Submitted by admin on April 23, 2009 - 00:23
The Chatham Rise is an elongated submarine platform running eastward from the neighbourhood of Banks Peninsula, and extending over 100 miles beyond the Chatham Islands. The crest of the Rise lies mainly at depths between 100 and 300 fathoms, but it rises to 28 fathoms at the highest point of the Mernoo Bank (near the western end of the Rise) and breaks surface at the Chatham Islands. The width of the Rise, measured at the 500-fathom isobath, ranges from 75 miles in the centre of the Rise to 115 miles at the Chathams and 130 miles opposite Mernoo Bank.
Near its western end, the northern slope of the Rise abuts against the Hikurangi Trench, but further east the Rise descends more gradually to the floor of the South-west Pacific Basin. On the south side, the Rise descends and passes into the Bounty Trough.
About 60 miles south of the main crest of the Rise, there occurs the Veryan Bank, an ancient truncated volcano which rises to a minimum depth of 80 fathoms. Most of the surface of the Rise is covered with globigerina ooze – a sediment made up of tiny shells of foraminifera. In places this is mixed with greenish glauconite and in some areas there occur blocks of older Tertiary ooze which have converted to a hard limestone and subsequently phosphatised.
by Henry Moir Pantin, B.A.(CANTAB.), PH.D.(CANTAB.), New Zealand Oceanographic Institute, Department of Scientific and Industrial Research, Wellington.