Hy
dr
ate
sta
bil
ity
zo
ne
0
Zone of gas hydrates in subsea
sediments
273
283
293
Temperature (K)
Hydrothermal
gradient
Depth/meter
500
1000
Seafloor
Zone of
Hydrate-phase
boundary
Geothermal
gradient
gas hydrates
in sediments
1500
The sediments are saturated with water.
(a)
Zone of hydrates in permafrost

263
273
283
293

0
T (K)
Geothermal gradient
Permafrost
in permafrost
Zone of
gas hydrates

in permafrost

Depth/meter
500
Depth of permafrost
Phase boundary
Geothermal
gradient
1000
1500
The sediments are saturated with water.
(b)
Methane from Gas Hydrates
331
FiGUre 12.2 (See color insert.) Gas hydrate stability fields for (a) n ominal marine settings
and (b) permafrost settings. (From Tohidi, 2013, pers. comm. With permission.)
in Table 12.1 [1,60] (Tohidi, 2013, pers. comm., numerous works of Collet and
coworkers at USGS). These data clearly show the dominance of gas hydrates as a
source of carbon.
Types of methane hydrate deposits found on this earth are graphically illustrated in Figure 12.4 (Methane hydrate…, 2013, pers. comm.). Methane hydrates