Roadside Geology: Wupatki and Sunset Crater Volcano National Monuments | AZGS Document Repository
Sunset Crater is a cinder cone located north of Flagstaff in U.S. State of Arizona. The crater is The date of the eruptions that formed the meter-high cone ( 1, ft) was initially derived from tree-ring dates, While the volcano is considered extinct, despite its young geologic age, the San Francisco volcanic field is still. Sunset Crater is in the eastern part of the San Francisco volcanic field. Smiley, T.L., , The geology and dating of Sunset Crater, Flagstaff, Arizona: New. Dating the Eruption of Sunset Crater, Arizona - Volume 2 Issue 1 - John C. McGregor. the following methods: geology and paleontology, distribution, typology, . Museum of Northern Arizona, Flagstaff, Arizona, May,
Geological Survey in Menlo Park. Samples were analyzed on a spinner magnetometer and taken through a step-wise alternating frequency demagnetization process to separate out, and discount, any postemplacement magnetization.
Location of paleomagnetic samples collected in Note that sample BN2A was collected inand is shown here because the sample location was relocated and plotted during the collecting session. Sunset Crater paleomagnetic samples collected in The mean magnetization of each site was also converted to a virtual geomagnetic pole.
Interpretation of paleomagnetic results requires an awareness of probabilities at all times. The error ellipses illustrated in Figure 2 include the area in which there is a 95 percent probability that the real virtual geomagnetic pole is somewhere within the ellipse.
The highest probability for the real location is at the cross in the center of the circle. The sample and site errors derive from geologic variability, sampling errors, and analytical errors. Analysis of more samples tends to reduce these errors. In this case, however, the errors are fairly small, and likely would not improve much with further sampling. Southwest archaeomagnetic master curve SWCV with the virtual geomagnetic poles for the three groups of Sunset Crater lavas plotted on it.
The circles indicate the area in which there is a 95 percent probability of the real location of the virtual geomagnetic pole. Tick marks indicate year intervals and some are marked with the year [A.
Paleomagnetic data from Sunset Crater samples collected in and Year Site Number Lat. Other sites were sampled by Champion during the mids. The two sites shown in brackets were excluded from the statistical analysis for the eruptive unit Bonito lava flow. Page 11 A Paleomagnetic Dating Study of Sunset Crater Volcano Page 12 which the ellipses are plotted also has a certain amount of error associated with it.
Roadside Geology: Wupatki and Sunset Crater Volcano National Monuments
These errors include paleomagnetic sampling and analysis errors, as well as errors in accuracy or lack of precision in the independent dating of the features and sites. The paleomagnetic data allow an interpretation that the Sunset Crater lavas were extruded between approximately A.
This long period is allowed because the secular variation curve loops back upon itself in the relevant time period. Therefore, the early lavas could not have been erupted prior to A.
Dates are currently somewhat problematic, as the next 50 years shows little secular variation. A small difference in the error ellipse can represent 50 years difference in time.
Conversely, the South East Fissure ellipse, taken alone, allows a date as late as about A. The Bonito error ellipse allows a date of A.
Sunset Crater - Wikipedia
Periods of less than 25 years cannot be resolved from these data; however, based on modern cinder cone volcanoes, that would be within the range of length of eruption as would a much shorter eruption. Eight cinder units were identified by Amosand he found no evidence for erosion between the emplacement of each. He calculated an emplacement period of hours for each unit geologically instantaneously.
However, Amos also argued that some period of time passed between the emplacement of each unit, because the wind directions and, in some cases, the vent location, shifted.
The lack of erosion between units seems to argue that not much time elapsed between depositional events, as some evidence of eolian erosion would be expected if time was a factor. In a denuded area, fine lapilli mm diameter move easily and form dunes. With no evidence of dunes forming between tephra layers, a short time period for deposition of the scoria blanket is required—on the scale of a year or two at most.
If this is accepted, the eruption would need to have occurred in the area where the error ellipses for all three groups intersect—approximately A.
However, because this is during a period when secular variation was slow, and thus age control is poor, the eruption may have been as late as A. This is followed by extrusion of lava flows, with or without continued scoria fall, for a period of days to a few years.
The paleomagnetic data are consistent with such an eruption sequence, but do not prove it occurred. The data can also allow an eruption that spanned the period from A.
Conservatively, we interpret the paleomagnetic and geologic evidence together to indicate the eruption occurred over a period of a few years sometime between A. Evidence for a Large Magnitude Strombolian Eruption. Implications for the Global Geomagnetic Field. Open File Report No. Museum Notes 5 4: Museum of Northern Arizona, Flagstaff. Southwestern Journal of Anthropology 1: Museum of Northern Arizona Bulletin No. A Critical Review of Flagstaff Archaeology, University Microfilms International, Ann Arbor.
Final Report, compiled by B. References Cited Page 16 Ferguson, T. Hopi History, Culture, and Landscape. Geological Society of America, Boulder. Eighmy Revision to the U. The cone is about 1, feet m high and 1 mile 1. The main crater at the summit is feet m in diameter. The eruption at Sunset Crater covered and area of square miles 2, square kilometers with lapilli and ash. The eruption was Strombolian in style and large, with eruption columns as high as several hundred feet meters.Sunset Crater Volcano National Monument
The tephra covers parts on the Bonito and Kana-a lava flows which were erupted from Sunset Crater. The Bonito lava flow erupted from the west and northwest base of the cone and covered an area of 1. The Kana-a lava flow was erupted from the base of the east side of the cone and traveled 6 miles 9. Aerial view of Sunset Crater. Photography courtesy of National Park Service.
- Sunset Crater
The Sunset eruption is unusual because the volume of volcanic products about 0. The Sunset event had a severe effect on the Sinagua Indians that lived in the area, forcing them to temporarily leave. Inside the main crater of Sunset Crater. In the s, H. Colton saved the cone from severe damage by averting the attempt of a Hollywood movie company to blow it up in order to simulate an eruption. This led to the establishment of the Sunset Crater National Monument. Geological Survey for providing photographs.