
Activity Recorded by Data Logger  by Ralph Taylor 



Introduction 
Grand Geyser has been monitored using electronic data loggers since 1999. The record is not complete for these years but there is a substantially complete record from 2002 to the fall of 2008 with only a few gaps.
A gap from 20 to 31 January 2008 resulted from a sensor failure. A gap from 1954 on 24 May to 1054 on 27 May due to memory filling.
The Grand logger failed after the 6 November download. Some data from a second logger are available after 6 November 2008 but there are numerous gaps.



Activity in 2011 
The overall statistics for 2011 are shown at Grand 2011 Statistics. A pdf of this summary is at Grand Geyser Recent Activity Summary.




The activity of Grand Geyser in 2011 is shown in the graph at the right. The blue line shows all of the eruption intervals and the yellow line shows the 1week moving median interval. The graphs for the current year are updated about every six weeks from October to June and weekly from June to the end of September.

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Grand Geyser's activity for the recent past is shown in the next graph, and the activity for the past month in the third graph below.

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The current year graph shows longer term trends while the other two shorter timeline graphs give a better sense of the most recent activity.

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Another useful representation of a geyser’s activity is the distribution of intervals. The next chart shows the distribution of intervals for the whole of 2011 to date, the most recent month of data, and the most recent week of data. This chart illustrates the range of intervals that necessitates the four hour prediction window. Note that in this and the other histograms displayed here the labels shown on the Xaxis represent the upper boundary of the class, not the midpoint. Geyser times are traditionally truncated. The graph at the right has class widths of 15 minutes. The bar appearing above the label "8:15," for example, contains intervals from 8h01m through 8h15m.

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The monthly statistics graph shows the maximum, mean, median, and minimum intervals for each month. This chart summarizes the range and gives another perspective on the activity. The minimum value is an indication of how soon after the previous eruption one must arrive at Grand to be (relatively) sure to see the next eruption and the difference between the minimum and maximum suggests how long the wait could be.

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Another slant on this is shown in the prediction graph which shows how the current prediction would have fared as applied over the past week and month. This graph shows the percent of all intervals that fall below the prediction window, in each quarter of the window, and the percentage of intervals that are longer than the window.

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Activity since June 1999 
One way to present the eruption interval data is to graph the interval as a function of time. The graph shown at the right shows all of the electronically recorded intervals since 1999. The gaps in 1999, 2000, and 2001 are many weeks long and resulted from the logger filling during times that the Park is closed. We were somewhat more successful since then, but in the winter of 20045 there were technical problems with the logger.

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The interval graph shows the large variation in interval from one eruption to the next. A better idea of the change in intervals over time can be seen from the graph of the 1week moving median intervals, shown at the right. Grand has experienced a decrease in intervals over the time shown. In 1999, 2000, 2001, and 2002 there were brief (2 to 3 week) periods of short intervals, more clearly shown on the moving median graph than on the interval graph, but in all of these cases Grand soon reverted to its longterm behavior. However, following the several week short (about 7 hour) interval series in mid2002 although Grand reverted to 11 hour intervals in August a gradual and steady decline in intervals began which continued until March 2003, then another decline started in late 2003 that continued until Grand’s weekly moving median dropped below 7 hours in August 2004. Moving median intervals have remained in the 78 hour range since with little change.

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The graph at the right shows Grand's interval statistics on a month by month basis, including the maximum, minimum, mean, and median intervals for each month. Note that before 2005 the mean interval was roughly halfway between the minimum and maximum for each month, but since early 2005 the mean has been closer to the minimum. This was because most intervals were short and there were few intervals near the maximum.

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Activity in 2010

Activity in 2009

Activity in 2008

Activity in 2007

Activity in 2006

Activity in 2005
