Anosma or 'squeeze-ups'

Colton, Harold; Park, Charles

The Sunset Crater Lava flow lies 15 miles NE of Flagstaff, AZ, and presents the most recent evidences of volcanic action in the San Francisco Mountain area. The surface of the flow bears curious fissures. These fissures are filled with basaltic masses which have been given the name of anosma or 'squeeze-ups.' The Sunset Lava flow, called by Robinson, 1913, the Bonito flow, seems to arise from a fissure at the northwest base of Sunset Crater. From the point of origin now marked by a line of fumeroles, the basalt flowed west and north spreading fanlike over an intercone basin, a basin in which the natural drainage has been blocked by cinder cones. That the flow had two phases is very evident. During the primary phase the flow extended about a mile from the vent. Following this flow an ash fall covered the surface. From the fringes of the primary flow a series of secondary flows poured out into the basin. These flows were probably contemporaneous, as they have coalesced to from an apron in some places a few hundred feet wide and in others almost a mile. The scoriaceous surfaces of the secondary flows are free from volcanic ash. We can, therefore, conclude that an ash fall occurred in the interval of time between the primary and the secondary flows. The primary lava flow is cut by a fissure. This fissure extends from near the base of Sunset Crater a mile and a quarter NW to the edge of the primary flow and varies in width from a few feet to 75 feet. Through this fissure basalt in a plastic condition has been squeezed. The sides of this basalt tongue are grooved, conforming to the walls of the fissure, and slickenside surfaces are usually present. In the wider parts of this fissure, the more plastic inner layers of the mass seem to have slid over the outer less plastic plates so that we find a series of vertical layers pushed into the air. Besides the long squeeze-up, mentioned above, others are known, many of them less than 200 feet long, and one is over 120 wide. All these squeeze-ups are located on or near the edge of the primary lava flow and form points of origin of secondary flows. One fissure but 2 feet wide contains a squeeze-up the top of which does not reach the surface. If we trace the big squeeze-up to its northwest end we are led to a tumbled mass of lava where squeeze-ups radiate in all directions. This wild weird place, which we have called the 'Mother of Squeeze-Ups,' forms the source of one of the larger peripheral secondary lava flows. Here, the scoriaceous lava can be seen to have oozed out of the crack between the squeeze-up and the primary flow. The remains of numerous fumeroles dot the surface of the primary flow but are absent on the surface of the secondary flows. Silicious deposits and the oxidation of the iron in the basalt on thc surface of the primary flow tell of thc action of hot gases. These observations indicate that the lava beneath the primary flow was long in cooling. The squeeze-ups, therefore, seem to have some relation to a deep mass of basalt slowly cooling but still connected with the active vent. Dr. T. A. Jaggar, of the Hawaiian Volcano Observatory, in a letter, suggests that this condition may be similar to 'Schollendomes' in Hawaii. He states that often a lava flat is swollen up at the front of a flow. Lifting the shell is easier than pushing it out. The paste inside breaks through the roof of the dome so formed. The inside is much like a laccolith. In Hawaii, however, the lava is never stiff enough to stand up in arches. Except at the edge of the primary Sunset lava flow the lava seems to be in hydrostatic equilibrium. In other words the average height of the squeeze-up plates are lower than the surface of the primary flow, although individual thin plates may extend 10 feet or more into the air over the level of the flow.Anosma or squeeze-ups seem to be unique. Good examples are abundant on the primary lava flow from the NW base of Sunset Crater.

Anosma or 'squeeze-ups'

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