The American Cyclopædia (1879)/Hecla

HECLA, or Hekla, a volcanic mountain of Iceland, situated in the southwestern part of the island, in the district of Rangarvalla, 40 m. from the coast. Hecla rises to the height of 5,104 ft., to the eastward of a large and comparatively fertile plain intersected by the rivers Hvita and Thjorsa. Its approach is over vast lava beds lying irregularly one above the other. The peak or cone itself surmounts a long palagonite ridge 2,000 ft. high, running N. E. and S. W., and forming in reality a single volcanic fissure along which the points of eruption are continually changing. It is the middle one of five main ridges composing the Hecla system, all dominated by the conical crest of the volcano. This is built up with scoriæ, slag, and ashes, kept together by the streams of lava. Though above the snow limit (in Iceland from 2,000 to 2,500 ft. above the sea), it is not entirely covered with snow in summer. Down the western side slopes a snow fond of considerable dimensions. The top of the mountain is nearly flat, forming a broad table a quarter of a mile long by 50 rods across. The ground feels warm; on digging to the depth of six inches smoke bursts forth, and smoking heaps of lava are scattered over the surface. There are five craters on the peak, four of them on its side. The highest, on the summit, has been quiescent for ages. It is an irregular chasm about a quarter of a mile long, 300 ft. wide, and 250 ft. deep. The bottom is covered with volcanic sand, moist earth, and in some places with snow; but from many fissures on its sides issue smoke and hot steam. The recent craters are filled with black smoke, red scoriæ, and sulphur.

Of the 86 volcanic outbursts to which Iceland has been subjected since 874, Hecla has contributed 39, Katla 13, and the submarine volcano off Cape Reykjanes 12. The longest period of Hecla's inactivity has been 79 years, and the shortest 6; but the violence of the eruption bears no proportion to the preceding period of rest. The first recorded outbreak of Hecla occurred in 1004, the last in 1845. The most disastrous began on April 6, 1766, when enormous columns of ashes were discharged, accompanied with thunder and lightning, and in the space of two hours destroyed five farm houses in the valley of Kangadalr; scoriæ of two feet in circumference were hurled two miles, large extents of birch copse were buried, and the pastures almost utterly ruined; thick masses of slag and scoriæ covered the surface of the distant Thjorsa and dammed up the Ranga river, causing the lowlands to be inundated; and the prodigious quantities of loose volcanic matter which these rivers bore down to the sea hindered the progress of the fishing boats, and covered the southern coast for 20 miles, in some places to a depth of two feet. At noon of the first day a strong southerly wind carried these ashes toward the northern districts, turning the daylight into pitchy darkness, while deafening reports reverberated over the island. On April 9 a stream of lava poured down toward the southwest, issuing from two craters, one on the summit, and another toward the southwest. On the 21st the column of ashes from the main craters rose to a height of 17,000 ft. Continuous and disastrous shocks of earthquake accompanied the eruption. Epidemics raged among human beings and cattle; and great quantities of snow fell, accompanied by storms from the northwest, which lasted a week. The eruption of 1845 was preceded by unusual atmospheric conditions. The snow patches on Hecla's ridge had diminished in a marked way during the summer; the hot springs to the southeast of the mountain had increased in numbers and activity. On the morning of Sept. 2 dull detonations were heard, and a slight vibration of the earth was perceptible, the summit of Hecla remaining shrouded in black clouds, which about noon spread over the whole sky, discharging a thick rain of yellowish gray, slaggy pieces. At noon it was dark as in the deepest winter night; then a dark, shining volcanic sand began to fall, lasting until noon on the 3d. Sounds as of cannonading were Heard at a great distance, and terrific crashes in the vicinity, which were succeeded by regular detonations, and then a violent rumbling noise. Exhalations, brightly illumined by the glowing mass in the crater, canopied the ridge, as if a steadily increasing sheet of flame shot out from the summit, amid which glowing masses of stone were continually hurled up and down. At nightfall on the 2d a lava stream issued from the N. W. side of Hecla; the watercourses to the west were suddenly swollen by the melted

snows, and carried down vast quantities of mud, earth, and stone. Ships in the neighborhood of the Faroes, the Shetlands, and the Orkneys were overtaken on the 2d and 3d by a shower of ashes coming from the northwest. The flow of lava continued with slight intermissions till April 5, and on the following day the last column of ashes was discharged. As the lava only covered the track of former eruptions, no dwellings were destroyed. Sheep and cattle suffered severely from want of grass. The lava stream poured forth in 1845-'6 is 9 m. long, 2 m. broad in some places, and from 50 to 100 ft. high.