GIANT GEYSER, UPPER GEYSER BASIN Eruptive activity since 1955 Data compiled via NPS and private recorders, and direct observations Data incorporates daylight savings–standard time adjustments Note: because there are significant differences between the “Mastiff function” eruptions as described from the 1950s versus the Mastiff eruptions in more recent years, the terminology has been changed; to wit: North function = Giant eruptions accompanied by a Mastiff eruption, usually occurring on the “marathon recovery hot period” following a long-duration Grotto eruption. South function = Giant eruptions without a Mastiff eruption, usually occurring on a hot period not directly associated with a Grotto marathon eruption. No. Date Time Interval Comments 1 9/18/63 22:00 ie ------- Observed i.e., start time approximate 2 9/09/78 16:00 ns ~5469d 18h Observed near start 3 9/27/82 12:47 ns ~1478d 20h 47m Observed within seconds of start 4 10/12/84 01:11 ie ~745d 12h 24m Observed in eruption 5 8/20/86 11:36 ~677d 10h 25m Start time exact 6 9/12/87 13:58 388d 02h 22m 7 6/28/88 21:55 290d 07h 57m 8 9/12/88 18:46 75d 20h 51m 9 12/18/88 00:36 96d 05h 50m 10 4/17/89 08:18 ie ~120d 07h 42m Observed in eruption 11 1/5-7/90 ------- ~265 days Known from observations of platform 12 1/25-27/90 ------- ~20 days Known from observations of platform 13 9/23/90 10:35 ns ~240 days Observed near start 14 9/30/90 15:25 ~7d 04h 50m 15 8/21/91 01:00 ie ~323d 9h 35m Observed in eruption 16 10/20/91 17:22 ~61d 16h 22m 17 9/24/92 13:45 ns ~339d 20h 23m Observed near start 18 12/2-6/93 ------- ~436 days Known from observations of platform 19 9/29/94 12:52 ~299 days 20 1/10-12/95 ------- ~104 days Probable but evidence controversial 21 9/25/95 15:19 ~257 days Interval assumes January eruption 22 7/31/96 17:43 310d 02h 24m 23 10/09/96 18:27 70d 00h 44m 24 10/18/96 11:11 8d 16h 44m 25 10/24/96 13:07 ie <6d 01h 56m Observed in eruption 26 11/09/96 01:11 ~15d 13h 04m 27 11/18/96 10:55 9d 09h 44m 28 1/1-3/97 ------- ~45 days Known from observations of platform 29 1/18-19/97 ------- ~16½ days Known from observations of platform 30 2/06/97 17:00 ~18½ days Start time exact 31 2/24/97 11:07 17d 18h 07m 32 3/04/97 13:57 8d 02h 50m 33 3/13/97 22:57 9d 09h 00m 34 3/23/97 07:45 9d 08h 48m 35 3/30/97 19:29 7d 11h 44m 36 4/06/97 19:32 6d 23h 03m 37 4/13/97 14:02 6d 18h 30m 38 4/23-24/97 ------- ~10d 11h Between 23:00 4/23 and 03:00 4/24 39 5/24/97 11:21 ~30d 10h 40 6/07/97 14:29 14d 03h 08m 41 7/10/97 06:06 ns ~32d 15h 37m Observed very near start 42 7/16/97 05:12 ns ~5d 23h 06m Observed near start 43 7/22/97 07:45 ~6d 02h 33m 44 8/01/97 06:34 9d 22h 49m 45 8/10/97 08:43 9d 02h 09m 46 8/24/97 12:24 14d 03h 41m 47 9/08/97 16:28 15d 04h 04m 48 9/12/97 22:16 ns ~4d 05h 48m Observed near start 49 9/16/97 06:30 ie ~3d 08h 15m Observed in eruption 50 9/19/97 22:10 ~3d 15h 40m 51 9/23/97 20:40 3d 22h 30m 52 9/27/97 11:38 3d 14h 58m 53 10/01/97 ------- ~3d 15h Between 01:30 and 04:30 54 10/06/97 15:33 ~5d 13h 55 10/9-10/97 ------- ~3d 13h Very late steam phase @06:00 56 10/14/97 07:21 ~4d 03h 57 10/17/97 16:44 3d 09h 23m 58 10/21/97 18:33 4d 01h 49m 59 10/25/97 21:17 4d 02h 44m 60 10/30/97 04:11 4d 07h 54m 61 11/03/97 03:00 ~3d 22h 45m Data through 12/12/97 ±15 minutes 62 11/07/97 17:15 ~4d 14h 15m 63 11/12/97 14:15 ~4d 21h 00m 64 11/16/97 02:00 ~3d 11h 45m 65 11/20/97 19:30 ~4d 17h 30m 66 11/24/97 13:30 ~3d 18h 67 11/30/97 11:00 ~5d 21h 30m 68 12/03/97 23:45 ~3d 12h 45m 69 12/08 97 03:30 ~4d 03h 45m 70 12/12/97 06:30 ~4d 03h 71 12/16/97 08:01 ~4d 01h 31m 72 12/20/97 06:02 3d 22h 01m 73 12/24/97 15:56 4d 09h 54m 74 12/29/97 17:43 5d 01h 47m 75 01/02/98 20:14 4d 02h 31m 76 01/06/98 11:51 3d 15h 37m 77 01/10/98 11:58 4d 00h 07m 78 01/14/98 09:05 3d 21h 07m 79 01/17/98 19:51 3d 10h 46m 80 01/21/98 12:16 3d 16h 25m 81 01/25/98 13:30 4d 01h 14m 82 01/29/98 06:38 3d 17h 08m 83 02/02/98 03:58 3d 21h 20m 84 02/06/98 00:23 3d 20h 25m 85 02/10/98 06:06 4d 05h 43m 86 02/14/98 13:34 4d 07h 28m 87 02/18/98 23:30 4d 09h 56m 88 02/22/98 08:02 3d 08h 32m 89 02/26/98 10:00 4d 01h 58m 90 03/02/98 14:48 4d 04h 48m 91 03/07/98 05:58 4d 15h 10m 92 03/12/98 13:37 5d 07h 39m 93 03/17/98 16:19 5d 02h 42m 94 03/23/98 16:15 5d 23h 56m 95 04/13-14/98 ------- ~21d 07h Between 23:00 4/13 and 01:00 4/14 96 04/30/98 ------- ~16d 04h Estimated time of 04:00 97 10/15/98 08:23 ie ~168d 03h Observed in eruption 98 05/09/99 07:27 ~205d 23h 99 06/20/99 00:40 ~41d 17h Observed late in eruption 100 07/29/99 05:30 ie ~39d 05h Observed in eruption 101 11/02/99 06:15 ~96d 02h 102 11/08/99 01:34 5d 19h 20m 103 11/28/99 15:29 20d 14h 55m 104 12/09/99 12:58 10d 21h 30m 105 1/7-8/00 ------- ~29½ days Known from observations of platform 106 1/27-28/00 ------- ~20 days Known from observations of platform 107 3/31 –4/01/00 ------ ~64 days Known from observations of platform 108 4/07/00 13:59 ~7 days 109 4/14/00 09:32 6d 19h 33m 110 4/22/00 09:50 8d 00h 18m Occurred at recovery from marathon 111 5/10/00 18:40 vr 18d 08h 50m Occurred during Grotto marathon 112 9/20-21/00 at night ~133½ days Based on platform observations 113 9/27/00 08:13 ns ~7d 06h North function; Grotto i.e. at start 114 10/04/00 14:01 7d 05h 55m North function 115 10/23/00 early am ~18½ days South function, signs under b’walk 116 10/27-28/00 night ~5 days Unexpected; signs to river! 117 11/02/00 19:03 ie ~6d 18h YNP closed, lucky sighting Hougham 118 ? one or more eruptions suspected 119 11/25/00 11:40 ie Seen by Ranger Dimmick, per Keller 120 11/30/00 evening ~5½ days Not seen, time inferred 121 12/07–08/00 midnight ~7 days North function per platform obs 122 12/20/00 07:37 ns ~12d 07h L. Stephens at Grand, dense fog 123 1/02/01 21:02 ie? ~13d 14h “Big steam cloud”; platform washed 124 4/15/01 04:00 est ~102d 08h Not North function per sign logs 125 7/11/01 19:19 ~87d 15h North function (Mastiff 40’ only) 126 8/27/01 11:44 46d 16h 24m South function 127 9/16/01 11:53 ns 20d 00h 09m “Smallish” South function 128 10/7–8/01 night ~21½ days South function, per washed signs 129 10/29/01 14:43 ~21½ days South function (Mastiff 30’ max) 130 in November, date(s) unknown, at least one eruption 131 12/18-19/01 night > 16 days South function 132 01/01/02 1718 ie ~13½ days Eruption characteristics not reported 133 03/8/02 19:23 ~66 days per Jens Day’s electronic monitor 134 03/26/02 15:51 17d 20h 28m South function; electronic time 135 04/02/02 14:17 ie ~6d 22h South function? 136 04/14/02 12:27 ~11d 22h South function? 137 07/12/03 20:55 ns ~454d 08h 28m longest interval since 1986 138 12/24/03 22:01 165d 01h 06m confirmed by recorder; fctn unknown 139 05/30/04 13:21 157d 15h 20m South function 140 07/15/04 12:02 45d 22h 41m South function 141 08/02/04 16:40 18d 04h 38m South function 142 09/26/04 22:35 55d 05h 55m North function 143 10/11/04 15:15 14d 16h 40m North function, height only 170 feet 144 11/24/04 07:32e 43d 17h 17m electronic time only (park closed) 145 12/13/04 14:16e 19d 06h 44m no information–1st seen 30 min into eruption 146 08/06/05 08:50 235d 18h 34m Mastiff 30 feet, replaced by Catfish before 147 08/29/05 11:00 23d 02h 10m South function, Mastiff had dropped 148 09/16/05 09:56 15d 22h 56m Mastiff 35 feet, Catfish 50+ feet 149 09/29/05 07:40 12d 21h 44m South function 150 10/11/05 05:20est ~11d 21h 40m estimated time, seen late in eruption Times from 11/2/2005 through 5/6/2006 from Jens Day’s recorder 151 11/02/05 14:35 22d 09h 15m estimated time, seen early in eruption 152 11/09/05 16:05 7d 01h 30m based on washed signs, C. Loren 153 11/24/05 14:30 14d 22h 25m seen i.e. by Katy Duffy 154 12/01/05 21:55 7d 07h 25m based on platform snowmelt 155 12/16/05 17:40 14d 19h 45m probably North fctn based on snowmelt 156 12/25/05 05:55 8d 12h 15m sign logs washed off of platform 157 01/07/06 18:58 13d 13h 03m North function; Keller observation 158 01/15/06 13:15 7d 18h 17m probably South function, rather weak 159 01/26/06 16:30 11d 03h 15m seen late i.e., bursts ~40 feet high only 160 02/03/06 09:11 7d 16h 41m seen i.e. Doug Holstein, perhaps weak 161 02/14/06 00:36 10d 15h 25m sign logs washed next day; snow @2200 162 02/26/06 04:46 12d 04h 10m sign logs found washed morning 2/26 163 03/08/06 18:40 10d 13h 54m steam cloud time; sign wash minimal 164 03/15/06 03:41 6d 09h 01m known from electronic record only 165 03/24/06 01:41 8d 22h 00m known from electronic record only 166 04/2-6/06 ----- ~13 days sign logs found washed on 4/8, 4/6 likely 167 04/10/06 14:16 ~4 days known from electronic record only 168 04/13/06 18:21 3d 04h 05m seen in eruption by Xanterra employees 169 04/16/06 11:31 2d 17h 10m washed signs confirmed by electronics 170 04/20/06 02:21 3d 14h 50m washed signs confirmed by electronics 171 04/23/06 11:33 3d 09h 12m very odd hot periods, seen by many 172 04/26/06 21:36 3d 10h 03m washed signs confirmed by electronics 173 04/30/06 22:10 4d 00h 34m observed after dark by D. Goldberg, et al. 174 05/6/06 22:20 6d 00h 10m North function; 8 gazers present 175 05/14/0608:04 7d 09h 44m North function 176 05/21/06est 01:00 ~ 6d 17h known from washed sign logs only 177 05/31/06 07:15 ~10d 06h seen by Mike Frazier, no details reported 178 06/06/06 17:27 6d 10h 12m North fctn, but Mastiff off before Giant start 179 06/17/06 19:20 11d 01h 53m South function between normal Grottos 180 07/03/06 19:25 16d 00h 05m South function 181 07/13/06 08:35 9d 13h 10m South function, out of Feather restart 182 07/23/06 13:20 10d 04h 45m Full Mastiff with Catfish (true Mastiff fctn?) 183 07/30/06 02:39 6d 13h 19m North function 184 08/05/06 15:41 6d 13h 02m North function 185 08/19/06 01:21 13d 09h 40m South function 186 08/27/06 11:43 8d 10h 22m South function 187 09/04/06 13:25 8d 01h 42m South function 188 09/09/06 12:42 4d 23h 17m North function, recovery hot period 189 09/15/06 14:10 6d 01h 28m North function, recovery hot period 190 09/22/06 10:06 6d 19h 56m North function, recovery hot period 191 09/27/06 22:50 5d 12h 44m South function after short Grottos 192 10/04/06 02:56 6d 04h 06m South function with Feather restart 193 10/08/06 13:41 4d 10h 41m South function with Feather restart 194 10/15/06 13:29 6d 23h 48m North function in strong wind (180’) 195 10/22/06 15:44 7d 02h 15m South function 196 10/27/06 18:34 5d 02h 50m Function uncertain, probably Normal Times from 11/6/2006 through 2/12/2007 from Jens Day’s recorder 197 11/06/06 19:35 10d 01h 01m Park closed, rolled sign logs on 11/7 198 11/14/06 04:40 7d 09h 05m Rolled sign logs 199 11/19/06 16:10 5d 11h 30m South function; David Goldberg on site 200 11/26/06 17:58 7d 01h 48m North function; D. Goldberg visual 201 12/03/06 08:10 6d 14h 12m Seen i.e. by NPS maintenance 202 12/13/06 05:00 9d 20h 50m Known only from rolled “Danger” sign log 203 12/23/06 19:40 10d 14h 40m Known only from rolled “Danger” sign log 204 01/03/07 02:15 10 d 06h 35m Known only from rolled “Danger” sign log 205 01/11/07 09:50 8d 07h 35m Reported by visitors, apparently early i.e. 206 01/16/07 13:35 5d 03h 45m Seen via Webcam and then confirmed 207 01/23/07 10:30 6d 20h 55m Various non-NPS guide reports + Webcam 208 02/01/07 08:00 8d 21h 30m Webcam followed by on-site observations 209 02/12/07 05:10 11d 21h 10m Electronic download time Times from 2/18/07 to 6/7/07 from Jens Day’s recorder (when no direct observation time). 210 02/18/07 02:32 5d 21h 22m Rolled sign logs 2/18 (Graham Meech) 211 02/22/07 20:57 4d 18h 25m Rolled sign logs 2/23 (Graham Meech) 212 02/27/07 04:42 4d 07h 45m Known only from the electronic record 213 03/04/07 13:32 5d 08h 50m Carolyn Loren on site most of eruption 214 03/13/07 14:31 9d 00h 59m North function (D. Goldberg) 215 03/22/07 08:10 n.s. 8d 17h 39m Eruption time via webcam 216 03/29/07 02:22 6d 18h 12m Known only from the electronic record 217 04/13/07 04:32 15d 02h 10m Signs found washed @08:00 218 04/24/07 15:40 11d 11h 08m Visitors on-site 219 05/01/07 19:11 7d 03h 31m North function on marathon recovery 220 05/09/07 14:13 7d 19h 02m South function, height 200++ feet 221 05/14/07 12:09 4d 21h 56m South function, Scott Carsley start time 222 05/19/07 12:09 5d 00h 00m North function on marathon recovery 223 05/24/07 05:32 4d 17h 23m South function on restart 224 05/31/07 09:39 7d 04h 07m North function on marathon recovery 225 06/07/07 03:33 6d 17h 54m North function on marathon recovery 226 06/13/07 02:16 5d 22h 43m South function, details unknown 227 06/20/07 14:12 7d 11h 56m North function on marathon recovery 228 06/28/07 12:33 7d 22h 21m North function on marathon recovery 229 07/06/07 19:49 8d 07h 16m South function; failed recovery ~8h earlier 230 07/13/07 07:14 6d 11h 25m South function; failed recovery ~10h earlier 231 07/18/07 08:08 5d 00h 54m North function, Grotto 31+h, recovery >15h 232 07/24/07 00:06 5d 15h 58m South function; failed recovery ~16h earlier 233 07/28/07 07:47 4d 07h 41m North function, recovery ~11 hours 234 08/04/07 04:40 6d 20h 53m North function, recovery ~9½ hours 235 08/10/07 05:48 6d 01h 08m South function, on restart 236 08/17/07 12:51 7d 07h 03m South function, failed recovery 5½ hours earlier 237 08/25/07 05:28 7d 16h 37m South function, on restart 238 08/30/07 10:17 5d 04h 49m South function 239 09/08/07 15:32 9d 05h 15m North function 240 09/15/07 21:37 7d 06h 05m North function after mini-marathon 241 09/22-23/07 overnight ~7d 06h Post-marathon so probably North function 242 09/28/07 23:45ns ~5 days North function, Mastiff 2340ie 243 10/05/07 06:45ie ~7d 07h function unknown 244 10/10/07 10:34 ~5d 03h 50m South function 245 10/16/07 13:25 6d 02h 51m North function (Mastiff “huge”) 246 10/22/07 12:20vr 5d 22h 55m South function 247 10/26/07 23:47 4d 11h 27m North function; Mountain Daylight Time 248 11/01/07 08:25 5d 08h 38m South function; Mountain Standard Time 249 11/06/07 17:04 5d 09h 39m probably North function (wc); Standard Time 250 11/12/07 09:34 ns ~5d 16h 30m webcam observation 251 11/18/07 12:00 ie ~6d 2½h probable, per webcam 252 11/25/07 01:51ns ~6d 14h webcam under full moon 253 12/3-7/07 nothing known; marker replaced 12/7 afternoon 254 12/10/07 16:30ie webcam observation 255 ? ? ? 12/20 sign perpendicular to normal position 256 12/21/0713:15 vr prob 5½d x2 vr is near start, reported to VC on cell phone 257 12/30/0708:43 ~8d 19h 28m Kitt Barger on site, N function 258 01/14/08 ~8d X 2 double int we hope; marker logs found washed 259 01/21-22/08 overnight ~7½ days reported by Xanterra employee; confirmed 260 01/26-27/08 ~5 days marker logs washed and in solid ice on 1/29 261 02/04/08 07:00 ns 9 days or so Webcam steam confirmed 262 02/09/08 22:05 5d 15h 05m marker logs found washed 263 02/19/08 09:32 9d 11h 27m North function; Meech and Loren on site 264 02/27/08 15:33 ns 8d 06h 01m North function, per French tour guide 265 03/04/08 04:15 5d 12h 42m marker logs found washed; Standard Time 266 03/11/08 18:30 7d 13h 14m Webcam steam observation; Daylight Time 267 03/22/08 22:10 11d 03h 40m marker after 3/11, in place 3/22, replaced 3/26 268 03/28/08 17:51ie 5d 19h 41m Webcam observation 269 04/04/08 22:45 7d 05h 54m marker logs replaced 4/4/08 270 04/16/08 10:39 ns 11d 16h 48m Webcam observation 271 04/29/08 15:02 13d 4h 23m South function, possibly on Feather restart 272 08/26/08 07:04 ns 118d 16h 02m South function; brief hot period at best 273 10/3/08 00:54 37d 17h 50m time per Jens Day’s monitor 274 02/8-9/09 unk prob in night if at all – signs only slightly moved 275 01/15/10 20:56 340d 19h 56m signs moved; logger confirmed 276 01/22/10 00:56 6d 04h 00m logger record only Giant Geyser, eruptive activity since 1955 — compiled by T. Scott Bryan, 06/02/2008