VOLCANIC SHOWERS

Rotorua Morning Post, Volume 1, Issue 125, 19 January 1932, Page 7

VOLCANIC SHOWERS

INFLUENCE ON NORTH ISLAND SHORES BENEFICIAL. EFFECT ON FARM PRODUCTION WELLINGTON, Jan. 6. Over twenty-one thousand acres of North 'Island soils are carrying on the surfaee 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 hush sickness, conducted by Cawthron Institute ehemists 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 seetioxl 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 surfaee, thereby constituting the present material from which 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 enablgd eight volcanic showers to be 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 identifled, all of which give rise to soils of distinct properties, and some striking differences were 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 Lalce Taupo, and spread^chiefly to the westward. The ash is rhyolite 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. Rotoiti, and extends north to Tauranga, and south to Te Whaiti. This also is very coarse in texture.

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 eolour, oceurs 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, J magnesia and soda. :

The Egmont showers comprise at least two showers of different epochs. The older ash, dark brown in colour, and speckled with erystals* of felspar, extends northwards to Aria and south- ; east 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- rhyolite in composii tion mixed with a little andesite. It ! resembles the Mairoa soil in appearI ance and texture. I The Tongariro shower erupted from i the andesite volcano of that name, i was blown a long distance to the north ; to near Putaruru, and eastwards to ! near Napier, but in these directions is covered with Taupo pumice. South- ! east of Tongariro it forms the soil along a narrow belt extending from Raetihi to Napier. Ngauruhoe ash, andesite in composition, occurs writhin a circular area of about thirty miles radius around the volcano. Ash and scoria from present-day 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 north-east, on the Rangipo 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 Rotorua-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 Rerewhakaitu (southeast 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 partieular 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.