GSA TODAY • Radon in Water, P

Vol. 8, No. 11 November 1998 INSIDE • Field Guide Editor, p. 5 GSA TODAY • Radon in Water, p. 10 • Women Geoscientists, p. 12 A Publication of the Geological Society of America • 1999 Annual Meeting, p. 31 Gas Hydrates: Greenhouse Nightmare? Energy Panacea or Pipe Dream? Bilal U. Haq, National Science Foundation, Division of Ocean Science, Arlington, VA 22230 ABSTRACT Recent interest in methane hydrates has resulted from the recognition that they may play important roles in the global carbon cycle and rapid climate change through emissions of methane from marine sediments and permafrost into the atmosphere, and in causing mass failure of sediments and structural changes on the continental slope. Their presumed large volumes are also consid- ered to be a potential source for future exploitation of methane as a resource. Natural gas hydrates occur widely on continental slope and rise, stabilized in place by high hydrostatic pressure and frigid bottom-temperature conditions. Change in these conditions, Figure 1. This seismic profile, over the landward side of Blake Ridge, crosses a salt diapir; the profile has either through lowering of sea level or been processed to show reflection strength. The prominent bottom simulating reflector (BSR) swings increase in bottom-water temperature, upward over the diapir because of the higher conductivity of the salt. Note the very strong reflections of may trigger the following sequence of gas accumulations below the gas-hydrate stability zone and the “blanking” of energy above it. Bright events: dissociation of the hydrate at its Spots along near-vertical faults above the diapir represent conduits for gas venting. (After Taylor et al., 1997. Courtesy of W. P. Dillon, USGS.) base, weakening of sediment strength, major slumping, and release of significant quantities of methane in the atmosphere to affect enhanced greenhouse United States is on the verge of enacting a methane also occurs in hydrates, vented warming. Thus, gas-hydrate breakdown bill to promote gas-hydrate research under to shallower depths through subsurface has been invoked to explain the abrupt the aegis of the Department of Energy. Sci- conduits (e.g., MacDonald et al., 1994). nature of glacial terminations, pro- entists view gas hydrates (also known as Estimates of total hydrate volumes vary nounced 12C enrichments of the global clathrates) as potential agents provocateurs widely, but even the relatively conserva- carbon reservoir such as that during the for global climate change and continental tive estimate of Kvenvolden (1988), 104 latest Paleocene thermal maximum, margin tectonics. Politicians’ interest is Gt (gigaton) of methane carbon (1 Gt = and the presence of major slides and predicated on the premise that gas 1015 g), exceeds estimates of organic car- slumps in the stratigraphic record asso- hydrates may represent a huge untapped bon from all other sources, with the ciated with periods of sea-level low- source of energy for their constituents. exception of dispersed carbon in the stands. The role of gas hydrates in con- Natural gas hydrates (crystalline lithosphere, and is approximately double trolling climate change and slope solids composed mostly of methane and the estimate of carbon from known fossil- stability cannot be assessed accurately water) are present in marine sediments fuel sources (Kvenvolden, 1988). without a better understanding of the on the continental slope and rise (Fig. 1) Whether or not these estimates of large hydrate reservoir and meaningful esti- under the dual conditions of high hydro- amounts can be translated into a viable mates of the amount of methane it con- static pressure (>50 bar) and low ambient energy source is a crucial question that tains. Lack of knowledge also hampers temperature at the sediment-water inter- has been the focus of researchers in many the evaluation of the resource potential face (<7 °C). They also occur associated countries. The petroleum industry to date of gas hydrates, underscoring the need with permafrost and at shallower subma- has largely ignored methane hydrates for a concerted research effort on this rine depths in the high latitudes of the because of the difficulties in estimating issue of significant scientific impor- Arctic. The hydrate consists of a lattice of and extracting the resource and distribut- tance and societal relevance. water molecules enclosing gas molecules ing it to consumers. (usually methane, but also higher-order INTRODUCTION hydrocarbons), and at least three struc- Recently, politicians have joined sci- tures have been identified (e.g., Sloan, entists and engineers in their interest in 1998). Methane in hydrates is commonly gas hydrates. The 105th Congress of the of biogenic origin, but thermogenic Gas Hydrates continued on p. 2 IN THIS ISSUE GSA TODAY November Vol. 8, No. 11 1998 Gas Hydrates: Greenhouse Nightmare? Commentary .......................... 22 Energy Panacea or Pipe Dream? .... 1 June Forstrom Retires .................. 23 GSA TODAY (ISSN 1052-5173) is published monthly Field Guide Editor Named .............. 5 by The Geological Society of America, Inc., with offices at 3300 Dwornik Award ........................ 23 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box In Memoriam .......................... 6 GSA Section Meetings ................. 25 9140, Boulder, CO 80301-9140, U.S.A. Periodicals postage paid at Boulder, Colorado, and at additional mailing offices. Grants Support Research ............... 7 Call for Geology Co-Editor .............. 25 Postmaster: Send address changes to GSA Today, Member- SAGE Remarks ......................... 8 ship Services, P.O. Box 9140, Boulder, CO 80301-9140. Student Travel Grants .................. 26 Washington Report .................... 10 Copyright © 1998, The Geological Society of America, Inc. 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Written permission is required from GSA for all other forms of capture, reproduction, and/or distribution of any item in this publication by any means, including posting on authors’ or organizational Web sites, except that permission is granted to authors to post the abstracts only of their science articles on their own or their organization’s Web site providing the posting includes this reference: “The full paper Gas Hydrates continued from p. 1 Gas hydrates in marine sediments was published in the Geological Society of America’s news- have been detected since the 1970s (e.g., magazine, GSA Today, [include year, month, and page num- DISTRIBUTION AND ESTIMATES Markl et al., 1970; Shipley et al., 1979) by ber if known, where article appears or will appear].” GSA provides this and other forums for the presentation of OF GAS HYDRATES the presence of the so-called bottom sim- diverse opinions and positions by scientists worldwide, ulating reflectors (BSRs). BSRs usually The requirements for the stability of regardless of their race, citizenship, gender, religion, or polit- delineate the top of the free-gas zone that ical viewpoint. Opinions presented in this publication do not gas hydrate (low bottom water and thus may occur at or below the base of the reflect official positions of the Society. low sediment temperature, as well as gas-hydrate stability zone (GHSZ) (Fig. 1). SUBSCRIPTIONS for 1998 calendar year: Society high pressure [Fig. 2]; see also, Ruppel, A significant quantity of free gas must be Members: GSA Today is provided as part of membership 1997) are theoretically met over a high dues. Contact Membership Services at (800) 472-1988, present below the hydrate to provide the percentage of the seafloor of the conti- (303) 447-2020 or [email protected] for member- velocity contrast for a BSR, as revealed by ship information. Nonmembers & Institutions:

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