THE ORDINARY WORK OF THE VOLCANOES.
For most of the time the activity of the volcanoes is rather com monplace. There is a daily routine of work much like respira tion and assimilation in the human body, partly illustrative of a kind of life and partly a preparation for eruptions. The most prominent feature is the presence of lakes of liquid lava, which emit heat and vapors and throw up jets. The surfaces are crusted over and the congealed laver breaks up into irregular blocks which sink and disappear. Fumes of sulphur and aqueous vapors arise from the caldrons, causing visitors to avoid their leeward sides. What may be termed smoke mixed with the vapors will develop clouds overhead or rise in columns spreading out likc the branches of trees or an opened umbrella. Many instances have been cited of the presence of these clouds over Mokuaweo weo, some of them being charged with fine cindery particles and others not to be distinguished from cumulus clouds formed by the precipitation of vapors in a colder region. The tree is evidently an attenuated variety of the copious discharges in times of great activity.
The ebullition is constant. Certain portions in their efforts to rise as bubbles do projectile work, accompanied by noises. The jets spout upwards as much as thirty feet and the action is rythmical. Some speak of these jets as dancing joyously with many variations of height and position. The spiracles are where the melted matter solidifies drop by drop as it is thrown up. The jets are more numerous along the borders because the heat es capes more quickly in the center and thus is cooler.
The Pele's hair, where the flying drops are pulled out into long threads is another instance of projectile action. The knotted parts may inclose crystals.
There seems to be a constant supply of the igneous material, so that the lakes overflow. At first the cooling of the overflow builds up a dome or column. Then the streams flow like rivers all over the floor, perhaps cascading, till the pit is filled up, and then meandering into all the low spaces. Since 1823 the cone of Hale maumau has been built up as much as six hundred feet. The
vapors are mostly steam, sulphurous acid, a little carbonic acid, hydrogen and atmospheric air.
The source of the water has been referred to rain, the ocean and the original magma of the interior. The rainfall in the .eastern part of Hawaii is excessive, reaching to two hundred inches a year at Hilo, and it is rarely the case that visitors fail to receive a good drenching. Because the volcanoes are insular the ocean is not far away ; and it is believed commonly that the seawater gains access to the interior fires for the eruptions, if not for the constant requisite supply. In Vesuvius the entrance of seawater with its dissolved sodium chloride may explain the presence of so much sal-ammoniac and copper chloride among its minerals. Traces of them have been reported for Kilauea, but I have never been able to find any material token of their presence. Hydrochloric acid is so pungent that it could not fail to be de tected, if present. Possibly the bright red saffron and orange spots among the lavas may have been produced by the conversion of iron chlorid into ferric oxide ; but if there is iron chlorid in the lava brought from the ocean, why should not the other chlorids be present ? Vesiculation is justly appealed to as evidence of the presence of water or steam. Professor Dana has fully discussed the matter. He describes five styles of it.
i. The ordinary lava stream of the floor, where the vesicles are oblong and constitute from one to fifty or sixty per cent. of the rock.
2. The common spherically vesiculated lava where the bubbles are too small to be elongated by the flow and constitute from thirty to sixty per cent. of the mass. Such lava is common upon the flows of 188o from Mauna Loa near Hilo. It may not extend downwards more than twelve feet.
3. Glassy scoria in various parts of Kilauea, the scum of the lava, which is often troublesome because one breaks through it in walking. It is easily fusible and the vesicles constitute sixty-five to seventy-five per cent. of the mass.