WATER'S RISE AND FALL

New Zealand Herald, Volume LXX, Issue 21423, 22 February 1933, Page 11

WATER'S RISE AND FALL

LAKE TAUPO MOVEMENT FLUCTUATION DUE TO SEICHE NOT UNCOMMON OCCURRENCE The Herald's Rotorua correspondent states that a remarkable incident occurred recently at Lake Taupo. While working on the *oad at about 10 a.m. some relief workers who are building a retaining wall i near the wharf at Taupo, suddenly found themselves nearly surrounded by water to a depth of a few inches. On investigation they found that the lake in this vicinity had risen approximately 12in., the rise taking about 13 minutes. The water then started to recede to normal, and this took nine minutes. The water remained steady for about four minutes, when it commenced rising again, and this pulsation was continued at regular intervals until the week-end. The conditions then became normal, the pulsations having ceased in the vicinity of the landing reserve. The pulsation also affected the Waikato River in the Taupo district for about three-quarters of a mile, although the rise and fall was not quite so pronounced. Fishing was in no way affected and some anglers enjoyed good sport. The movement in the lake level is explained by Mr. Ralph H. Ward, of Taupo, who writes:—"Movement is apparently of the type of fluctuation first observed at Lake Geneva and known as a seiche. Such movements of lake level are not uncommon at Taupo. They were observed there by the writer in 1922, in various parts of the lake, notably in Tapuaeharuru Bay, near the Waikato River outlet, at Acacia Bay and at Whakaipo Bay. The movement observed consisted on one occasion of a rise in the lake level of as much as 6in., occupying 20 minutes, followed after about four minutes by a fall to the original level, occupying 20 minutes, the f>henomenon being repeated for the hour and a-half during which observation was maintained. Other seiches observed produced fluctuations of smaller degree and occupying shorter periods. The late Rev. H. J. Fletcher, who was stationed for 30 years at Taupo, informed the writer that he had also observed the phenomenon on various occasions. "Similar fluctuations of level are known to occur in other lakes in the district, notably at Lake Tarawera. They were specially noticeable there for several years following the Tarawera eruption of 1886. Seiches are probably due to several factors acting together or separately, such as sudden variation of atmospheric pressure, and changes in strength or direction of wind. Explanations such as lunar attraction or earthquakes have been shown to bo untenable as general causes of soiches. "In such ( cases as the Tarawera Lake seiches, however, the proximity to a recently-active volcanic vent raises the presumption of a possible cause in earth movements in the vicinity of the lake. The maximum height of a recorded seiche at Lake Geneva is rather over 6ft. Study of seiches has shown that the effect of the movement is sometimes four times as great at one end of a lake as at the other. The reports of the Taupo occur•rence do not indicate any features of a hitherto unknown nature, and do not give cause for alarm." Ihe matter was also referred to Dr. G. E. Adams, Dominion seismologist, and Dr. E. Kidson, Government meteorologist, in Wellington. Both considered that the movement of the water was due to seiches.