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Paul T. Delaney

Publications and source records attributed to Paul T. Delaney.

6 recordsLinked to original sources
USGS1993

Thermal budget of the lower east rift zone, Kilauea Volcano

The lower east rift zone of Kilauea has been the site of repeated fissure eruptions fed by dikes that traverse the depths of interest to geothermal explorations. We find that a hot-rock-and-magma system of low permeability extending along the rift zone at depths below about 4 km and replenished with magma at a rate that is small in comparison to the modern eruption rate Kilauea can supply heat to an overlying hydrothermal aquifer sufficient to maintain temperatures of about 250??C if the characteristic permeability to 4-km depth is about 10-15m2.

Conference Paper↗
USGS1990

Deep magma body beneath the summit and rift zones of Kilauea Volcano, Hawaii

A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.

Hawaii↗
USGS1983

Surface deformation in volcanic rift zones

The principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes, some of which feed fissure eruptions. Elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression. Concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift. If eruption occurs the characteristic ridge-trough-ridge displacement profile changes to a single ridge, centered at the fissure, and the erupted lava alters the local topography. A well-developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events. To investigate this process we compute the elastic displacements and stresses in a homogeneous, two-dimensional half-space driven by a pressurized crack that may breach the surface. A derivative graphical method permits one to estimate the three geometric parameters of the dike (height, inclination, and depth-to-center) and the mechanical parameter (driving pressure/rock stiffness) from a smoothly varying displacement profile. Direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation, notably normal faulting, creates discontinuities in the profile. Geological structures (open cracks, normal faults, buckles, and thrust faults) form because of stresses induced by dike emplacement and fissure eruption. Theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation.

Tectonophysics↗
USGS1981

Deformation of host rocks and flow of magma during growth of minette dikes and breccia-bearing intrusions near Ship Rock, New Mexico

We have studied a small group of minette dikes and plugs that crop out within a flat-lying sequence of siltstone and shale near Ship Rock, a prominent volcanic throat of tuff breccia in northwestern New Mexico. Seven dikes form a radial pattern about Ship Rock we describe in detail the northeastern dike, which has an outcrop length of about 2,900 m, an average thickness of 2.3 m, and a maximum thickness of 7.2 m. The dike is composed of 35 discrete segments arranged in echelon; orientation. of dike segments ranges systematically from N. 52? E. to N. 66? E. A prominent joint set strikes parallel to the segments and is localized within several tens of meters of the dike. Regional joint patterns display no obvious relation to dike orientation. Small offsets of segment contacts, as well as wedge-shaped bodies of crumpled host rock within segments mark the sites of coalescence of smaller segments during dike growth. Bulges in the dike contact, which represent a nondilational component of growth, indicate that wall rocks were brecciated and eroded during the flow of magma. Breccias make up about 9 percent of the 7,176-m 2 area of the dike, are concentrated in its southwest half, and are commonly associated with its thickest parts. We also describe three subcircular plugs; each plug is smaller than 30 m in diameter, is laterally associated with a dike, and contains abundant breccias. Field evidence indicates that these plugs grew from the dikes by brecciation and erosion of wallrocks and that the bulges in the contact of the northeastern dike represent an initial stage of this process. From continuum-mechanical models of host-rock deformation, we conclude that dike propagation was the dominant mechanism for creating conduits for magma ascent where the host rock was brittle and elastic. At a given driving pressure, dikes dilate to accept greater volumes of magma than plugs, and for a given dilation, less work is done on the host rocks. In addition, the pressure required for dike growth decreases with dike length. From numerical solutions for dilation of cracks oriented like segments of the northeastern dike, we find that we can best model the form of the dike by treating it as composed of 10 cracks rather than 35. We attribute this result to coalescence of adjacent segments below the present outcrop and to inelastic deformation at segment ends. Using a driving pressure of 2 MPa (20 bars), we estimate a shear modulus of about 10^3 MPa for the host rocks, in agreement with laboratory tests on soft shale. A propagation criterion based on stress intensity at the segment ends indicates a fracture toughness of the host rocks of about 100 MPa-m^? , a hundredfold greater than values reported from laboratory tests. Segmentation of fractures is common in many materials and has been observed during fissure eruptions at Kilauea Volcano in Hawaii. At the northeastern dike, we attribute segmentation to local rotation of the direction of least principal compressive stress. From continuum-mechanical models of magma and heat flow in idealized conduits, we conclude that magma flows far more rapidly and with less relative heat loss in plugs than in dikes. Although dikes are the preferred form for emplacement, plugs are the preferred form for the flow of magma. We present a numerical solution for volumetric flow rate and wall heat flux for the northeastern dike and find that although the flow rate is extremely sensitive to conduit geometry, the rate of heat loss to wall rocks is not. During emplacement of the northeastern dike, local flow rate increased where wall rocks were eroded and reached a maximum of about 45 times the mean initial rate, whereas the maximum rate of heat loss to wallrocks increased to only 1.6 times the mean initial rate. An inferred progression from continuous magma flow along a dike to flow from a plug agrees well with observations of volcanic eruptions that begin from fissures and later are localized at discrete vents. We

Professional Paper↗