NATURAL HISTORY OF GEYSERS AND OTHER THERMAL SPRINGS.
In Icelandic speech the word _geyser_ means simply _rager_, and is applied indiscriminately to all turbulent fountains of water or mud. The most violent and noisy "rager" on the island being the great intermittent spouting spring near Haukadal, it naturally gained for itself the title, The Geyser; and being the earliest known and most remarkable fountain of the kind, its native common name was adopted in other languages as the generic name for all springs of its class.
The history of this great, but no longer the greatest geyser, begins in the early part of the fifteenth century, when its eruptions are mentioned in Icelandic records. In the middle of the seventeenth century the Bishop of Skalholt noticed its daily discharges. A hundred years later Olafsen and Povelsen described it as having three or four eruptions a day, some of them attaining the height of 300 feet, including, doubtless, the uprush of vapor. The depth of its tube was then 72 feet; now it is commonly given as 74, though Commander Forbes, R. N., claims that it is not so deep by ten feet. In 1774 Von Troil estimated the height of the ejected column at 92 feet. Seventeen years later, Stanley gave 96 feet as its greatest height. Forty yards west of the Geyser this traveller found a rival, called the Strokr, (in English, the Churn,) playing to the height of 130 feet. The same year, 1789, an earthquake destroyed the mechanism of the Strokr, converting it into a quiet reservoir of boiling water, whereupon its name was transferred to the present Strokr, which then became especially active and noisy. In 1804 the Geyser had regained somewhat of its ancient power, erupting every six hours to the height of 200 feet; and the original Strokr had repaired its tube so that it could lift a column to nearly the same height and sustain it for a much longer period. During the next five years the power of the Geyser fell off a half, and its paroxysms became much less frequent--Hooker estimating its column, in 1809, at 100 feet, and Mackenzie, a year later, at 90 feet, its eruptions taking place every thirty hours. At the same time the Strokr played every ten or twelve hours, sixty feet high, for the space of thirty minutes. In 1815 the periods had changed again, the Geyser erupting every six hours, to an average height of 80 feet,--the jets occasionally reaching 150 feet, while the Strokr had prolonged its quiet intervals to twenty-four hours. Of late years the Geyser's violent eruptions seldom occur oftener than once in thirty hours, and do not exceed 100 feet in altitude, and generally averaging 70 or 80 feet. Between these eruptions are usually two minor spirts, attaining from 30 to 50 feet. The Strokr is exceedingly irregular in its operation, and generally requires a dose of turf to bring on an exhibition.