. The geography of New Zealand. Historical, physical, political, and commercial . rs two of these, Virginia and West-mere, provided the source of water supply forWanganui, a town of 6,000 inhabitants. (6.) Near Auckland the miniature volcanoes havesent forth many lava streams. These soon flowedinto the stream channels and blocked them up. Inone of these Lake St. John was formed by thedammed-up waters. In the same way the lavas fromTongariro blocked up a stream between that volcanoand Pihanga. Thus was Lake Rotoaira formed. (c.) In river beds where the main stream hasreached its base level of e
. The geography of New Zealand. Historical, physical, political, and commercial . rs two of these, Virginia and West-mere, provided the source of water supply forWanganui, a town of 6,000 inhabitants. (6.) Near Auckland the miniature volcanoes havesent forth many lava streams. These soon flowedinto the stream channels and blocked them up. Inone of these Lake St. John was formed by thedammed-up waters. In the same way the lavas fromTongariro blocked up a stream between that volcanoand Pihanga. Thus was Lake Rotoaira formed. (c.) In river beds where the main stream hasreached its base level of erosion and the rate ofdeposition equals that of removal of material, an LAKES 185 active tributary may block the stream it joins, anda lake will then form in the main stream behind thebarrier. The main stream in other cases blocks upsome of its tributaries in the same way and lakesare formed in the valleys. Sometimes, a stream witha meandering course may cut through the narrowneck of the meander and the old curved channel isat tirst an anabranch taking but little of the water;. Crater lake of IMouut Kuapchu. before long its connections with the main streamare blocked up by mud, and a curved lake lakes in the Waikato valley (see map, p. 1-42)occupy the valleys of tributaries and in theWaihola River near the gorge an anabranch has beenformed, but the ends are not yet silted up, and thereis a similar instance in the Waitotara River. (d) The mighty glaciers that long ago filled themountain valleys have left many traces of theirformer presence. Their large terminal moraines have 186 GEOGRAPHY OF NEW ZEALAND blocked up the valleys of many mountain rivers ands(mie of onr largest lakes now occupy the valleys inwhich the ice flowed; for example, Lakes Coleridge,Pukaki, Tekapo and to some extent Manapouri andTe Anau, though it is probable that the two lasthave their floor far below the base of the morainicaccumulations that are found alongside of lakes in almost
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