A.V Milkov,
Geochemical and Environmental Research Group, College of Geosciences, Texas A&M University, College Station, TX 77845, USA
Received 5 August 1999. Accepted 28 February 2000. Available online 20 June 2000.
The list of known and inferred submarine mud volcanoes is presented in this paper.
They occur worldwide on shelves, continental and insular slopes and in the abyssal parts of inland seas. Submarine mud volcanoes are distributed on the Earth more extensively than their subaerial analogs.
The estimated total number of known and inferred deep-water mud volcanoes is 103–105. There are two key reasons for the formation of submarine mud volcanoes—high sedimentation rate and lateral tectonic compression.
Submarine mud volcanoes form by two basic mechanisms: (1) formation on the top of a seafloor-piercing shale diapir; (2) formation due to the rise of fluidized sediments along faults.
Fluid migration is critical to the formation of a mud volcano. Gas hydrates are often associated with deep-water mud volcanoes and have many common features from one accumulation to another.
Gas hydrates form by conventional low-temperature hydrothermal process around the central part of a mud volcano and by metasomatic processes at its periphery.
A preliminary global estimate of methane accumulated in gas hydrates associated with mud volcanoes is about 1010–1012 m3 at standard temperature and pressure.
Global; Mud volcanoes; Diapirs; Gas hydrates; Volume
Figures and tables from this article:
Fig. 1. Map showing the worldwide locations of onshore (1, after Rakhmanov, 1987, with additions), known (2, without gas hydrates; 3 hydrate bearing), and inferred (4) submarine mud volcanoes. The “possible sediment diapirs” mapped by Lancelot and Embley (1977) are also shown (5).
Fig. 2. Cartoon showing submarine mud volcanoes formed by two basic mechanisms: (A) seafloor-piercing shale diapir without a mud volcano; (B) a mud volcano formed on top of a seafloor-piercing shale diapir; (C) a seafloor seepage; (D1, D2) mud volcanoes formed due to the rise of fluidized sediments along faults. Arrows show the migration paths of fluids.
Fig. 3. Cartoon showing the proposed model of the formation of gas hydrates within a mud volcano: (a) hydrothermal process dominates around the central part of the mud volcano; (b) metasomatic process dominates at the peripherical part of the mud volcano. See text for details.
Table 1. Summary of known submarine mud volcanoes
Table 2. Summary of inferred submarine mud volcanoes
Mud volcanoes occur worldwide in areas of rapid sedimentation, lateral tectonic compression, and geologically recent magmatic activity.
The total number of individual mud volcanoes on the Earth exceeds 2,000 and this number is growing as the exploration of deep oceans continues.
Sediments and fluids expelled from mud volcanoes provide useful information on the geology and petroleum potential of deep sedimentary basins.
Mud volcanoes are considered to be a minor but yet not fully recognized and properly quantified source of greenhouse gases (mainly methane) in the atmosphere.
A significant (but still uncertain) amount of methane may escape into the ocean and affect the size and characteristics of the ocean carbon pool. Finally, mud volcanoes represent a recognized geohazard that affects life forms and petroleum exploitation.
This paper reviews the results of recent studies into worldwide mud volcanism.