G
Gas
(see volatile; water )
noncondensible (see carbon dioxide )
Gauro Yellow Tuff, Italy 166
Geobarometer 311 , 377
Geochemistry
(see chemical processes, hydrogeochemistry )
Geomorphology
(see also landforms )
constraints 5
Geothermal
(see also hydrothermal )
energy 1 -5
exploration (prospecting) 1 -5, 95 , 295
gradient (see thermal gradient )
heat
conversion to electricity 354 -355
reservoir 4
depth 89 -95, 154 -160, 243 -245, 246
development 171
geometry 89 -95, 159 -160, 243 -245, 250 -251
potential 16 , 115 , 171 , 246
pyroclastic deposits 89 -95, 159 -160
resource
magnitude 42 -50, 171
production 46 -47, 171
systems
caldera 159 -160
basaltic volcanoes 225 -259
hot-dry rock 160
hot water 119 , 160
surface manifestations 119 -140, 159 -162
vapor-dominated 120
well (see well )
Geothermometer 311 , 377
Geovolcanology (see volcanology )
Geyser
eruption 120 -121
Old Faithful, Wyoming 120 -121
Glass
(see also pyroclastic rocks )
alteration 94
chemical variations 70
hydration 70
palagonitization 70
basaltic 70
devitrification 187
refractive index 339
silicic 94
solution 131 , 135
Glomeroporphyritic 377
Gradient
pressure 88
thermal 51
Grain (clast)
shape 320
size (see granulometry )
texture 320 , 326
Granulometry (grain-size distribution) 8 , 303 , 312 -320, 377
basalts 67
class-size intervals 314
classification 21 -22, 312 , 340 -341
dome tephra 185
economic significance 90
hydrovolcanic (hydroclastic) 67 -68
interpretation 18 , 312 -316
log-normal distribution 312
median diameter 314 , 316 , 318
Mount St. Helens 67 , 320
rhyolites 60 , 67
sequential fragmentation/transport 315 -320, 322
sieving 312
size-frequency distribution 60
Crater Elegante, Mexico 320
Fogo A tephra, Azores 318 , 323
Mount St. Helens 320
Vesuvius, Italy 321
sorting 312 , 319
subpopulations 315 , 320 -321
Vulcano 67
Wairakei Formation 60
Gravitational slumps
Hawaii 226
Réunion Island 255 -259
Groundmass 377
Ground surge (see pyroclastic surge )
Ground tilt 97 , 102 , 107 , 108
Groundwater (see water )