VOLCANIC SHOWERS

Evening Star, Issue 20993, 6 January 1932, Page 12

VOLCANIC SHOWERS

INFLUENCE ON NORTH ISLAND SOILS MOSTLY BENEFICIAL [From Odr Correspondent.] WELLINGTON, January 6. Over twenty-one thousand acres of North Island soils are carrying on the surface the product of ancient volcanic eruptions, and these showers of debris have an important effect on farm production and the health of stock. Two volcanic showers consisted of elements which have certain chemical deficiencies, and for thirty years have caused trouble to stock raisers through what is popularly called “ bush sickness.” In the course of a very thorough survey of the disease of bush sickness, conducted by Cawthron Institute chemists and officers of the New Zealand Geological Survey, the volcanic showers which have so greatly influenced modern farming in the North Island, are enumerated. This section of the bulletin gives a very interesting glimpse of the geological history of the North Island. At least three great centres of volcanic activity have been concerned, and the soil survey only notes those where ash showers were deposited on what is the present surface, thereby constituting the present material from jvhich the soils have been formed. EIGHT VOLCANIC SHOWERS. The soil survey of the centre of the North Island recently conducted by the Department of Scientific and Industrial Research enabled eight volcanic showers to bo definitely traced. Their influence extends from Hamilton to Taihape, and across the island from New Plymouth to near Gisborne, covering an area of about 21,000 square miles. Eight distinct showers have been identified, all of which give rise to soiis of distinct properties, and some striking differences wore noted. It was-found that a very superficial coating of some of the ash showers greatly changed the quality of the land for farming purposes, and it seems clear that the Tarawera eruption, by throwing a coating of ash over certain areas previously covered by an earlier eruption from a. different source, removed from the land so covered the risk of stock contracting bush sickness. Two volcanic showers spread ash which is chemically deficient in the constituents for healthy life of stock. These are the Taupo shower and the Kaharoa. The former is most widespread. It had its origin in Lake Taupo, and spread chiefly to the westward. The ash is rhyolitic in composition, contains a good deal of pumice, and is coarse in composition. The Kaharoa shower, composed of rhyolite fragments, came from a crater south of Lake Rotiti, and extends north to Tauranga, and south to To Whaiti. This also is very coarse in texture. THE BENEFICIAL SHOWERS.

The geologists note six ash showers which rained on the future farming country soil elements of value. In their geological order they are described thus;—

The Mairoa shower, dark brown in, colour, occurs in Te Kuiti, Mairoa, Te Awamutu, and Kawhia districts, and is derived chiefly from Egmont, an andesite volcano, together with some rhyolite from the Rotorua and Taupo centres This soil is in the loam category, and well leached of lime, magnesia, and soda.

The Egmont showers comprise at least two showers of different epochs. The older, ash,’ dark brown in colour, and speckled with crystals of felspar, extends northwards to Aria and southeast. to Wanganui. The younger ash extends from the mountain eastwards as far as Stratford. The Tirau shower, which forms the base of the soils of Tirau and Putaruru districts, is rhyolitic in composition mixed with a little andesite. It resembles the Mairoa soil in appearance and texture.

The Tongariro shower, erupted from the andesite volcano of that name, was blown a long distance to the north to near Putanxru, and eastwards to near Napier, but in these directions is covered with Taupo pumice. Southeast of Tongariro it forms the soil along a narrow belt extending from Raetihi to Napier. Ngauruhoe ash, andesite in composition, occurs within a circular area of about thirty miles radius around the volcano. Ash and scoria from presentday eruptions continue to add to the thickness of the deposit in some localities, and dust from one of these eruptions was carried ten miles to the northeast, on the llangipo prison farm. The most modern of these ash showers is that of Tarawera, which erupted in 1886. It extends a short distance south-westward, reaching nearly to the Eotorua-Waiotapu road, and to the north-east to Whakatane. The deposit is made up of two different kinds of ash. East of a line joining Lakes Rcrewhakeitu (south-east of Lake Tarawera) , and Okataina, it consists of dark basalt lapilli forming a very coarse soil, whereas to the west of the lakes it is grey mud, a loam in texture, composed of rhyolite ash with a small admixture of basalt. The opinion of the research workers is that this particular beneficial ash shower, and that from Ngauruhoe, where it fell on the area of the Taupo shower, may profoundly affect the properties of the underlying soil, rendering it healthy to stock.