Reserve Created To Preserve Terraces

Press, Volume CIII, Issue 30498, 21 July 1964, Page 19

Reserve Created To Preserve Terraces

The first private historic reserve to preserve a geological feature has been gazetted. It comprises 626 acres on the property of Mr H. S. F. Houghton, in the Wairau valley, 40 miles west of Blenheim, and is to ensure the preservation of a series of terraces formed by the Branch river, a tributary of the Wairau, that have been offset by faulting. According to the secretary of the Geological Society of New Zealand (Mr D. R. Gregg), river terraces displaced by recent faults are, as far as is known, unique to New Zealand.

“These terraces, displaced both vertically and horizontally by repeated movements on the faults, enable the rate of downcutting of the rivers —the process that forms terraces—to be related to the rate of fault movement,” Mr Gregg said. “The higher, and thus older, terraces are displaced by greater amounts than the lower terraces. Studies of such features provide essential information to assess movements on the faults in the past, and to assist in predicting movements. 400-mile Feature

"The great alpine fault is the major structural feature of New Zealand, and stretches for 400 miles through the South Island from Milford Sound to Blenheim. At its northern end it runs along the Wairau valley and has displaced the terraces of the Branch river. Professor H. W. Wellman, of Victoria University, of Wellington, was the first to describe the faulted terraces at the Branch, and also suggested that the part of the South Island on the east side of the alpine fault, including Southland, Otago, Canterbury, and most of Marlborough, has moved 300 miles south along the fault in the last 150 m years. “At the Branch river, a series of seven terraces has been displaced by faulting. The youngest terrace, Bft above the river, has been displaced 33ft horizontally

and 3ft vertically the highest terrace, 44ft above the river has been displaced 195 ft horizontally and 10ft vertically. This has been estimated to give a rate of movement on the fault of Jin a year horizontally, and l/16in a century vertically. Professor J. B. Mackie, of the University of Otago, has installed survey markers on either side of the fault to measure this movement.

“The Geological Society considered it highly desirable that some examples of these faulted river terraces be preserved not only as a record of movements that have accompanied earthquakes, but also as reference marks against which to measure future displacements. The society desired the terraces to be protected from earthmoving and cultivation, and opened negotiations with the New Zealand Historic Places Trust in 1962, and subsequently with the Nature Conservation Council.

“Mr Houghton has co-opera-ted generously with the society, and the agreement to set up the reserve was signed in June. Mr A. C. Coull, of Blenheim, and Professor Mackie acted for the society.” The agreement specifies that the owner will maintain and preserve the character of the land in its existing condition. No ploughing, digging, excavating, or other disturbance of the soil may be undertaken without the consent of the Minister of Lands.