VOLCANIC ASH

Nelson Evening Mail, Volume LXVI, 17 June 1932, Page 7

VOLCANIC ASH

THE BRIGHT SUNSETS THEORY EXPLAINED In a conversation with a “Post” representative, Dr. E. Iviclson, Director of Meteorological Service, explained further his theory that the bright sunsets'of late have been the result of the eruption of volcanoes in Chile, and incidentally cleared up some misconceptions about his theory. “There appear,” he said, “to be a number of misconceptions with regard to the volcanic ash which has been obscuring our atmosphere for the past month. In the first place, it has been said that the idea that ash should have come so far is far-fetched. But it must be remembered that after the eruption of Krakatoa the ash spread over the whole globe, producing effects similar to those seen lately. The eruption of Tarawera also produced effects on a somewhat smaller scale, right round the earth. Papers received recently from England show that directly the eruption was reported it was realised that a distribution of the ash over the globe was to lie expected, and they will be looking for abnormal sunset effects in England.

“Again, it lias been suggested that White Island might be the source of the ash. This could not, in any case, be so without the fact being obvious. If White Island were able to produce effects as marked as they have been in the south of New Zealand, something much more notable must have been observed in the Bay of Plenty. But any discharge from White Island must ho significant, and what there was would have been carried away in llie westerly winds long before it could have reached the southern provinces. It. must be remembered that six volcanoes were simultaneously in active eruption in Chile, and some cubic miles of rock were shattered and blown into the air.

“The next misconception is that the asli has arrived at New Zealand by the short route. This is impossible in the prevailing winds, and it must have come from the west after having travelled about thrdu-quarters of the way round the earth. The brilliant sunsets were noticed in South Australia as early as 20th April, and still earlier in South Africa. So far as can be judged, the effects appear to have been more marked to the west and south than over the North Island of New Zealand.

“Again, one writer has suggested that the sky should be more blue than is normally the ease, but this is not so. The effect of the dust is very similar to that of fine smoke, high in the atmosphere. The sun and moon appear hazy, especially when at low altitudes, and' the sky has a milky appearance. As the sun’ is setting the ash can be seen above it, the variations in density being shown by regular waves of irregular streaks of a pearly hue. Then the pink colour after sunset is an effect of diffraction or scattering. This light of short wave-length towards the violet end of the spectrum is scattered most freely by the atmosphere, and is therefore able to penetrate a shorter distance at sunset than that of longer wavelength at the red end. The red is, therefore, the last colour to linger. It is reflected from the ash, which is higher than clouds usually are. The afterglow, therefore, lasts longer than usual, and the brilliance of its appearance is enhanced bv contrast with the darker background of the sky. “The cold is not caused by the absorption of the infra-red heat-rays from the sun, which do not constitiuo a large portion of the energy emitted, but is due to the reflection of the shorter waves back through space. A larger portion of these rays would normally reach the earth’s surtaco' where they arc absorbed and converted into heat' energy. The human body also absorbs these rays, and is 'vanned bv them in a similar way. Ihe heat of the earth is radiated out in long waves, which the particles of dust are too small to reflect back, and which consequently escape. As regards the effect on temperature, according to past experience, there is no reason lor expecting much colder conditions than were endured, for instance, m LW). 'the weather that year was unpleasantly cold, but no very serious effects resulted.” -Ringworm and scalp diseases effectivc,v overcome by using Brices Seboria Soap. 2/-.— Nccs, Ltd., Chemists, Hardy si reel - For nerfeci, results use Rachel Vanishing Cream, which leaves skin smooth and dewy. ' l/6 jar.—Buxton, Ltd.