SUNSET CRATER

Sunset Crater National Monument offers a comprehensive study of area which was at one time the scene of volcanic action and which today carries the mark of eruption.

Sunset Crater, a grim reminder of the cataclysmic forces of nature, reveals a story that is without parallel in the nation. To the casual visitor it is merely an exceptionally well preserved volcano. Yet underneath the ash lie the remains of prehistoric Indian homes destroyed by the eruption. On top of the black cinders, for miles around are abandoned rooms, mute evidence of the only prehistoric Indian land rush to be created by a volcano. Destructive and yet beneficial to ancient man, it was through this association that it was possible to date the eruption as having taken place between 1046 and 1071, A.D.

Approaching Sunset Crater National Monument along US Highway 89 just north of Flagstaff, one's first view is of a steep sided cinder cone, the rim of which glows even on a cloudy day as though it were bathed in the last rays of the setting sun. It was Major J. W. Powell, of the U. S. Geological Survey, who first expressed this phenomenum by naming the volcano Sunset Crater. It is only this fact which distinguishes it at a distance from the neighboring volcanoes, many of which are larger.

Upon leaving the highway, one enters a pine forest and it is here that the volcanic cinder first became noticeable-a fine black sand. The closer one approaches the crater the deeper the cinder gets and the more sparse becomes the vegetation. Just around the last of the low cinder hills the lava flows come into view, lava so fresh looking that it is difficult to believe that it is 900 years old. Penetrating further into this scene of vast desolation on the road over the rough lava one has the feeling of being transported into another world. Frozen pools of lava, spatter cones, an ice cave and curious squeeze-ups surround the cone which rises 1000 feet above its base.

While this is the most recent activity in the San Francisco volcanic field, it is by no means the only eruption, just the latest, and a rather puny one at that, of a long series of more than four hundred eruptions which have taken place here during the last million years or so.

Underlying the earth's crust, sometimes no more than 12 miles down, is a huge reservoir of magma (lava) which, due to the pressure of overlying materials, is trapped. Here in the Flagstaff region, as in many other parts of the world, there have been movements of the earth's crust and at intervals this magma has been able to escape to the surface. Sometimes it takes the form of fissure flows where no cones are built. The lava flows out from a crack in the earth and, in this locality, has traveled as much as 20 miles. This is the type of volcanism which preceded all the volcanoes you see here today. Fine examples can be viewed at Wupatki National Monument.

The second period of activity seems to have been characterized by "quiet eruptions." The word is rather an understatement since these eruptions were really violent and produced some of the largest volcanoes known. What is meant by the term is that magma containing a relatively small amount of gas welled up in a central vent, building up into a cone of lava. The nearby San Francisco Peaks are a good example of this type eruption; at one time they were apparently 3000 feet higher than at present. An idea of the relative age of the Peaks is given in the fact that it was extinct at the time of the glacial period, and there is evidence of mountain glaciers in the inner basin.

Finally came the third period of activity, the one to which Sunset Crater belongs. Sunset Crater is the result of a typical "violent" eruption. The magma contained a great deal of gaseous material and upon being released through the vents was blown into bits and solidified into bombs, small stones (lapilli), and the fine cinders which, incidentally, are not at all related to the cinders we take from our stoves. This kind of eruption, the violent type, has been rather cleverly compared to a warm beer bottle foaming, and the quiet type to molasses oozing out under low pressure. Basically this is true although there are fireworks with each type.

That Sunset Crater was the result of a relatively minor eruption is shown by the estimate that the San Francisco Peaks produced 38 cubic miles of material, compared to 1 per cent of that from Sunset. Yet it is interesting to note that to haul away all the material ejected from Sunset would require a freight train at least 163,000 miles long.

A quite accurate reconstruction of the course of events during the eruption of Sunset Crater is possible. Between the years 1046 and 1071 A.D., a fissure about four miles long, which can still be traced today, opened up. At one point the breach was wide enough or, one might say, weak enough, that thousands of tons of molten lava shot up into the air. Containing a great deal of gaseous material, the lava was shattered into fragments, some large, some small. The heavier materials dropped around the vent while the lighter material was carried away by the prevailing southwesterly winds and covered a vast area toward the Painted Desert.At the same time the lava flows seem to have come from near the base of the crater. There are two distinct periods of flow; one which took place during the cinder fall, and is consequently buried under the ash which is reddish in color due to chemical action. The other is the very prominent flows which took place after the cinder fall had ceased and are consequently completely exposed and very fresh in appearance. There are also two separate lava flows. Bonito Flow, the one seen by all visitors, poured into an intercone basin and was thus dammed. Kana-a Flow, to the east of the crater, is less distinct but is visible along the cinder road to Wupatki National Monument.

Sunset Crater was set aside as a National Monument in 1930 as a result of the efforts of the Museum of Northern Arizona after a movie company attempted to dynamite the slope of the crater during the filming of a movie. It can easily be approached from US Highway 89 at a point six miles north of the junction with US 66. No personnel is stationed at the monument but trailside signs mark the points of interest.