G
Gas
(see volatile; water )
noncondensible (see carbon dioxide )
Gauro Yellow Tuff, Italy 166
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
systems
caldera 159 -160
basaltic volcanoes 225 -259
hot-dry rock 160
surface manifestations 119 -140, 159 -162
vapor-dominated 120
well (see well )
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
Glomeroporphyritic 377
Gradient
pressure 88
thermal 51
Grain (clast)
shape 320
size (see granulometry )
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
log-normal distribution 312
median diameter 314 , 316 , 318
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
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 )