck, (Balkema), 1995, pp 397–406

Single-force representation of earthquakes due to landslides or the collapse of caverns

Earthquakes due to landslides and the collapse of caverns are caused by the release of gravitational potential energy rather than elastic strain energy. Landslide (or cavern collapse) is assumed to start with dislocation motion along the lubricated interface of the slide block (or fallen block) that intersects the Earth's free surface. It can be shown that, if each component of the dislocation vector is position-independent and varies only as a function of time, the resultant static displacement is spatially uniform both inside and outside the block, and, therefore, no change occurs in static strain energy. In particular, if the medium is unbounded, the static displacement is zero outside the block. The force system equivalent to this dislocation model is a distribution of single forces equal but opposite to the dislocation acceleration multiplied by the density at each point of the volume constituting the slide block. The physics behind the equivalence is discussed. Single force appears to be a common mechanism for indigeneous earthquakes that do not change the static strain field.

Stratigraphic Geometry of Cavern Collapse and Seismic Modeling - A Predictive Tool for Exploration: ABSTRACT

Stratigraphic Geometry of Cavern Collapse and Seismic Modeling - A Predictive Tool for Exploration: ABSTRACT

Subsidence and foundering of strata caused by the dissolution of Permian gypsum in the Ripon and Bedale areas, North Yorkshire

Summary Underground dissolution of thick gypsum beds in the Edlington Formation and Roxby Formation of the Zechstein sequence in North Yorkshire, England, has resulted in a 3 km-wide and 100 km-long belt of ground susceptible to foundering. Within this belt a large subsidence depression at Snape Mires, near Bedale, was largely filled with lacustrine deposits in the later part of the Late Devensian and during the Flandrian. South of Snape Mires the Nosterfield-Ripon-Bishop Monkton area has suffered about 40 episodes of subsidence in the past 150 years, and the presence of several hundred other subsidence hollows indicates considerable activity from the later part of the Devensian onwards. The linear and grid-like arrangement of these subsidence hollows indicates collapse at intersections in a joint-controlled cave system. Linear subsidence features at Snape Mires are also joint-controlled. The transition from anhydrite at depth to secondary gypsum near surface marks the down-dip limit of the subsidence-prone belt. Cavities are propagated upwards by roof collapse of caverns in the gypsum, leading to the formation of breccia pipes. Choking of the pipes can reduce the surface expression of the underground collapse, but the larger cavities are liable to produce pipes that reach the surface even at the eastern boundary of the 3 km-wide belt described. Further subsidence in the Ripon area is predicted and some suggestions for remedial measures are given.

Gash-Breccias of South Pembrokeshire: Fossil Karstic Phenomena?

The paper records the results of mapping on a scale of I: 2500 of the gash-breccia pockets occurring within the Carboniferous Limestone Series of the Pembroke peninsula. Hypotheses for the 'derivation of these deposits through the medium of major cavern collapse or as former 'open-sky' scree accumulations are discussed. It is concluded, however, that the gash-breccias were tectonically produced in the first instance with preferential solution and limited collapse merely providing the finishing touches to the process of brecciation. It is suggested that some of the gash-breccias may be mid-Tertiary rather than Triassic in age. DURING the past two decades both geologists and geomorphologists have studied the nature and origin of the preglacial materials which occupy pipes and larger cavities, or otherwise disrupt the continuity of the normal bedded sequence, within the Carboniferous Limestone Series. Detailed surveys of such deposits have been undertaken in the Vale of Glamorgan,1 along the North Crop of the South Wales coalfield,2 in the Mendip-Bristol region,3 in north-east Wales4 and also in the Peak District.5 Perhaps the most clearly discernible deposits of this type to be found in the British Isles are the gash-breccias, long assumed to be of Triassic age, occurring within the cliff sections of the Pembroke peninsula. Here the detailed structure of individual pockets of gash-breccia is clearly revealed because of their common red-brown or pink colour, contrasting sharply with the prevalent greys of the Carboniferous Limestone. Prior to the present study no detailed examination of these gash-breccias had been made since that of E. E. L. Dixon on behalf of the Geological Survey.6 Dixon postulated that the gash-breccias had been derived by the solvent action of underground waters and the subsequent partial filling of caverns in the Carboniferous Limestone by the collapse of their walls and roofs. This view has been widely quoted by later writers, for example, by J. Pringle and T. N. George7 and J. Challinor.8 In the following account, Dixon's hypothesis is questioned; after considering other possible origins, it is suggested that the gash-breccias are in large measure of tectonic origin. Solution appears to have been preferentially concentrated along distinct shatter belts or at nodal intersections of fractures. While many of these disturbed zones are a direct result of the Armorican orogeny and were subsequently subjected to solution with some minor degree of collapse during Permo-Triassic times, others seem to be of later date and possibly of mid-Tertiary age. GEOLOGICAL BACKGROUND The gash-breccias of south Pembrokeshire are found only within the Carboniferous Limestone Series of the Pembroke peninsula and its outlying islands; they have not been recorded in the narrow outcrop of this formation which fringes the northern limits of the

The origin and development of surface depressions in the Mendip Hills

This study aims to provide a systematic classification of the numeroustypes of sinkhole mentioned in the morphological literature. As three types of stream sink are readily identifiable from their morphologicalrelationship with a valley, the main part of the investigation is concentrated upon enclosed circular depressions of other origin. Two hypotheses, formation by surface solution and formation by collapse into underground cavities, were tested in the Mendip Hills. No evidence has been found to support the idea that surface solution can form circular sinkholes. Collapse sinks of different forms have been arranged in a developmental sequence.The four stages of the karstic cycle have been redefined, coupling the same visual criteria as used before with a new rationale of process and development. This rationalised version of the karstic cycle suggests that Cheddar Gorge is more likely to have originated as a surface valley than by the collapse of underground caverns.

Swallow Holes on the Millstone Grit and Carboniferous Limestone of the South Wales Coalfield

SWALLOW holes or depressions caused by the collapse of underlying caverns are characteristic f ar as underlain by calcareous beds. The junctions of essentially calcareous formations and overlying systems of sharply contrasting lithological character have frequently been described as showing a profusion, or concentrated alignment, of swallow holes or allied forms.1 These generally mark the disappearance points of surface streams into underground courses so that the holes themselves are more attributable to the solution and enlargement of joint planes than to the collapse of pre-existing caverns. Outcrops of looselycompacted arenaceous beds forming cappings to underlying massive calcareous beds are liable to show surface reflections of the caving in of cavern roofs. It is thus normal, especially in areas with horizontal or gently-tilted strata, to find a fair scattering of these depressed features even though the top of the calcareous, cavern-bearing beds is at depths up to 30 or 40 feet. On the North Crop of the South Wales Coalfield, where comparatively narrow and roughly concentric outcrops of Millstone Grit and Carboniferous Limestone consecutively fringe the productive Coal Measures, an apparently anomalous state of affairs exists which appears to be unique. Here the most conspicuous and perfectly developed collapse features, in the form of large swallow holes, are decidedly more numer? ous on the outcrop of the Basal Grit, the lowest sub-division of the Millstone Grit, than on the outcrop of the underlying Carboniferous Limestone within whose beds such features were initiated. At certain points some of these swallow holes are located at distances of more than a mile south of the junction with the Carboniferous Limestone and underlain by a maximum thickness of about 250 feet of Grit beds. To illustrate fully this abnormal development a detailed six-inch survey was undertaken of the distribution of swallow holes and other solution sub? sidence phenomena on the Carboniferous Limestone and Millstone Grit out? crops ranging over a west-east length of 30 miles from the Twrch valley in south-east Carmarthenshire to Blorenge Mountain in north-west Monmouth shire and with a maximum north-south width of 5 miles. The results of this survey have been compounded (Fig. 1) so as to provide in one diagram a distribution picture for the region as a whole. It has revealed a wider acreage more closely pocked with swallow holes than in any other area of the British Isles. Certain sections of this area of survey, where they portray typical or special features of the distribution pattern, have been retained on a larger scale (Figs. 2 and 3). (For Fig. 1 see facing p. 474.) For the most part the Carboniferous Limestone within the limits defined has a vertical thickness of 500 to 700 feet, but in the extreme east there is a rapid diminution so that on Blorenge Mountain it is rather less than 100 feet thick.2