DJ Lowe and J D Green

Reference: Lowe, D.J.; Green, J.D. 1992. Lakes. Pp.107-143 in J.M. Soons; M.J. Selby (eas) Landforms of New Zealand Second Edition. Longrnan Paul, Auckland.

INTRODUCTION 'destructive' when the basin is excavated, and 'obstructive' when a pre-existing valley or Lakes have always held an aesthetic fascination depression is dammed (Hutchinson, 1957). A for people; they figure prominently in both art and variety of geological processes can act in these literature and have even been endowed with ways to form lake basins- eg, tectonism, spiritual qualities. For example, the nineteenth volcanism, glaciation, wind and river action, and century American writer Henry D. Thoreau (1854) landslides-each producing a distinctive type of considered a lake to be 'the landscape's most lake. In New Zealand, the great variety of beautiful and expressive feature. It is the earth's geological processes (chapter I) has resulted in a eye; looking into which the beholder measures the corresponding wide array of lake types. Thus, depth of his own nature'. More prosaically, lakes New Zealand perhaps has a greater variety oflake are also of considerable geomorphological interest types in a small area than any other country. as dynamic landfonns originating in varied and often complex ways. A lake can be defined generally as a body of standing water occupying a basin and lacking CLASSIFICATION AND continuity with the sea (Forel, 1892), and forms DISTRIBUTION when a process, or processes, produce a depression surrounded on all sides by a rim higher than the Various classifications of lake origins have been deepest enclosed point. The processes involved are suggested, the most comprehensive being that of 'constructive' when the rim is actively built, Hutchinson (1957) who defined 76 modes of origin based on the final geological process that allows the basin to hold water. This is essentially Table 5.1 Classification of New Zealand lakes based on mode of foonotion. After Lowe and Green (19870). the approach that has been adopted to classify New Zealand lakes (eg, Irwin, 1975a, b; Lowe lAJ;,ctypt Mode ojjomUJ.tiorl and Green, 1987a), although these classifications Gl,ci,l (G) Glacial activity utilise fewer, deliberately generalised categories Volcanic (V) Volcanic activity because many New Zealand lakes have originated Dun, (D) Wind action by a combination of processes. The categories do Rivenne (R) River action correspond broadly to the major divisions of L.ndsl;d, (L) . Landsliding Barrier·bar (B) Current or wave action on shorelines Hutchinson's classification, however. The classifi Tectonic (T) Faulting or folding cation adopted by Lowe and Green (l987a) is Solution (S) Dissolulion of carbonate rocks shown in Table 5.1. P'" (P) In peat or by peat accumulation New Zealand lakes are grouped into rather Human activity Artificial (A) distinct lake districts because of the dominance of 108 Landforms of New Zealand

N N t t NORTH ISLAND SOUTH ISLAND

F¥!.CIFIC OCEAN

TASMANSEA

PACIFIC OCENI/

o 100 200 km o 100 200 km ~'-'~~ L.'__ ''- _-1'

Figure 5.1 The generalised grouping of lakes in New Zealand into districts reflecting the predominance of particular goologi=1processes, 01. Northland-Auckland-Waikato dune lakes; 02. Mangawhai dune lakes; Sl. Waitomo solution lakes; 03. Wanganui-Manawatu dune lakes; 04. Gisbome dune lakes; 05. Sou1hland dune lakes; Vl. Rotorua-Taupo volcanic lakes; V2. Northland volcanic lakes; Rl. Kaihu riverine lakes; R2. Waikato riverine lakes; R3. Bay of Plenty riverine lakes; R4. Hawke's Bay riverine lakes; R5. Manawatu riverine lakes; R6. Ruamahanga riverine lakes; R7. Wairau riverine lakes; R8. Tairei rlverine lakes; R9. Balclutha riverine lakes; R10. Mataura riverine lakes; G1. Alps' glacial lakes; G2, Tasman glacial lakes; G3. Westland glacial and river-modified glacial lakes; Al. Auckland reservoirs and vol=nic lakes; A2. Waikato hydrodam lakes; A3. Manawatu reservoirs; A4 and AS. Westland reservoirs; A6. Waitaki hydrodam lakes; A7. CIu1ha hydrodam lakes; Bl. Hawke Bay banier lakes; B2. Paliiser Bay bonier lakes; B3. O'Urville barrier lakes; B4, Christchurch banier lakes; B5, Timaru banier lakes; Ll. Wairoa landslide lakes; L2. Wanganui landslide lakes; L3. Karamea landslide lakes, After Green and Lowe (1987), •

particular geological processes In certain areas the flood plains of the major rivers; 'landslide (Figure 5.1). Thus, 'glacial lakes' are found only lakes' are usually associated with hilly or moun in the South Island, and 'volcanic lakes' occur tainous terrain, particularly in regions subject to only in the North Island, particularly in the earthquakes; 'solution lakes' occur m areas Central Volcanic Region; wind-formed 'dune composed of carbonate rocks (limestone and lakes' arc most common along the west coast of marble); and 'barrier-bar' lakes are developed the North Island; 'riverine lakes' are clustered on along coastal and lake shorelines. Lakes 109

2 Excluding offshore islands, New Zealand has a approximately 3400 km , representing about 1.3% total of about 775 lakes with lengths of 0.5 km or of the land area. The total area of North Island more (476 in the South Island and 299 in the lakes is about 1200 km2 (1 % of the land area) and - North Island; Table 5.2). Glacial lakes are the South Island lakes total about 2200 km2 (1.5% of most common (38%), followed by riverine lakes the land area). (16%), dune lakes (15%), and artificial lakes (8%), The bathymetry (bottom contours) of New which together comprise 77% of all lake types. Zealand's major lakes is well known as a result of The rest include landslide (5%), volcanic (4%), surveys carried out mainly by the New Zealand barrier-bar (4%), tectonic, peat, and solution Oceanographic Institute and published since 1967 lakes « 1 % each), and lakes of uncertain origin as the New Zealand Lake Chart Series or Miscellaneous (9%). In the South Island, glacial and riverine Series. Bathymetric maps are available for at least lakes predominate. Glacial lakes are mostly at 124 lakes, most listed by Thompson (1989). high altitudes (> 600 m asl; Irwin, 1975a; Lowe and Green, 1987a) and most are small. In the North Island, dune and riverine lakes are the most common types, occurring at low altitudes AGES « 90 m). Most of the volcanic lakes of the Central Volcanic Plateau are at higher elevations Lakes are transitory features of the landscape. (> 275 m) and, on the average, are larger than After their initial formation they are eventually other North Island lake types. infilled by sediments and so few lakes world wide are older than about I million years. Most are much younger, having been formed in the late Pleistocene or Holocene, and this is true of New MORPHOMETRY AND BATHYMETRY Zealand where the landscape is youthful and still actively developing (see chapter 2). Most of the Size-related measurements (morphometry), lakes are thus very young in geological terms, including area, depth, length, width, and mean commonly being between 5000 and 10 000 years depth, for 163 New Zealand lakes are summarised old. Details of lake ages are discussed in the by Lowe and Green (1987b). Irwin (1975a, b) and following sections. Livingstone et al (1986) also list useful data, with Livingstone et al (1986) also giving information on catchment characteristics. Table 5.2 Frequency of lake types in New Zealand. Only '. New Zealand's largest lakes are listed in Table lakes with lengths 0.5 km or more are included. After Lowe 2 - '5.3. The largest is Lake Taupo (623 km ) in the and Green (1987a) . central North Island, but the next eight occur in 2 Type North Island South Island Total the South Island (Lake Te Anau, 347 km , is 2 second; and Lake Wakatipu, 289 km , third). Number % NU"1ber % Number % Thirteen of the 20 largest lakes occur in the South Glacial 0 0 289 60 289 38 Island. The deepest lakes are all glacial, and Volcanic 30 10 0 0 30 4 include Lakes Hauroko (462 m), Manapouri Dune 106 35 13 3 119 15 Riverine 67 (444 m), Te Anau (417 m), Hawea (384 m), and 22 54 11 121 16 Landslide 18 6 22 5 40 5 Wakatipu (380 m). Lakes Hauroko and Barrier-bar 14 5 18 4 32 4 Manapouri are the 16th and 22nd deepest lakes in Tectonic 6 2 0 0 6 the world, respectively (cf. Herdendorf, 1984). Solution I

110 Landforms of New Zealand

FORMATION AND DEVELOPMENT by the collapse of deposits following melting of large blocks of ice which have been left by The formation and development of New Zealand receding glaciers. lakes were comprehensively reviewed by Lowe and Green (1987a). The following accounts are 3 Combinations of (I) and (2) modified by non based on this review with the addition of new glacial processes (eg, damming by alluvial fans information. or wind-blown dunes). 4 Lakes adjacent to modern glacier ice ('ice margin' or 'pro-glacial lakes' ); these are usually Glacial Lakes temporary, but commonly recur (eg, associated with the Franz Joseph, Lyell, and Douglas Glacial lakes are found exclusively in the South Glaciers; Gage, 1975, 1980). Island because of the extensive glacial action and reworking of resultant debris there during the In New Zealand, the term 'tarn' (a Scandinavian Pleistocene glaciations when large, often coalescing word for a small mountain lake) is frequently used valley glaciers and alpine ice caps covered most of for any small glacial lake. Such rakes may be the Southern Alps (chapter 2; Suggate, 1990). Clrque or kettle lakes, or small lakes in hollows Most of the lake basins have formed by more than produced by glacial corrasion. one mechanism and many have been modified The basins of many New Zealand glacial lakes later by non-glacial processes such as alluvial of all sizes, may primarily be ice-excavated rock aggradation, faulting, landsliding, or coastal depressions in which the water is held by a rock processes (Gage, 1975). Usually these lakes may hp but further deepened by moraine or fluvio still be classified as glacial because they originated glacial outwash dams. Few are likely to be as a direct consequence of glacial activity. Because retai~ed by solid rock alone (eg, Figure 5.2; Gage, 1975). of such typically complex origins, Gage (1975) Lake Wakatipu, for example, with a maximum grouped New Zealand glacial lakes into four depth of 380 m, is held by a rock rim about 305 m generalised types: high capped with about 75 m of till (Bayly and Williams, 1973). However, moraines around the Lakes in ice-excavated rock depressions. These en.ds of some large, ice-gouged lakes may be only comprise two main types. 'Cirque lakes' occupy mInor features and contribute little to their depth amphitheatres formed by ice action (frost riving (eg, Lakes Rotoiti and Rotoroa). Examples of or freeze-thaw action) at the heads of glaciated smaller, essentially rock-impounded lakes include valleys, usually at higher elevations. Although Hawdon and Letitia (Gage, 1958, 1959). commonly small and comparatively shallow, In the upland areas of northwest Nelson, the some are very deep relative to their surface Southern Alps, and Fiordland, there are many area. 'Piedmont lakes', usually at lower small tarns and some larger lakes lying in the elevations, occupy long, narrow, greatly concave excavated floors of cirques and depressions overdeepened U-shaped valleys produced by (Flgures 5.3 and 5.23). Examples include Lakes large valley glaciers, and include 'fjord lakes' Aorere, Browne, Quill, Shirley, and Unknown. near coastlines. Elsewhere in the world;' the Such lakes are very abundant and hundreds of action of continental ice sheets may produce tarns occur in Fiordland alone. Most of the larger very large lakes (eg, the Great Lakes of North lake~ occupy ?v~rdeepen ed valleys once filled by America), but such lakes are not found in New ?lacler~, and slmllar lakes, probably larger, existed Zealand. In eqUlvalent positions during earlier interglacials 2 Lakes partly or completely enclosed by moraine as shown by the presence of lake sediments in drill or associated fluvioglacial outwash deposits. holes and outcrops. Large glaciers, some more These include the small but abundant 'kettle than 30 km long, excavated the troughs now filled lakes' formed in depressions in moraine ca used by Lakes Hauroko, Monowai, Poteriteri, and Te Lakes 111

Toble 5.3 Some mOfPhometric parameters of the 40 largest lakes by area in New Zeal onc. After Lowe and Green (1987b ).

uwand Typ," Area Maxd,pth Maxlmgth Maxwidth M,an thpth' Max altitu,u§ 'location" (km') (m) (km) (km) (m) (m asl) Arapuni (A2 )' A 14 (28)1 44 7 I nd 110 Avicmorc (A6 ) A 25 (23) 41 18 5 nd 268 Bcnmorc (A6) A 74 (12) 91 26 6 nd 360 Brunner (G I) G 36 (18) 109 (18)* 9 7 51 85 Cokridgc (G I ) G 33 (21) 200 (8) 18 3 99 507 Ellcsmere (B4) B 180 (5) 3 26 13 nd 1.5 Grassmerc (R7) B 13 (29) < I 6 4 nd

Anau m Southland; Hawea, · Ohau, Wakatipu, of Fiordland. It is likely that during the coldest and Wanaka in Otago; Coleridge (Figure 5.4), part of the Last Glacial (Otira) many of these Pukaki, and Tekapo in Canterbury; and Rotoiti fjord valleys contained deep oligotrophic lakes and Rotoroa in ~elson (Figures 20.11, 21.6 and impounded by shallow sills. However, because of 23.6). At the same time, other glaciers gouged out rapidly rising sea levels between about 9500 and the deep, V-shaped valleys now forming the fjords 8000 years ago, sea water over topped the sills and

,I . 112 Landforms of New Zealand

flooded the fjord basins (Pi ekrill et ai. 19901. Lake Lake Johnson Late Pleistocene lill McKerrow is an example of such a fjord lake that has persisted, although it is now tidally-influenced (Pickrill et ai, 1981 ). Mica schist o 500 m These large glacial lakes tend to be steep-sided. ! , ! The bottoms of many of them, including Lakes Scale approx. Manapouri, Te Anau, and Wakatipu, lie below Figure 5.2 Sketch of Lake Johnscn, a glacial lake in an sea level and these zones below sea !cHI are ice-excavated rock basin at 392 m altitude near Lake known as 'cryptodepressions' . The basin floors are Wakatipu. The lake has a maximum depth of abaut 27 m, and the rock rim at the outlet end is about 17 m below generally flat as a result of blanketing lake lake level. After Pari< (1909), and Lowe and Green (1987a), sediment (Figure 5.5), although the original basin surface below the lake sediment may be rather them, both as deltas and basinal fill (Figure 5.6), rugged because of remnants of moraine (eg. Lake Rates of infilling are thus fast compared with most Pukaki; Carter and Carter, 1990). Since th eir other New Zealand lakes. Average sedimentation formation many of the large glacial lakes ha\'e rates in Lakes Tekapo and Pukaki have been been considerably infilled by glacially-derived measured at 10 and 14 mm per year, respectively sediments deposited by the rivers flo wing into (Pi ckrill and Irwin, 1983; Irwin and Pickrill, 1983). Such lakes have acted as giant sediment traps, markedly reducing sediment flow down the Figure 5.3 Lake Quill, a glacial cirque lake at neany Waitaki and Clutha Rivers to the continental shelf 1000 m a ltitude in Fiordland. A smaller, ice·coverec lake in the past 10000 years (Carter and Carter, 1990), lies in another cirque basin about 350 m higher. The Examples of lakes enclosed mainly by moraine Sutherland Falls (580 m high) are visible in the foreground. (D L Homer, DSIR Geology and Geophysics) include Lakes Brunner, Haupiri, Ianthe, -and Mapourika in Westland, and lakes in the Mackenzie Basin, Lake Wahapo, dammed largely by moraines, is currently affected by an active allU\'ial fan of the W aitangitaona River (see Figure 20.7). Lake Mahinapua, near Hokitika, is dammed by ridges of moraine together with sand dunes, while nearby Lake Kaniere lies in a moraine-bound glacial basin modified by a large landslide (Bell and Fraser, 1906). Diamond Lake, to the north of Lake Wakatipu, is dammed mainly by glacial outwash sediments that were probably deposited soon after the retreat of the enlarged 'Wakatipu Glacier' (Figure 5.7) , Some glacial valleys contain small groundwater lakes in enclosed hollows in small areas of ablation moraine or on undulating moraine surfaces (eg, Lakes Alexandra, Blackwater, and Clearwater in Canterbury; Gage, 1958, 1959) . Lake Marymere (Figure 5.8a) is an example of a kettle lake, and occupies an enclosed depression in a old meltwater channel of the former Waimakariri Glacier. Kettle lakes have formed in recent times downstream of the receding Fox Glacier (Gage, 1980). Many lakes throughout the South Island mountains are partly impounded by alluvial fans i I . Rgure 5.4 A winter view of part of Lake Coleridge, a large glacial lake occupying a glacially-carved landscape. r . Alluvial fan deposits can be seen around the shorel ine of the lake; hummocky moraines and small kettle lakes are visible in the foreground. In the background are the Rakaia [left) and Wi lberlorce [right) valleys separated by the Rolleston Range of the Southem Alps. [D L Homer, DSIR Geology and Geophysics) , , Rgure 5.5 Generalised bathymetry [in metres) of Lake Pukaki and profile along line A-B. After Irwin (1972).

! ; I -

~~------r----r~---H------~B 00 vC'J

- ...... ----

A T Summer water level B 0 .. Wintpr water level - I Detta 20- - S - - .c. a. 40- - 0" - - 60- - - - , I , 80 I Om 5 10 15 114 Landforms of New Zealand

or screes, many of which are still active, especially above the tree line (see chapter 6). Earlier ones were formed and reworked by rivers into alluvial fans soon after final rapid deglaciation about 10 000 years ago, often to form or modify lake basins such as Gunn, Hawdon, Heron, Pearson, and Poreua, and Sarah (Figure 5.8a, b). Although Lake Gn!smere may have formed originally behind a moraine loop, it seems to have been greatly reduced in area by the growth of alluvial fans of Cass River and Ribbonwood Creek, with the latter continuing to encroach upon the area of _ L TekaPD the lake into historic times (Figure 5.8b; Gage, 1958, 1959; Harper, 1989). Many of the larger glacial lakes were at much higher levels in the past, as shown by stranded tiers of earlier shorelines marked by cut benches and storm-beach ridges. These earlier lakes were considerably larger in area than at present, but

Figure 5.6 Lakes Ohau. Pukaki. and Tekapo impounded mainly behind terminal moraines. Areas of basinal infilUng and de~aic sediments are also shown. Lake Benmore is a n artificial hydroelectric lake. After Carter and Carter (1990). :.,' .. ',. Delt.aiC fill I-:.- Baslnal fill Glacier ice o 5 10 15 km Figure 5.7 Diamond Lake. north of Lake Wakatipu in ! 1 1 OIago. is a glacial lake dammed against the glacierised Glacial moraine: slopes of Mt Alfred (right) and between glacial outwash /' c.13 - 14 ky BP sediments in the Dart (front) and Rees (back) Valleys. ",-'/ c.8kyBP Stranded high lake· level shorelines flank the Richardson Mountains in the distance (National Publicity Studios. Wellington) c

Lakes 115

I I~ I tN rt.::·, :."1Ablation moraine and ;:: ~ '::". outwash ~ Younger outwash and I ~ pos1-giacial alh..Mum i FIji';1 Former la ke beaches ! I o 1km I Figure 5.B (a) Lake Hawdon, a glacial lake occupying a rock basin and partly dammed by alluvium, and Lake Marymere, a large kettle lake: (b) Lakes Sorah and were probably short lived as a result of down ,. Grasmere, impounded by moraine and alluvial fans, After Gage (1959), cutting at the lake outlets, causing lowered lake L levels (Gage, 1975). For example, Lake Wakatipu I was once much larger and incorporated present day Lakes Hayes and Johnson (Figure 5.9) , Such I· Figure 5.9 Sketch of the enlarged glacial an enlarged lake, with fluctuating levels reflecting I take Wakatipu' compared with present·day Lake glacier advances and retreats, may have persisted ! .' Wakatipu and Lqke Hayes, After.Pari< (1909), and Lowe until soon after about 10000 years ago when I and Green (19810), downcutting of the Mataura outlet exposed the I c. 5 ky BP-present Shotover Delta, thus isolating Lake Hayes (Figure N 5.9), The Mataura outlet was abandoned in favour of the present outlet, the Kawarau River, possibly t around 5000 years ago (Lowe and Green, 1987a; Shotover see also chapter 21), Stranded higher lake-level delta \ LHayes shorelines associated with the enlarged Lake Glacial 'Lake Wakat~u ' Wakatipu are visible in Figure 5,7. Other lakes which have been much larger include Brunner, Hawdon, Hawea, Kaniere, Manapouri, Ohau, Pukaki, Rotoroa, Rototiti, Sarah, Te Anau, and Tekapo, The stranded shorelines around Lakes Tekapo, Pukaki, Ohau, Hawea, Wan aka, and Wakatipu have progressively tilted since their formation because of different rates of tectonic uplift away from the crest of the o 10 km '-'...... _, Southern Alps. Studies on the tilting rates of these shorelines at Lake Tekapo and the other lakes 116 Londforms of New leoland indicate that over a relatively short period, glaciers at the beginning of postglacial environ starting about 10 000 years ago, there was a rapid mental conditions, which can be recognised as retreat of the 'Tekapo Glacier' and a rapid down early as about 15 000 years ago (Suggate, 1990). cutting of the outlet (Wellman, 1979). Sustained retreat of the glaciers was well under Few of the glacial lakes have been dated way by about 13000 years ago and Pillans et al directly, and there have been difficulties in (chapter 2) have suggested that about 12000 attaining a definitive chronology oflate Quaternary years ago is an appropriate age to mark the start glacial deposits (Burrows, 1988; Suggate, 1990). of New Zealand postglacial time. Ice still occupied The dates that have been obtained indicate that sections of many of the valleys, bu t the larger the glacial lakes in their present form all developed glacial lakes must date from near this time and at much the same time, following retreat of the Burrows (1979, 1988) gave a number of radio-

Figure 5.10 Volcanic lakes in the Rotorua area and structural and volcanic features associated with the Rotarua and Haroharo Calderas. The Haroharo Caldera lies within the Okataina Volcanic Centre (marked by the Okataina Ring Structure, ORS). Inset shows Bay of Islands-Kaikohe (1), Auckland (2), and Egmont (3) Volcanic Districts. and locations of Taupo (4), Whakamaru (5), Okataina (6). and Rotorua (7) Calderas within the Taupo Volcanic Zone (TVZ). Based.rnainly an Naim (1989); inset after Cole and Naim (1975), Wilson et of [1984,1986), and Houghton et of (1987).

ROTORUA ROTOMA CALDERA CALDERA N

\ HAROHARO CALDERA HAROHARO \ 7Y.------, VOLCANIC YFault COMPLEX \~ '/ I I \<1>

175°E NORTH ISLAND

. . -- \ L. Okaro O A~~l(a~erewhakaaifu Wellington L. Ngah7wa'" o, 5, 10 km o 100 km L...... J L. Ngapouri 0 " ...... Lakes 117

rr,trb,on dates on lake sediments from Canterbury, main types occur: 'maars', with a surrounding 1"",..."·We:stl:anO, and Fiordland of 10000-12000 years rim built up of material ejected during the The retreat of the glaciers continued rapidly, typically phreatomagmatic eruption, and often interrupted by advances of ever containing water; and others without such a rim extent, and other lakes formed or and which commonly originate by hydrothermal '·"lip,'p modified during the accompanying periods eruptions. 'Volcano craters' may be found near intense erosion and fan building. This phase the summits of raised stratovolcanoes (Bayly until about 9000-10000 years ago and Williams, 1973). forests became established over most of the 3 Blocking of valleys by lava flows or pyroclastic Island (McGlone, 1988; Suggate, 1990). material. many glacial lakes are probably about !!,"JllI1 uOOO-12 000 years old, but others may be older The largest volcanic lakes have been formed by ...~", \pCl""'I" up to about 15000 years) or considerably (I) and (3) acting together and are found within ,younger, depending mainly on location and mode the Rotorua, Haroharo (Okataina), and Taupo of formation. The youngest lakes may be expected Calderas (Figures 5.10 and 5.11). Radiometric : to be found in areas where ice retreat was delayed dating of the pyroclastic deposits (ignimbrites and longest, such as in high altitude cirques or airfall tephra deposits) associated with the . ~ rrasion hollows above about 1000 m. formation of calderas and explosion craters, and contemporaneous lava flows , has enabled the ages Volcanic Lakes of the lakes to be determined in more detail than for most other New Zealand lakes (Lowe and lakes are found in three mam areas, Green, 1987a; Froggatt and Lowe, 1990). with the distribution of recent . volcanism- the Taupo Volcanic Zone, the LAKES IN THE ROTORUA AREA Auckland Volcanic District, and the Bay of Islands-Kaikohe Volcanic District (Figure 5.10, Lake Rotorua (Figure 5.11) occupies the Rotorua , Inset). Volcanic lakes are also found on some of Caldera which was formed about 140 000 years the offshore islands (eg, Mayor Island, Raoul ago following the eruption of the rhyolitic Mamaku Island) and in the Egmont (Taranaki) Volcanic Ignimbrite (Wilson et ai, 1984). A lake formed District. Most of the lakes in their present form soon after and lake levels have fluctuated since are young, although in the Taupo Volcanic Zone (Figure 5.12). The highest level, about 90 m above extensive deposits of diatomite and other lake present lake level, occurred when deposits of the 'sediments show that lakes have always character- Rotoiti Tephra, erupted from the Okataina i - ised the region as it has been low lying for most of Volcano about 50 000 years ago (Froggatt and . .-::- . its recorded history (eg, Grange, 1937; Healy, Lowe, 1990), blocked the northward drainage .. 1975a; Wilson et ai, 1986; see also chapter 11 ). from the lake. This level is marked by extensive In these areas lake basins have been formed by terraces around the lake (see Figure 2.27). The " three major processes which may act in com- lake level remained high until drastically lowered bination (Healy, 1975a): to near its present level about 22 000 years ago when the Rotoiti Tephra deposits were breached, .., ·1 Caldera collapse caused by magma withdrawal and the lake drained northeastwards through the - ~ and faulting following massive eruptions; the valley now partly occupied by Lake Rotoiti. The .. result is usually a large subcircular depression, lake dropped to below its present level between often with precipitous sides. Caldera basins are about 19000 and 9000 years ago. Subsequent ~ usually modified by the extrusion of lava domes. changes in lake depth and area were caused mainly 2' Smaller explosi\'e eruptions, producing craters. by growth of the Haroharo volcanic pile in the ~ . 'Ground craters' extend below the general adjacent Haroharo Caldera in the Okataina ground level and are usually subcircular. Two Volcanic Centre (Healy, 1975a; Kennedy et ai, Figure 5.11 A westward-looking view across part of Lake Okolaina towards Loke Rotorua lying in the Rotorua Caldera. The cliffs adjacent to the narrow arm of Loke Okoloino in the foreground mark the westem margin of the Harohoro Caldera (see Figure 5.10). Lavas ond pyroclastic deposits associoled with the Momaku eruptive episode about 7000 years ago form the shoreline in the immediate foreground; the steep, la rgely bush-covered land beyond comprises myolite domes, lava flows, and pyroclastic deposits erupted mainly in the past c. 250 000 to 140 000 years. (D L Homer. DSIR Geology and Geophysics)

~ ..i ~ • , t i _ Lake wal er level '5 .. ~ .. '0 t&rker bed-sedlmenl ~ q ~ 100 " contact ~vels ,I <'5 ~ ,I ,I eo . --., j • ~• 60 !11 ~ t ~ e i" "~ 40 ~~ ~~ ~ ~.!' ~~ • ~: 23 2 ~ e ~o • • ~o ..~ 20 \t' 6, u ~ \' H Figure 5.12 Variolions in woler levels of Lake Rotoruo 0 from about 50 000 years ogo to the present based on doled tephra marker beds. Present lake level is 280 m 50 40 30 20 G above sea level. Affer Kennedy et a/ (1978), ond Noirn '( e a f S BP ( ~ i 0 DO) and Wood (1987). Lakes 119

1978; ""aim and Wood, 1987). This growth OTt.~)~L~"~.~~~w~er~a~ __-. progressively impeded drainage through the 10 Haroharo Caldera, forming Lakes Rotoiti and 20 f Rotoehu, as described below, until about 7000 g 301\40 ' . years ago the drainage was completely blocked by "", deposits of the Mamaku eruptive episode, and ~60 70 Lake Rotorua was forced to overflow to the north ao into the Okere Channel (Kaituna River) via the 9O.L---====~ western part of Lake Rototiti. Since then lake Rgure 5.13 Generalised bathymetry of (0) Lake levels ha\'e steadily dropped (see Figure 2.23), Tarawera. showing its near-vertical sides and fiat·bottom. probablv because of downcutting at the Ohau and (b) Lake Ngapouri. showing its funnel shope (otter outlet. The higher lake levels between about Irwin. 1968). 7000-4000 years ago may have partly resulted 1l.l4). The 1886 AD eruption of Mt Tarawera from higher rainfall than at present (McGlone, was previously said to have blocked the outlet of 1983), while historical flu ctuations in lake level of the lake (Tarawera River), causing the lake level abou t 1.5 m arc correlated not only with variation to rise about 12 m (Healy, 1975a; Lowe and in rainfall (as in other lakes in the Rotorua area), Green, 1987a). However, R. F. Keam (pers comm, but also with sedimentation in the outlet at Ohau 1987) believes that the outlet was not blocked to Channel (Healy, 1975b) . this extent and that any changes in lake level were Most of the other lakes in the Rotorua area much less (Cole, 1970, implied a rise of < 1.0 m). formed in association with rhyolitic volcanism in Lake Okareka was dammed by lavas associated th e Okataina Volcanic Centre (Healy, 1975a; with the Te Rere eruptive episode (about 2-1 000 ~ aim, 1989 ). Lake Rotoi ti formed after the years ago), Lakes Tikitapu (Blue) and Rotokakahi Rotoma erupti\'e episode about 8500 years ago (Green) were both dammed by lavas of the fin ally blocked drainage from Lake Rotorua. The Rotorua eruptive episode (about 13 000 years ago), western part of the lake occupies the valley and Lake Rotoma, lying in a small collapse .. pre\'iously cut by the outflow from Lake Rotorua, caldera developed much earlier, is dammed by while the deeper eastern end is part of the lavas associated with the Rotoma eruptive episode Haroharo Caldera. Lake Rotoehu occupies a series (about 8500 years ago) (Figure 5.10); Froggatt of \'alleys blocked by lavas of the Rotoma eruptive and Lowe, 1990; Lowe and Green, 1987a; Nairn, episode, and so has a more digitate outline, and is 1989; Nelson, 1983). The basin bathymetry has ~hallower than other volcanic lakes in the area. been modified by the extrusion of other young Lakes Tarawera and Okataina (Figure 5.11) were rhyolite domes near the centre of the lake. The formed chiefly by lava damming and are main part of Lake Rerewhakaaitu originated impounded against the western rim of the much more recently by damming by pyroclastic Haroharo Caldera. As the basins of these comprise flows resulting from the Kaharoa eruptive episode a portion of the caldera, they are deep, steep (about 700 years ago) (Cole, 1970). Awaatua Bay sided, and flat-bottomed (eg, Figure 5.13). on the western shore of the lake is a small explosion Modern Lakes Okataina and Tarawera date from crater about 10000 years old (Nairn, 1989). about 7000 and 5000 years ago, respectively. Smaller, subcircular lakes in the Rotorua area . Okataina may have had a south-draining outlet occupy explosion craters, and generally have I . into the Tarawera valley about 7000-5000 years funnel-shaped basins (eg, Figure 5.1 3). Such lakes ago, and the Tarawera valley was probably include Lakes Rotokawau (see Figure 11.27), . occupied by a small lake, or lakes, before formation Rotongata, and Rotoatua, which are maars of the present-day lake. Lake Tarawera attained formed by basaltic eruptions about 3500 years ago I its present form about 5000 years ago when lavas (Froggatt and Lowe, 1990). They lie at the inter I associated with the Whakatane eruptive episode section of faults. Small crater lakes, originating dammed drainage of the valley to the east (Figure from hydrothermal eruptions, are common and 1 120 Landforms of New Zealand

include Lakes Okaro, Ngapouri (Opouri). :\gahewa, and Orotu, and were probably formed at the same time as the Kaharoa eruptive episode (i e, about 700 years ago). A crater lake also occurs on the summit of the andesite-clacite Mt Edgecumbe (Putauaki), the main cone of which formed between about 5500 and 3500 years ago (date based on tephrochronology; Nairn and Wood, 1987) . The youngest lake in the Rotorua area is Lake Rowmahana which formed after the 10 June, 1886 AD Tarawera eruption (Figure 5.14). Pre\'iousl y, t\\'o shallow lakes, Rowmahana and Rowmakariri, were situated where the modern lake now occurs,

Figure 5.14 The Rotomahana Basin, photographed from near the summit of Mt Tara wera, a few weeks after its shattering formation during the 10 June 1886 eruption. The Tarawera Rift is evident in the foreground. Present-day Lake Rotomahana is shown in Figure 5.15. The photo was taken in late July or early August. 1886, probably by either FM B Muir or A H Burton (Lowe and Green, 1987a). (Burton Brothers, Na tional Museum of New Zealand, Wellington)

Figure 5,1 5 A view to the southwest of present-day Lake Rotomahana , photographed from a position similar to that for Figure 5.14. The lake is now the third-deepest lake in the North Island (112 m). (RM Briggs) Lakes 121

but were destroyed during the phreatomagmatic the past 50000 years (Houghton and Wilson, and hydrothermal explosions that produced the 1986; Wilson, 1986). The Whakamaru-group present basin. Lake Rotomahana, now one of the ignimbrites were previously considered to have North Island's deepest lakes (Figure 5.15), took been erupted from calderas in Lake Taupo, many years to fill, with the maximum level not specifically Western Bay. However, Wilson et al being reached until the 1930s (Grange, 1937; R F (1986) indicate that these ignimbrites were Keam, pers comm, 1987 ). In the associated instead probably erupted from the large Waimangu thermal area to the southwest of Lake Whakamaru Caldera postulated to underlie the Rotomahana, several small lakes, including two Maroa area to the north of the lake (Figure 5.10, I with hot water, li e in craters produced during and Inset), and so were not directly involved in the following the 1886 eruption. formation of the lake basin. Much of the lake owes its form instead to a series of powerful eruptions, LAKES IN THE TAUPO AREA mostly from within the lake basin, in the last 50 000 years, particularly since about 22 000 years Lake Taupo lies within a complex of caldera and ago. fault structures comprising the so-called 'inverse' From about 50000 to 22 000 years ago, five .. rhyolitic Taupo volcano (Figures 5.1 6 and 5.17 ). explosive eruptions occurred from vents within the Inverse volcanoes are concave with the 'flanks' lake basin, ejecting the equivalent of about 10 km3 sloping gently inwards towards the vent locations of magma. About 22 000 years ago, the enormous (Walker, 1984) rather than forming the steep Kawakawa eruptive episode took place in the convex cones characteristic of andesite strato northern part of the lake basin (Figure 5.17 ) volcanoes (eg, Mt Taranaki) or rhyolite domes (possibly in the vicinity of the Whangamata (eg, Mt Tarawera). This inverted form , also Basin), and ejected the equi\'alent of at- least shown by the Rotorua volcano in Figure 5.11 , 155 km3 of magma. The fi nal phase of this eruption arises largely because eruptions from rhyolitic culminated in catastrophic caldera collapse to volcanoes of this sort are typically so powerful form the main structure of the northern part of the that accumulation of erupted material near the modern lake basin (Figure 5.16); Houghton and vent is insufficient to counteract the caldera Wilson, 1986; Wilson et ai, 1986). From 10 000 to collapse due to magma withdrawal, and because about 2100 years ago, at least eight explosive the later effusion of steep-sided domes is compara eruptions, evacuating about 20 km 3 of magma in tively minor. The Taupo volcano slopes inwards total, occurred from north to sou th along the ~ at 1_2°, becomes slightly steeper in places and is eastern side of the lake basin, although this part of .- "cut by faults around much of the lake margin. The the lake may also have been shaped by contempo ...... ' base' of the volcano lies in the lake near the raneous or earlier tectonic downfaulting (Northey, Horomatangi Reefs about 170 m above sea level, 1983). Several submerged rhyolite domes, and and is the lowest point for about 40 km in any Acacia Bay dome near Taupo, are probably direction. The volcano rim, about 50 km in related to some of these eruptions (Figure 5.16; diameter, lies at 600-700 m altitude on the north Froggatt, 198Ia,b; Froggatt and Solloway, 1986) . and northeast sides, thus giving a total relief of The most recent eruption was the dramatic ,,' about 400-500 m (Houghton and Wilson, 1986). Taupo Tephra eruptive episode about 1850 years The Taupo volcano has a long and complex ago, the largest eruption from the lake since the historY which reflects the interactions between Kawakawa eruption. It ejected the equivalent of regional, tectonically-related subsidence and local, 35 km3 or more of magma. The eruption was volcanically-induced collapse (Wilson, 1986). Its centred on the Waitahanui Basin-Horomatangi history can be divided into two major periods: Reefs (Figure 5.16), and consisted of several (I) the eruption of the Whakamaru-group closely-spaced phases, culminating with an . 'ignimbrites; and (2) the more recent period exceptionally powerful and intense ultraplinian comprising a succession of explosive eruptions in eruption (Figure 5.18; Wilson and Walker, 1985) . 122 Landforms of New Zealand

Figure 5.16 Brood structure and topography of the inverse Taupo Volcano with Lake Taupo and the associated Taupo Caldera lying within it. Whakamaru Caldera is postulated to lie to the north (Wilson et 01.1986 ). Numbers mark approximate source vent areas for named Holocene rhyolitic eruptives (otter Froggott.1982): 1. - , Taupo: 2. Mapara; 3. Whakaipo; 4. Waimihia; 5. .' I What'IQamats I Hinemaiaia; 6. MoMere; 7. Opepe; 8. Peronui; 9. Karapiti Basinf ..... ·1 \ ~-, \ . (see also chapter 2). Based on Wilson and Walker (1985). TAUPO '-- ./ ' _ We i;ah8.nUl I '. , ," Wi lson et 01(198 4.1986). and Houghton et 01(1 987). NiFB. CALOERol f J BUij:1 . ,' . COMPLEX \,. -." ~ i... RC!lonia,o Northem Taupo Fault Belt; TVC. Tongariro Volcanic LAKE TAUPO 1.2.3.A'J... • " . ' . Centre. Present lake level is 357 m above sea level. Horomalangi Reefs ' .

Figure 5.17 A southward-looking view of Lake Taupo. New Zealand's largest lake. This tranquil scene belies the lake's explosive history within one of the world's most powertul rhyolite volcanoes. The northem port of the lake is fomned in the Taupo Caldera Complex; in the south it lies in the Southem Graben bounded to the west by the Waihi Fault (see Figure 5.16). The embayed land in the foreground comprises mainly rhyolite lava domes and flows and pyroclastic deposits of the North Taupo Fault Belt; in the background are the snow-copped andesitic 1# Holocane W calders rhyolile dome /' margin stratovolcanoes of Tongariro Volcanic Centre. (D L Homer. DSIR Geology and Geophysics) Lakes 123

(b) Halepe Ash (c) Volcaoogene waterspouf

. • <. ' ~ ~ r .. .'... ' ...... r( r r ( ~

- - \ - 7 '6"'::::,d .. ',~ I t~ id) Aolonga1c Ash (e) Taupo lapiUi (I) Taupo J.;;In imbrite

...... ' ..' I . . . , ......

I ., Figure 5.18 The various phases of the Taupo Tephra eruption about 1850 years ago in the vicinity of the Horomotangi Reefs-Waitahanui Basin area. The eruptive episode resulted in the emptying and subsequent refilling of Lake Taupo, After .. Cos and Wright (1987), based on Wilson and Walker (1985),

! ..- This phase (Figure 5.18e) led to major caldera the eruption. The lake probably took about 10-20 collapse and ignimbrite generation (Figure 5.18f) years to refill, reaching about 30 m abo'Ve its in the vent rcgion within the northeasten part of present level to form several wave-cut benches the large caldera formed by the Kawakawa (Grange, 1937; Wilson et ai, 1986). The lake fell to eruption. The Horomatangi Reefs are probably its modern level when the exit channel, the domes extruded soon after this phase. Waikato River, was re-established (Healy, 1975a). Multiple radiocarbon dates on material asso The northern bays of Lake Taupo (Figure 5.17) ciated with the Taupo Tephra have a mean age of represent a horst and graben fault complex (the 1850 ± 10 years BP, equivalent to a calendar date North Taupo Fault Belt). Some of these faults in the range AD 138-230 (Froggatt and Lowe, have moved since the Taupo eruption and have 1990). A previous calendar date of AD 186, based displacements of up to several tens of metres, ancient Roman and Chinese accounts of although the timing of most of the movement is unusual atmospheric effects supposedly related to uncertain (Wilson et ai, 1986). the eruption of fine ash from the Taupo Tephra In summary, much of the northern part of Lake into the stratosphere, has now been discounted Taupo occupies a complex caldera created largely because of errors in the translations and other during the Kawakawa and Taupo eruptive difficulties (Froggatt and Lowe, 1990). Recent episodes; the southern part of the lake infills a studies of trees buried by the Taupo Ignimbrite at dominantly tectonic graben structure (Northey, Pureora (Clarkson et ai, 1988; Palmcr et ai, 1988) 1983; Wilson, 1986). suggest that the eruption occurred in late summer Other volcanic lakes in the Taupo area include early autumn in the period AD 165-190 Lake Rotokaua, north of Lake Taupo, which nelrh"m AD 17i), matching the range suggested occupies a hydrothermal explosion crater that was from radiocarbon dating. formed possibly about 5000 years ago (Cole and The lakc was essentially emptied during the Nairn, 1975). The lake basin was considerably Taupo Tcphra cruption generating what has been larger beforc the Taupo Tephra eruption and is described as a 'volcanogene waterspout' (Figure now largely infilled with deposits from this 5.18c). A buried wave-cut bench 110 m below the eruption. Lake Rotoaira lies in a fault-bound lake's surface marks an initial lake level soon after basin between the Tongariro and Pihanga 124 Landforms of New leo/and volcanoes dammed by lava flows from Tongariro. including Panmure Basin, Tank Farm, and It is floored by Taupo Tephra, indicating that it Onepoto (eg, see Figure 5.19), have since been was formed earlier than 1850 years ago. A number breached and flooded by the sea but Lake ,Pupuke, of smaller explosion craters also occur (Lowe and which is probably aged 40 000 years or older, Green, 1987a): on Pihanga, Lake Rotopounamu remains as a 64 m-deep maar on the North Shore was formed in the last 10000 years; on Tongariro, (Figure 5.19). Blue Lake (16 m deep) and the Tama Lakes were In Northland, Lakes Omapere and Owhareiti formed about 10000 years ago, and the Emerald both seem to have formed from damming by lava Lakes, occupying phreatic explosion craters, were flows. Preliminary analyses on sediments in cores formed following recent eruptions associated with from Lake Omapere suggest that a lake first Red Crater and are less than 1850 years old formed in the basin roughly 100 000 years ago. (Hackett and Houghton, 1986); near Ohakune, Since then there have been a series of transitory the Rangatau Lakes are younger than 10 000 lakes, most of which were probably very similar to years; and on Ruapehu, Crater Lake (see Figure the modern shallow and weedy lake, but some 11.20), first developed about 1800- 2000 years ago may have been bigger (Harper, 1988). Radio (Palmer, 1991), occupies an active vent and so the carbon dates (Hogg et al, 1987) indicate that the lake basin is being continually modified by volcanic modern lake refilled about 1000 years ago, and activity. An important eruption occurred in 1945 this may have been because of blockage of drainage when an island of molten lava grew to displace the caused by erosion in the catchment, coincident lake entirely. It was then destroyed by explosion with Polynesian habitation and deforestation In and collapse to leave a pit about 300 m deep, New Zealand (eg, Newnham et al, 1989). which eventually filled with water. In 1965, the lake had a maximum depth of 298 m but by 1970 OTHER AREAS it was only 80 m deep at its maximum, probably because of lava moving upwards under the lake. Two lakes, Aroaraotamahine and Te Paritu, OCcur The shape of the lake thus changed from that of a on Mayor Island. Both are effectively dammed champagne glass to a bowl (Hurst and Dibble, like moats against the wall of the Mayor Island 1981). The lake contains hot water (the maximum caldera by a young lava dome extruded into the surface temperature recorded is 60°C) and was centre of the caldera, possibly only a few thousand about 60 m deep in 1983. years ago (Houghton and Wilson, 1986) . On Mt Taranaki, Lake Dive was formed when drainage LAKES IN AUCKLAND AND NORTH LAND was dammed by extrusion of the Northern Beehive lava dome about 3000 years ago or earlier (see These lakes have formed largely as a result of Figure 12.5A). basaltic volcanism. In Auckland, many lakes were formed in craters or dammed against lava flows , but most of these have since been drained, Dune Lakes commonly through crater-wall breaching, leaving Dune lakes are associated with wind-blown sand diatomite or swampy deposits (Searle, 1981 ). deposits, and are particularly common in coastal Western Springs and Lake Waiatarua (Lake St regions. A considerable variety of dune-lake types John) are examples oflava-dammed lakes. Western has been recognised and classified (Bayly and Springs abuts lava flows from Mt Eden and is Williams, ' 1973; Hutchinson, 1957; Lowe and .younger than 20000-30000 years, while Lake Green, 1987a; Timms, 1982). However, these all Waiatarua was formed by lava flows from M t appear to be variations of two major types: Wellington about 9000 years ago (Newnham and 'barrage lakes' and 'deflation lakes'. Lowe, 1991). Other lakes in Auckland lie in basins originating through explosive phreato Dune barrage lakes. There are two main types: magmatic eruptions. Most of these craters, dammed-valley and dune-contact. 'Dammed- Figure 5.1 9 Lake Pupuke, 0 64 m·deep basaltic moor in North Shore City (Takapuna), viewed from the north, The breached Tank Farm (T) and Onepoto (O) explosion craters, which formerly held lakes, are visible to the south, (Whites Aviation, Auckland)

, L valley lakes' arc formed wh en dunes block a from rainfall, is held bv an aquiclude that may . valley draining towards the coast; they vary be formed In \'anous ways (eg, orgal1lc - considerablv in shape but are often rough Iv accumulation, iron pan formation). In triangular-shaped \\'ith the deepest regions close watcrtablc-\\'indo,,' lakes therc is no imper . to the dune dam. or with one or more long meable laye r and a lake forms when the narrow arms up-\'alley from the dune, The sides groundwater le\'c!s are high enough to be of such lakes are typically steep and the exposed in the deflation basin; the lake levels catchments have a relatively high relief. 'Dune thus fluctuate according to the watertable !c\'el contact lakes' occur in depressions between two (the basins hence pro\'ide a 'window' to the or more dunes, or between dune belts, Shapes wa tena ble), vary, but arc typically elongated and relatively Wind-blown sand deposits are abundant on the shallow, and catchments arc usually of low west coast of the ~orth Island, hence most dune relief. lakes occur there. Others arc found on the cast 2 Deflation lakes. These occupy hollows produced coast of the 1'

active frontal coastal dunes that are less than about 150 years old, to moderately weathered, N fixed Pleistocene dunes that rise to elevations of 100-200 m. The mechanisms and timing of dune mobilisation and stabilisation are complex (see chapter 7). In the last 6500 years or so dune belts t formed roughly synchronously along the west coast of the North Island but it is difficult to correlate episodes of dune-building phases between Kaipara Harbour and within different areas because dune deposits may be time transgressive (Bussell, 1988; Shepherd, 1987). Many dune lakes occur at boundaries between dune belts (eg, Figure 5.20) and thus their minimum ages may be determined from the ages of the dunes forming the dams. Most are probably less than about 6500 years old with the exception of those in the Kawhia-Aotea i f Harbours area where they (eg, Lake Taharoa) appear to be older than about 50000 years. Such Tasman older lakes indicate that lakes have probably always been a feature of the dune deposits on the New Zealand coastline, but, because of the Sea dynamic nature of the coast and fluctuating sea levels, have been drained or in filled by successions of later deposits. Some of the modern examples are thus likely to overlie older lake deposits. Most of the dune lakes have not been studied in 1:":\ ~ ' :' j Holocene dune belts enough detail to enable their mode of origin to be categorised, except in some obvious cases, although ~ Pleistocene deposits both barrage and deflation types are probably represented (Cunningham et ai, 1953) . Major groupings occur on the west coast between North o 5km Cape and Kawhia Harbour (Figure 5.1). Those on the Aupouri and Karikari Peninsulas are not well known; near Dargaville, Lakes Kai-iwi and Taharoa are probably dammed-valley barrage Figure 5.20 Dune lakes aligned along the contacts of lakes of mid-Holocene age; on the North Kaipara belts of Holocene dunes. South Kaipora Peninsula. The Peninsula most (eg, Lakes Humuhumu and dune belts hove ages estimated as follows (years BP): 1. Waingata) are likely to be dune-contact barrage 3000-4500; 2. 2000-3000; 3. 1500-2000; 4. 300-1500; 5. <300. After Schofield (1975). lakes of late Holocene age, being impounded by active dunes. The South Kaipara Peninsula lakes include two dammed-valley barrage lakes, being dammed by Dune Belt 3 (Figure 5.20; Ototoa and Kuwakatai: Ototoa, dammed by Schofield, 1975). Those north and south of the Dune Belt I, is about 3000-4500 years old while mouth of the Manukau Harbour (including Lake Kuwakatai, dammed by Dune Belt 2, is about Pokorua and Parkinson's Lagoon) are mid 2000-3000 years old. A string of smaller lakes Holocene or younger and are mainly dune-contact south of these (eg, Lake Kereta) are probably lakes; Wainamu is a dammed-valley lake. Near dune-contact lakes aged 1500-2000 years old, Aotea and Kawhia Harbours, a number of lakes Lakes 127 !

~t . including Parangi, Taharoa, and Harihari arc at different localities many times ID the past " _ dammed-valley lakes impounded by the Te (BusselL 1988). Deposits of the Foxton Dune Akeake Sands which were deposited between Phase, originally considered to have formed about . about 50000-88000 years ago; the sands arc 2000-4000 years ago, may range from 1600- 6000 capped by the Rotoehu Ash (Pain, 1976: Stokes, years in age (Shepherd, 1987: Shepherd and Price. f_ 1987 ), 1990) and so lakes impounded bv these deposits I A second major group of dune lakes occurs (e.g, Lake Horowhenua, a dune barrage lake near • along the Manawatu-Horowhenua coast (Figure LC\'in; Figure 5,21) arc likely to have formed in i ._ 5.1) associated generally with three major dune this period. However, recently obtained radio I belts (the Foxton, Motuiti, and Waitarere Sand carbon dates on sediments in a core from nearby I Phases: Cowie, 1963; sce chapter 13 ). The ages of Lake Papaitonga show that this lake was formed I the dune belts arc broadly known but there is about 8000-8500 years ago, the earliest recorded some uncertainty about the ages of the dunes age associated with the Foxton Dune Phase locally because a period spanning several thousand deposition. Lakes dammed bv the Motuiti Sand t years may have elapsed between the initiation of a Phase are likely to be about 600-1850 years old dune accumulation phase and its final stabilisation and include Lakes Alice and Omanuka. The (Shepherd, 1987; Shepherd and Price, 1990). youngest group was dammed by the \\'aitarere Dune movements probably occurred episodically Sand Phase and these lakes arc about 350-550

Agure 5,21 Lake Horowhenua, a shallow 12 m) dune lake near the town of Levin. Several smaller dune lakes lie tucked in against the extensive hairpin-shaped longitudinal sand dunes in the foreground. The Tararua Range to the east forms the background to the photograph. ID L Homer, DSIR Geology and Gecphysics) 128 Landforms of New Zealand years old; they include both dammed-valley (eg, active aggradation since the last glaciation (sce Lake Heaton) and dune-contact lakes (eg, Lakes chapter 4). Riverine lakes are widespread in these Pukepuke and Pothole). areas and are the second most abundant lake type Further north on the \'Vanganui coast near in New Zealand (Table 5.2). Apart from Lakes Waverley, Lake Waiau was formed by dune Wairararapa and Waikare, they are mostly small movement blocking the Waiau Stream before « 0.5 km2), generally flat bottomed and shallow, about 3500 years ago (Bussell, 1988). usually being only a few metres deep (1-9 m). Other smaller areas of dune lakes are shown in Lateral lakes include Lake Wairarapa, which Figure 5.1. All of these are likely to be of Holocene was a large coastal embayment (estuary) until age. For example, Slipper, Spectacle, and between 2200-4000 years ago when the Tomarata Lakes near Mangawhai were probably Ruamahanga River built an alluvial dam across formed some time before the development of the the seaward end of the embayment, converting it Mangawhai Spit dunefield 700 years ago (Enright into a body of freshwater. This development and Anderson, 1988). In South Westland, the possibly accompanied or followed warping and Tawharekiri Lakes originated within the last 8000 tilting in the region, and the basin occupies a years or so, possibly about 3000-5000 years ago. shallow structural sag with its western margin The dune lakes are small, all being < 5 km 2 in abutting the Wairarapa Fault (Palmer et ai, area; most (> 80%) are < 0.5 km 2 (Lowe and 1989; Figure 16.6). In the historical past, Lake Green, 1987a). They are also generally shallow, Wairarapa was seasonally more extensive than at the deepest lakes being on the west coast of the present. Previously, the lake outlet reached the sea North Island (eg, Lake Waikere has a maximum via Lake Onoke through a bar-gap which would depth of 30 m; Lake Ototoa 29 m; and Lake close during summer (see Figure 5.26). In autumn Taharoa, :\forth Kaipara Peninsula, 37 m ). Some and early winter water le\'els would rise 4 m, lakes have regular or flattish basins (eg, Lake flooding the entire area so that Lakes Onoke and Rotokawau, Karikari Peninsula). Others have Wairarapa joined and the Ruamahanga River irregular basins with channels and sills demar backed up to Martinborough. Levels dropped in cating small basins whic~ tend to lie in the same late winter when the impounded water breached direction along the major axes of the lakes the barrier-bar again (Palm er, 1984). Extensive (Clinningham et al. 1953; Irwin, 1972). lacustrine deposits occur in the vicinity of Lakes Waiararapa and Onoke, and some of these are Rlverlne Lakes probably Last Interglacial in age when a large lake apparently occupied much of the Wairarapa FI'uvial processes can result in the formation of a Valley (Palmer el ai, 1989). variety of riverine (or fluviatile) lakes, the two Many of the lakes in the Waikato region are most important types being 'lateral lakes' and lateral lakes. Most were formed between 'oxbow lakes'. Lateral lakes form when a large 15000-17000 years ago during the final stages of river aggrades faster than its lateral tributaries, aggradation of the Hinuera Formation by the thus resulting in the formation or lateral levees ancestral Waikato River (Lowe and Green, 1987a). which may then dam the tributary drail1 age. The Hinuera Formation comprises volcanogenic Lateral lakes are very common in the valleys of alluvium deposited in the form of a large low larger rivers. Oxbow lakes, also known as angle fan built up by braided channels migrating billabongs, are formed by the cutting off of across its surface (see chapter 10). Lakes were meander loops and in other abandoned river formed between levees adjacent to the channels or channels. A third type is the 'allu vial-fan where levees blocked drainage in embayments in dammed lake' which is usually associated with hills protruding through the Hinuera Formation modified glacial lakes, as described previously. (eg, Figures 10.9 and 10.1 2). Se\'eral short-spaced The lower reaches and flood plains of most New episodes of alluvial deposition are evident in the Zealand rivers have been the sites of extensive and formation of some of the lake basins (eg, Lakes ·!iII' - ~

Lakes 129

FIgure 5.22 Lake Te Koutu (middle right of photo). a shallow riverine loke in Cambridge. was formed about 1850 years ago when Taupo Pumice Alluvium carned by the Waikato River (left) was deposited in the Karapiro Stream valley (lower part of photo). thereby blocking drainage, (M J Selby)

Maratoto, Rotokaraka. and Rotoni1:ata L Sub Tara,,'era Ri,'ers were probablv formed within th e ,equently, many of these lakes ha\'e been further past 1850 and 700 years. respecti"c!Y (\'airn and I deepened by the growth of adjacent peat bogs and Beanland, 1989), I so the lakes in their present form are of complex Although most alluvial-fan dammed lakes ha,'e origin, The detailed dc\'c!opmental histor\' of onc been classed as glacial because the basins of these lakes, Lake :-'lara toto, is shown in Figure originated chiefly as a consequence of glacial (o r 10,11 (Green and Lowc. 1985), early-post-glacial ) activitv, some may well prove ! __ ' Other lateral lakes in the Waikato area were to be entirely flU\'ial in origin. I formed more recently by the deposi tion of the t , Taupo Pumice AIIU\'ium adjacent to the modern Landslide Lakes : Waikato River about 1850 vears ago, and include Lakes Te Koutu (Figure 5.22). \\'aahi, Hakanoa, Landslide lakes form by blockage of drainage In l Waikare, and Whangape, ,'alleys by debris from landslides, Typically, most • Oxbow lakes are common in the Kaihu, landslides tha t form lakes arc rock a,'alanches or :. Manawatu, Taieri. Mataura. Ruamahanga, rock falls that originate from the fai lure of all or , .Wairau, and the lower reaches of the Clutha River part of a mountainside, and fall rapidly from the 'valleys (Figure 5,1: Cot ton. 1958), All these lakes ridge crests into the ,'alleys, piling up against the 'are likely to be of late Holocene age because thev far ,'allev walls (Adams. 1981 a; Costa and - lie on recentlv aCli\'C flood plains an d hencc may Schuster. 1988; Whitehouse, 1983: sce chapter 3), be subj ect to frequl'nt flooding and sediment in The resultant hummockY deposits. usually lobatl' .'filling, Small lakes on the Rangitaiki Plains (Bay where not confined by local topogra ph\'. may 'of Plenty) associatl'd "'ith the Rangitaiki and resemble glacial moraines but differ from them b\' ~l. 130 Landforms of New Zealand being asymmetrical about the "alley axis. b,' the causes (Costa and Schuster, 1988; ''''hitehouse presence of swash features and debris on "alley and Griffiths, 1983) . sides, and the SOurce scar above the deposit Landslide lakes are generally short-lived because (Whitehouse and Griffiths, 1983). In addition. they may rapidly infill with sediment eroded from they contrast with moraines in containing a j umblc the catchment, or the river filling the lake may of large blocks and open crevices and may also wash out or overtop the landslide dam. Often the include abundant remains of trees and other breaching results from headward stream erosion vegetation that once grew on the pre-Iandslide starting at the toe of the dam. On this basis, slopes. Landslides arc always associated with Adams (198 Ia) has distinguished two types of areas of steep terrain. The main tri ggering landslide lakes: 'temporary lakes' on large rivers mechanism is seismic activity (earthquakes), but that are soon destroyed, and 'permanent lakes' on intense rainfall and snowmclt arc also kn own tributaries that may remain for thousands of years. The permanence of the lakes depends mainly on the size of the landslide and the size of the river Figure 5.23 Lake Constance. a landslide lake at 1300 m a ltitude lying within a once-glaciated valley near the dammed, and even very large landslides are headwaters of the west branch of the Sabine Valley. The unlikely to dam the largest rivers permanently. lake is impounded by a huge rockfall from the Franklin In ~ew Zealand, the active tectonic environ Ridge (mar1

t . • - . Goroe cl ~ Vlaikarelaheke "... = Pvkelapu I River : ::Si •. " ,. I Escarpmef\1 NE i 'l~-;~ .: a b c • ~1l~ .. ~I/ /'Lake Matiri is a landslide-dammed lake on the bably took about 10 years t~ fill (Marshall, Matiri River north of Murchison. About 15 X , and has the V-sided basi~ and dendritic 106 m3 of rock and fine debris fell 600 m from the ~hc)reline typical of most landslide lakes occupying western slopes of the Bald Knob Range, damming valleys (Irwin, 1975b; Mai'1 1976). Lake the valley to a depth of about 30 m around 300 132 Londforms of New Zealand years ago. The lake is now only 20 m deep because of subsequent infilling by a delta at the north end of the lake and hence has a predicted total life of less than about 700 years (Figure 5.25; Adams, 198Ia). Lake Matiri and seven other small pre historic landslide lakes in the Buller area are thought to have been formed by a past earthquake because of their proximity and similar character istics to the lakes formed during the 1929 Buller earthquake (Adams, 198Ib). Lake Christabel, on the uppermost Grey River, I 77/7 11111 C 1000yr B P is probably landslide-dammed (Figure 5.25). Suggate (1965) considered the barrier to be a glacial moraine, but it lacks the smooth outwash surface that normally extends downstream of young moraines in other parts of the South Island Chalice 100: - (Adams, 198Ia). The barrier contains large angular blocks of schistose greywacke and its L o 1 2 km permeability seems high. About 80 per cent of the normal flow of the Grey River passes through the Figure 5.25 River bed cross-sections of four South Island landslide-dammed lakes. based on topographic maps; barrier, appearing as springs downstream of it. lake bathymetry is sketched in. Age of lake formation is The age of the lake is uncertain. Trees several indicated. After Adams (19810). hundred years old cover the barrier and the amount of sediment in the lake seems more likely similar to the largest described on earth, the to represent about 1000 years of catchment erosion 2 x IOlO m3 Saidmarreh landslide in Iran rather than the 10 000 years or so if the lake is of (V"'hitehouse, 1983). Lake Lochnagar is dammed 6 3 glacial origin (Adams, 1981 a). by a 270 X 10 m rock avalanche derived from a Lake Chalice, on the Goulter River west of lOO-m thick slab of schist which slid along a plane Blenheim, was formed by a lOO-m high landslide of schistosity. barrier about 2200 years ago (Figure 5.25). The sides of the lake basin are very steep and slope at Barrier-Bar Lakes 60°. The lake level is about 15 m below the lowest 'point on the landslide and the lake drains under These lakes form through the enclosure of inlets or ground through the barrier so that the lake level embayments or estuaries by barrier-bars or spits. fl uctua tes considerably. The barriers originate by wave action, often In the Southern Alps between Arthur's Pass coupled with sea level fluctuations or tectonic and Mt Cook, 46 Holocene rock avalanches of movement, and are thought to have formed indurated sandstone and mudstone, with volumes mainly through marine reworking of alluvial 3 ranging from I million to 500 million m , are gravels and sands during the Holocene post-glacial known and some of these have formed lakes transgression. Gravel-pebble (shingle) barriers (Whitehouse, 1983; Whitehouse and Griffiths, predominate where there is a large gravel input 1983). Such rock avalanches have also formed into the littoral system (see chapter 7). The lakes lakes in the southwest part of the Southern Alps. usually occur adjacent to river mouths near the Lake Adelaide is formed by a massive granite sea and most therefore lie at low altitudes « landslide whereas Green Lake was formed by a 30 m) on the coastline, as lagoonal features. gneissic rock avalanche. The latter is the largest In the North Island they are found along the known rock avalanche in New Zealand, and has a Wellington-Palliser Bay coastline (eg, Lake volume estimated to be 1.4 X IOlO m3 which is Onoke, Figure 5.26) and near the Wairoa River La kes 133

near Gisborne (eg, Whakaki Lagoon). In the (Ota et ai, 1989 ). Lakes Kohangatera and South Island, where the)' occur more frequently, Kohangapiripiri, near Wellington, originated as barrier-bar lakes predominate on the east coast, drowned inlets through sea levcl rise and down particularly Marlborough (eg, Lake Grassmerc), tilting before about 6500 years ago. The inlets Canterbury (eg, Lakes Ellesmere and Forsyth), were cut off by shingle spits then bv gravel barriers and Dunedin (eg, Wainono and Tomahawk widened by successi\ "C uplift since about 3100 Lagoons). Others arc in Wcstland (eg, Lake years ago (Figure 5.27; Ste\TnS, 1973 ). Lake Windemere) and on Ruapuke Island in FO\'eaux Onoke, impounded against allU\'ium deposited bv Strait. Te Whanga Lagoon and various other lakes the Ruamahanga River, was probably formed on Chatham Island probably originated through around the same time (4000- 5000 years ago); barrier-bar impoundments (Allan, 1928; Hay et ai , nearby Lake Pounui (Figure 5.26) formed about 1970). Several barrier-bar lakes occur within larger 2500 years ago or earlier (G 1\·1 Turner, pers lakes, including Onewhero Lagoon, whieh is comm, 1991 ). Lakes Grassmere and Ellesmere, on separated from the eastern shore of Lake Rotoma the Marlborough and Canterbury coasts re spec by a wave-formed shingle and sand spit, and Lake ti\'ely, de\'c1oped in se\'eral stages: an initial phase ~ Rotongaio on the eastern shore of Lake Taupo. of spit growth enclosing a marine bay followed by . All the barrier-bar lakes are probably of extensive shoreline reorientation by erosion and Holocene age. The few studies that have been accretion since about 6000- 7000 vears ago done indieate that they generally attained their (Armon, 1974; Figure 7.9). Lake Forsyth, near present form within the last 6500 years or so when Lake Ellesmere, has apparently been permanently sea level reached its present position (Gibb, 1986). impounded since early European settlement (by Whakaki Lagoon formed since about 4000 years barrier 4, Bi rdlings Flat; Figure 7.9), pre\'iously ago by the closing of an estuary by a sandy barrier being open to the sea. Thus the present lake may

Rgure 5.26 Lake Onake. a barrier-bar lake fed by the Ruamahanga River on the south Wairarapa coast adjacent to . ~alliser Bay. Lake Pounui is a lso visible in the low hills in the background. which rise to form the Rimutaka Range. (M R Balks) t a

134 Landforms of New Zealand be only 150 years old. If the older barriers (1-3) N previously extended right across the inlet of the basin, then the lake may have existed in earlier . .L ~ -" __ _ . ... Jl .i..-: periods until the barriers were breached. Gage t ... (1980) suggested an age of about 1000 years for . , Lake Forsyth's cut off. :f/, 2 Most barrier-bar lakes are small « 0.5 km ) but two are relatively large: Lake Ellesmere '.. . _ ...... -A- - ...... 2 2 (182 km ) and Te Whanga Lagoon (160 km ). ..01... _ ..... -"'--, ,/" ...... JL \ They are typically shallow (1-5 m) and D-shaped or oval, but may have irregular outlines on the inland margins. Sizes and depths can vary con siderably because of fluctuations of lake level A through tides, and changes in outlet configuration. The coastal barrier-bar lakes are commonly brackish (New Zealand's table salt is produced by evaporation from Lake Grassmere). Some may o 100 200 m remain landlocked until they fill to certain levels ! t "' when channels are cut through the barriers and A Ol(ler beech rIOOe B waters drain out to sea (eg, Te vVhanga Lagoon and bench 1855 b&Ilch rlOQe A 10 u. Oldef lake IevClI 1855 lake I\tv81 l~ m breaches naturally in approximately seven-year Mean . .. ' '. . i I --, - ...... > cycles), although levels may be controlled artifi 1855 shoreline Oloer ahoreline ~3.0 m Form ... lake - 5.B m cially (eg, Hughes el ai, 1974). ""' .. Figure 5.27 Map and crass-section of beach ridges an Tectonic Lakes gravel barrier-bars impcunding Lake Kahangatera. Pencarraw Head. Wellington. The 'Older beach ridge', Tectonic lake basins, formed wholly by movements uplifted about 600 years ago, was farmed after about of the earth's crust, are very uncommon in New 3100 years ago. An ea~ier lake may have existed in the Zealand, but various lakes modified by displace area because gravel beach ridges aged about ment of the ground surface are better known. 3100-6500 years occur close by an this coast, After Stevens (1973). Most of these occur in the seismically-active Hawke's Bay region in the North Island (eg, Lakes Ellery, Kaurapataka, Sumner, and Brunner, Lakes Hatuma, Poukawa, Runanga, Horseshoe, are thought to have been influenced by faulting. and Rota-a-kiwi) (Lowe and Green, 1987a). All In Dismal Valley near Lake Sumner, for example, are modified to some extent by alluvium or peat vertical and horizontal movement on the active deposits (eg, as described for Lake Poukawa by Kakapa Fault has resulted in the formation of a Harper el ai, 1986). Lake Wairarapa has in the small, unnamed tectonic lake, referred to as a past been regarded as one of New Zealand's few fault-pond by Yang (1991). Thus, while definitive tectonic lakes (Cotton, 1958), but it is now 'known tectonic lakes are few, many lakes in New Zealand to be a riverine lake (see above). A series of small have been formed as an indirect consequence of ponds near Waimangu, in the Rotorua district, all the country's pervasive tectonism (eg, those formed < 1 ha in area, have formed where the slopes of by earthquake-induced landslides and most the Earthquake Flat Crater (see Figure 11.11) volcanic lakes). have been cut by a fault downthrown on the up slope side. All the little erosion valleys thus Solution Lakes truncated have tectonically-produced ponds at the fault (RF Keam, pers comm, 1987). Solution lakes - sometimes called karst lakes Several South Island lake basins, including occur in karst terrains in which carbonate rocks, Lakes 135

mainly limestones and marbles, have been lakes (Lowe and Green, 1987a), may sometimes dissolved by percolating natural waters to produce form when rapidly-growing vegetation impedes .... a characteristic landscape (see chapter 8). In such drainage, in a similar way to the formation of • areas, most solution occurs by rainwater falling on lateral lakes by alluvial deposition. Grange et al and descending through the carbonate rocks to (1939) suggested that some of the lakes around .. form corrosion hollows. As well, subsurface the peat bogs in the Waikato region may have streams enlarge cavities which may collapse to formed in this way, but this has not been sub produce depressions. These basins may be of stantiated (Green and Lowe, 1985). Peat growth various sizes and shapes: dolines are funnel- has contributed to the later stages of development ,_ shaped; uvala are formed when adjacent dolines of these lakes, however (chapter 10). fuse; and poljes are large karstic depressions. Any Some of the dozen or so small lakes in peat bogs of these may fill with water to form a lake, which on the Chatham Islands, such as Lake Rotokawau, may be ephemeral if the water is periodically lost may have formed in hollows in the peat surface when drainage through cracks and joints in the resulting from peat fires (Allan, 1928; Wright, underlying rock material is greater than input by 1959). These fires have been known to burn for ,,' precipitation. many years, producing holes about 3 m deep. ( :,. ~ Solution lakes are rare in New Zealand, re Ponds and small lakes may also develop in . -' flecting the relatively uncommon occurrence of hollows on peat surfaces formed by spatial karst landscapes. The largest solution lake is Lake variation in rates of peat deposition. Such vari Disappear (see Figure 8.3), which periodically ations may be caused when differences in occupies a polj e associated with Tertiary carbonate subsurface relief affect the supply of soligenous ....= rocks in the western King Country area near water (mineralised ground water) and thus the Aotea Harbour. The polje is flooded after heavy development of ombrotrophic, or peaty, conditions rainfall when the flood inflow is greater than the (Boatman et ai, 1981 ). This process may be drainage can discharge. The lake fills to a depth of operative in New Zealand, and two examples arc about 15 m. Other small lakes in dolines (eg, Lake the lakelets within the Kaipo Lagoon peat bog •. Koraha) occur in the limestone country south of and other montane bogs near Lakes Waikareiti Kawhia Harbour and north of Raglan Harbour. and Waikaremoana (Lowe and Hogg, 1986), and Small, perhaps periodic, solution lakes probably the many pools within the Lagoon Saddle mire occur in limestone or marble terrains in the near Mt BTUce, Canterbury (Dobson, 1975). In Hawke's Bay, Wairarapa, Nelson, and South both cases, the pools are less than about 10 000 Canterbury regions (eg, see chapter 19). For years old; those in the Kaipo Lagoon are possibly i -: example, roughly circular snow-filled dolines in about 5000 years old. Lakelets and small pools j...... tli.e Mt Owen region presumably form small lakes also occur frequently in the Kopouatai peat dome I' ~ after snowmelt (chapter 8). Lake Marakapla and in the Hauraki region, and in the Ahukawakawa i Lake Rotoparaoa, and several others, on Chatham Swamp in Taranaki, and many of these could i Island are thought to have formed initially as probably be classed as peat lakes. I' .doline solution lakes but may have been sub . sequently modified by sand-dune barriers (Allan, Artificial Lakes -1928; Hay et al; 1970). I '. . Most of these lakes date from this century, many .:-,r.;" " Peat Lakes since the 1950s. In general, large artificially dammed lakes provide storage for hydroelectric . . Although many lakes have been secondarily power generation, and many small artificially ".: affected by peat development, there are few dammed lakes, including farm ponds, are , blown New Zealand examples of lake basins that reservoirs for urban and rural water supplies or .. have resulted primarily from organic accumula irrigation systems. Other types include those tions. Such peat lakes, also known as phytogenic formed by flooding of worked-out open cast mines, 136 Landforms of New Zealand

Figure 5.28 Lake Karapiro, viewed from the north, is an artificial hydroelectric lake on the Waikoto River formed in 1947. It has a maximum depth of about 31 m. (MJ Selby) quarries, or deep holes exca\'ated bv hydraulic SUMMARY elevating in the pursuit of gold (eg, Bluc Lake, St Bathans, Central Otago). Small lakes may be ~ew Zealand has a great \'ariety of lake types formed by excavation of low-lying swampy ground within a small land area as a result of its activc for recreational or aesthetic purposes (eg, tectonic regime, its recent volcanicity, and the Knighton, Oranga, and Chapel Lakes on the effects of repeated Pleistocene glaciations, which University of Waikato Campus, Hamilton). together have produced an earthquake-prone, The major North Island hydroelectric lakes generally rugged and youthful landscape conducive occur on the Waikato River, draining Lake Taupo to the formation of lake basins. The broadly (eg, Figure 5,28); in the South Island, most occur localised distribution of geological processes has on the Waitaki and Clutha River systems (Figure resulted in geographical groupings of ten main 5,1). Lake Benmore, on the upper Waitaki River, lake types into distinct lake districts : for example, was formed in 1965 and is New Zealand's largest volcanic lakes are restricted to the ~orth Island, artificially-dammed lake (74 km') and has a maxi glacial lakes to the South Island; wind-formed mum depth of91 m. The nearby Lake Ruataniwha dune lakes occur mainly along the west coast of on the Ohau Ri\'er was filled in 1982. Lake the ~orth Island; and ri\'Crine lakes arc pre\'alent Rotorangi, an earthdam-impounded lake on the on the flood plains on the major river ri ver S\'stems Patea River near \\'anganui. was filled in 1984 of both islands. The :-';orth Island has a pre and is the longest (46 km ) artifici all y-dammed dominance of small dune and ri\'Crine lakes and of lake in New Zealand, with a maximum depth \'olcanic lakes in the central \'olcanic region. The of 58 m. South Island has a predominance of glacial lakes, Il ¥:

Lakes 137

many at high altitudes, and of riverine lakes. are about 16000 years old; and a few of the dune Other lakes occur in small numbers throughout and volcanic lakes which are about 50 000 years . . the country and include landslide, barrier-bar, or older. Younger lakes include several volcanic tectonic, solution, peat, and artificial lakes. Many lakes, probably all of the landslide lakes, and lakes have multiple origins and have been affected many of the riverine, dune, and barrier-bar lakes. by more than one geomorphological process Almost all the artificial lakes have been formed following their formation and so have complex this century. developmental histories. The bathymetry and morphology of the lake Most of the lakes are young, and many are aged basins are generally well known, all the major

: < between about 5000 and 10000 years. Some are lakes having been surveyed in detail. ". older, such as the Waikato riverine lakes which

REFERENCES

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