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A SURVEY OF THE KETETAHI HOT SPRINGS

By G. Rennison and J.L. Brock

A B S T R A C T

The setting and history of the Ketetahi Hot Springs area are outlined briefly.

The methods used in the mapping of the area, which was carried out in January of 1968, are described.

A map of the area at the head of the Mangatipua Stream and a table describing the major vents located on the map are presented. The results are discussed in relation to other work carried out in the area.

I N T R O D U C T I O N

Ketetahi Hot Springs is an area of thermal activity located at a height of 4,500 feet on the northern slopes of North Crater, Mt. Tongariro. The springs area embraces the upper reaches of the Mangatipua Stream as well as several smaller adjacent areas of thermal activity. The area is readily accessible by track (three hours walk) from the National Park Rangipo Highway, and a new National Park Board Hut has recently been built fifteen minutes walk away from the springs. Although the area enclosing the springs is not gazetted as National Park and is still Maori land, access is freely available at all times.

H I S T O R Y

A more complete account of the history of Ketetahi is given by Gregg (1960) in "Volcanoes of Tongariro National Park", pp 62-64. The following is a short summary of the above.

Ketetahi was well known to the Maori for many years before European entry to the area, and the waters of the springs were used as a curative for many skin complaints, rheumatism etc. Bidwill in 1839 saw large volumes of steam from Ketetahi, which was also noted by other early observers such as Hochstetter, Crawford and Hector in the 1860's. Kerry-Nicholls who visited the springs in 1883 produced the earliest known description of the springs. Although extremely colourful, his description would still be accurate today. Later, in 1888, Thomas recognised Ketetahi as being the enlarged head of a gully rather than a crater.

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There is no evidence that there has ever been a major eruption from Ketetahi. Increased activity has been reported on many occasions, notably 1894, 1927 and 1945, but most of the variation in activity can be related to changes in atmospheric humidity which can cause great variation in the size of the steam cloud.

M A P P I N G O F T H E H O T SPRINGS

Very little accurate mapping has been carried out in the Hot Springs area. A rough survey was made in December, 1940, which was concentrated in the valleys of the Mangatipua and Rangihiroa ("Grotto") Streams. At this time an apparent westward extension of the thermal activity was noted. Description of the important vents within the main basin (Mangatipua Head Waters) was made, temperatures taken and detailed analyses of spring waters was carried out at Wellington (Wilson 1960). As little subsequent work has been carried out in the area up to January 1968, it was felt that accurate mapping of vent location at the head of the Mangatipua Stream was needed to:-

a) Provide a picture of the pattern of activity today, and

b) Provide a base against which future work in the area can be compared.

In addition, information on vent size and the nature of ejecta would be obtained.

M E T H O D S

Mapping was carried out using prismatic compasses, a 100ft. nylon tape and "Suunto" slope measuring devices. The walking track (poled) through the centre of the springs was used as a major base line and wherever possible, the location of a vent was recorded as a bearing and a distance from known point on the base line. Where a distance measurement was impracticable, a cross bearing on the vent from two points on the base line was made. To enable a good closure of the whole survey to be made, prominent features on the rim of the valley were surveyed in by cross bearings from the base line and related to the compass and tape survey which extended two thirds of the way round the entire valley.

Important features such as large crateral areas, large mud pools, which could not be mapped by a simple bearing and distance as could the smaller features, were located by a series of bearings and distances or series of cross bearings. Areas of diffuse activity (steaming ground, without active vents or fumaroles) were located approximately. In addition to the mapping, photographs were taken covering the main areas of activity and geomorphic features.

F I G . 1 Wide angle view of the Mangatipua Valley looking northwards. Vents 1-8 upper right, vents 46-50 lower right corner.

F I G . 2 Close up view of central part of the Mangatipua Vents 25-38 centre left. Poled track runs through the centre.

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R E S U L T S A N D DISCUSSION

The map records the main geomorphic features and areas of activity at the head of the Mangatipua Stream. Elevations are not given on the map but the difference in elevation between points 1 and 52 would be approximately 260 feet. Table 1 presents more detailed descriptions of the individual vents indicated by numbers on the map.

Three main centres o f strong activity were noted. One occupies a basin at the foot of the valley (vents 1 - 8) with a subsidiary basin above (vents 10 and 11). The other two are located in the area round the central stream. The lower and less active of these two areas contains vents 17 to 24, while the upper area (vents 30 to 38) has the strongest activity in the valley in vents 33 and 34. These find­ings approximate closely those of the 1940 survey (Wilson 1960).

Two other areas where little or no steam or water emission was occurring, but where the ground was generally hot to the touch and rang under the feet, were noted. One was around the area of vents 40 to 44, and the other half way along the top of the ridge on the eastern rim of the valley, Large areas of warm steaming ground with sulphur deposits were widespread particularly on the valley walls.

The only evidence of recent changes in activity were noted at vent 14 where mud had been ejected to a 6 foot radius round the vent, and at vent 6 where activity had decreased since a visit in September 1967, the level of mud being approximately 1 foot lower when recorded in January 1968.

No geyser activity was noted from any of the areas despite the many hours spent in the valley observing vent activity. The position of the Great Ketetahi Blowhole as noted in the 1940 survey by Wilson would appear to be unchanged and is still the most active vent in the valley (vent 34).

C O N C L U S I O N S

It is felt that the survey will be useful to future workers as a reference point for further work in this area. According to reports (pers comm.) by the Tongariro National Park Rangers, it appears that the area of thermal activity on the slopes of North Crater is increasing and it will be interesting to relate increases in size to activity in the main valley.

It is also interesting to note that increased activity in the springs area has occurred at the time of eruptions from Ruapehu, Ngauruhoe or Tongariro (1894 - Te Mari , 1927 - Ngauruhoe, 1945 - Ruapehu). Inspection of Ketetahi after a future eruption in the area would be well worth while.

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R E F E R E N C E S

G R E G G , D.R. 1960 The Geology of Tongariro Subdivision. Bull. N.Z. geol. Surv. n.s. 40.

1960 "Volcanoes of Tongariro National Park". N.Z. geol Surv. Handbk. i.s. 28. pp. 62 - 64.

W I L S O N , S.H. 1960 "Physical and Chemical Investigation of Ketetahi Hot Springs". Bull. N.Z. geol. Surv. n.s. 40. pp .124-44 .

T A B L E 1 : Description of the major vents located on the Map of the Head of the Mangatipua Stream.

Vent No. Dimensions Description

1 Circular - 3' diameter Low pressure steam

2 Triangular - 16' x 6' — Black boiling water emptying into stream

axis 75QN

3 Circular - 6' diameter High pressure steam — 1 main vent, 2

lesser.

4 Circular — 3' diameter Feeble blue mud spout

5 Circular - 2' diameter Very low pressure steam

6 Oval. 2 5 ' x 15'. 6' deep Mud and hot water in subsidary crater at

axis 160°N northern end — steam at southern end.

7 Two vents in stream bed High pressure steam

8 Circular — 7' diameter, Low pressure steam

inner vent 2' diameter

9 Cluster of small sulphur depositing vents.

10 Circular depression — Medium pressure steam vent partially

25' diameter blocked by rocks — noisy

11 O v a l - 2 ' x 1' Medium pressure steam

12 _ _ _ _ _ _ _ Medium pressure steam amongst rock

13 Oval - 3' x 1W Bubbling blue steam and mud

14 Circular — 3' diameter Bubbling blue steam and mud

15 Circular 2W diameter Bubbling blue mud

16 _ _ _ _ _ Low pressure steam from small fissure

17 Circular — 2' diameter Medium pressure steam and boiling water

— some sulphur deposition

18 Boiling water and steam jet in creek bed

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Vent No. Dimensions Description

19 Boiling water and steam jet in creek bed

20 Large volume high pressure steam

21 Noisy high pressure steam

22 Low pressure steam in creek bed

23 Low pressure steam in creek bed

24 Large volume low pressure steam in creek

bed

25 Oval — 6' x 2'. axis Boiling water, western end only

2 2 5 ° N

26 Steam and water jet in creek

27 Circular — 5' diameter Low pressure steam and boiling water -

sulphur deposition

28 Circular - 1' daimeter Steam and water jet blowing 4 - 5' high

29 Circular — 1' diameter Low pressure steam

30 Circular — 8' diameter High pressure steam and vigorous water

jets in stream

31 Circular — V/i diameter Mud and sulphur deposit

32 Circular — 15' diameter Medium pressure steam

33 Oval - 15' x 10' crater High pressure steam - Noisy

34 Circular - 15'diameter High pressure steam - noisy — largest

in valley

35 Low pressure steam and sulphur deposit

36 Boiling water in creek — sulphur deposit

37 Low pressure steam

38 Low pressure steam in creek

39 Low pressure steam

40 Black water and sulphur deposit

41 Circular 4 " diameter Boiling water jet to 1' high

42 Circular - 9" daimeter Boiling water jet to 1' high

43 Boiling water and steam from several

points round a large rock

44 Large area approximately Medium pressure steam and sulphur

100' diameter deposits. Area very hot, boiling water and

small streams in many places.

45 Oval - 3' x 2' Low pressure steam surrounded by dry

white mud

46 Circular - 8" diameter Low pressure steam and sulphur deposit

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Vent No . Dimensions Description

47 Circular - 4 ' diameter Low pressure steam

48 Circular - 8" diameter Low pressure steam and sulphur deposit

49 Medium pressure steam and water blown

to 15' radius over rocks

50 Medium pressure steam

51 Circular - 6 " diameter Low pressure steam. Sulphur deposit

52 Circular - 6 " diameter Low pressure steam. Sulphur deposit

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KETETAHI HOT SPRINGS JANUARY 1968

100 200

Scale in Feet

LEGEND

Poled walking t rack

•23 Vent X . S c a r p

>Seconda ry scarp

C l i f f ^^IK^ Stream

Ridge- top

Mangatipua Stream

52 IxliLLiilAdi^-

V- Photographs taken f rom here