Lake Disappear lies in a valley dammed by a lava flow and drained through a limestone sinkhole. The lava flow, which covered the limestone, was part of the Okete Volcanics about 2 million years ago, coming from a vent on Whataipu, just over a kilometre away. Page 43 of the 'Geology of the Raglan-Kawhia Area' says, “Only a few specific areas within the larger catchments are prone to flooding where river flow is restricted, most notably at Lake Disappear Here, the Pakoka River drains underground through limestone. During times of prolonged heavy rain, water backs up behind the outlet to form a sizable lake over what are normally dry alluvial flats.” Elgood Limestone is part of the Glen Massey Formation. The geology guide describes it as, “forming prominent bluffs or surface outcrops displaying solution channels, lapiez, and sinkholes, and is everywhere a light grey, flaggy limestone containing up to 95% CaCO3. Glauconite is common throughout, together with Mesozoic pebbles and greensand near the base”. About its late Whaingaroan creation, it says, “The change from estuarine, shallow brackish water conditions, to fully marine, open sea, aerobic conditions is evidenced by near shore accumulation of the bioclastic Elgood Limestone, onlap of the succeeding Dunphail Siltstone, and subsequent deposition of Ahirau Sandstone in an inner to mid shelf environment.”
Biota
Pakihi is a Māori term now commonly used to describe poorly drained, infertile land. Much of the watershed of Lake Disappear was podocarp forest but is now mostly sheep and beef farms, with Te Uku Wind Farm around the source. A 1999 survey reported the lake-bed as dominated by adventive pasture species, with some indigenous sedges, and a remnant of secondary kahikatea forest. A survey for the windfarm described the Pakihi, 2 km up from the Lake, as having poor to moderate ecological health, indicated by significant growths of long-green filamentous algae. Landcare Research says, “Enrichment of the water with nutrients causes algal blooms, and changes the algal community from a slowgrowing, diverse mixture into one dominated by problem algae like thick filamentous mats”. Inanga, longfin eel, koura, freshwater snails, shrimps and banded kokopu have been found in the stream and Kaoro Climbing galaxias may be present. A January 2008 survey identified these indicators of stream quality as being present - Caddisfly Olinga feredayi spiny-gilled mayfly Coloburiscus humeralis occasional mayfly Deleatidium occasional double-gilled mayfly Zephlebia occasional caddisfly Rhyacophilidae abundant dobsonfly Archichauliodes diversus common riffle beetle Elmidae 6 occasional stony-cased caddisfly Pycnocentrodes common Crustacea Paratya curvirostris occasional mud snail Potamopyrgus antipodarum common sand flyAustrosimulium occasional New Zealand freshwater mussel Hyridella rare
