Submitted by admin on April 22, 2009 - 22:45
BAY OF ISLANDS VOLCANOES
Between the Bay of Islands and the upper reaches of Hokianga Harbour is to be found evidence of numerous volcanic cones and lava flows, some more eroded than others, and hot springs, often a sign of quiescent volcanic activity. No less than 26 known centres of eruption have broken through and spread over the older basement rocks in an area southward from Matauri Bay to Taheke and eastward from Horeke to Paihia. Lava flows have partly filled valleys (Moerewa) and formed waterfalls (Kerikeri Bridge), lakes (Omapere), and swamps (Punakitere). The volcanic material is principally basalt, although much older andesites form the rugged outcrops, including St. Peter and St. Paul, near Whangaroa, to the north. A few small rhyolitic domes, like Putahi, are present. Near Pungaere are blocks of black volcanic glass called obsidian, which is not found on the neighbouring rhyolitic domes. The basalts can be divided into two groups, according to age, by sequence and degree of erosion. The older group (Horeke Basalts) includes among others, Te Whau, Tipene, and Otoroa, and is extensively eroded in many places to small isolated outcrops. Some of these deeply weathered lava sheets near Takou Bay have been prospected as a possible source of bauxite for an aluminium industry. Tauanui, Te Puke, Kawiti, and Te Ahuahu belong to the younger group (Taheke Basalts) that still retain their distinctive conical forms and well-formed craters. Their activity has continued into the last 2,000 years, although not recently enough to be recorded in Maori folk lore. The lava flow originating from Tauanui has travelled 15 miles down Punakitere Valley toward Hokianga Harbour. Abundant unweathered surface rocks are collected and used for stone fences. In pre-European times Maori warriors excavated the steep-sided, easily worked hills to great advantage as pa sites. Today the scoria and basalt are quarried for road materials.
by Leslie Owen Kermode, B.A., Geological Survey Station, Department of Scientific and Industrial Research, Otahuhu.