1 Library Research – Works Cited Page

- APA style; relevant content; college-level sources; websites not allowed – sources must be articles, books, or documents.

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Site Visit - Field Observations Form - hand written in field, fully completed. /10 - Photos - 6 of your own photos, 2 per page, descriptive photo captions in complete sentences, photos are original and show relevant geologic features. Photos copied from the internet will result in a grade of zero for the assignment.

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- Map – Your own final hand-drawn map of the site showing geologic features, includes title, north arrow, scale bar, legend of all map elements; use color, show location of photos, show location of relevant geologic features and label them, show human features like roads and trails. This has to be a neat hand drawn map of the park.

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Final Report - Three-page research paper - Content - Relevant observations and explanations of geologic features, good relationship between your observations and the results of your library research. Scientifically relevant physical geologic features. Show relationship between geologic features to your observations.

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- Writing style - Research report style that is objective, cites references, and is concise, direct, organized, and structured. Will be free of grammatical and spelling errors. Topic sentences for each paragraph, all sentences in paragraphs relate to main point of paragraph.

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- In-Text Citations: Followed in-text citation procedures for APA correctly. /10 Total Points /100

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Table Mountain Utah:

A Not So Old Basalt Lava Flow Alone in the Utah Desert

Zach Skrede

Geology 1010-004 Spring 2015

30 April 2015

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Abstract

The basalt flows in the northern region of Utah are all similar in composition and age;

however they are all unique and unrelated. The basalt at Table Mountain is perhaps one of the

more pure and distinct examples of olivine and plagioclase basalts in the region. The aphanitic

nature of the rocks indicates that this mountain was formed in a very hot, low pressure

environment. Table Mountain was also formed in two separate events with a layer of pyroclastic

tuff in between the different layers; this tuff can also be found embedded in-between large

sections of weather rock from the first flow.

Basalt lava flows have occurred in the Northern Utah desert and Southern Idaho. One

such flow is the Table Mountain formation just west of the abandoned town of Kelton, UT. This

formation has a very distinct shape, rock composition and history that is unique among the

surrounding area. Among the processes that created this formation, the age, rocks present and

significance will be investigated.

Table Mountain was formed during the Pliocene and Miocene period (Utah Geological

Survey, 5) or around 3.2 and 9.6 million years ago and is the product of two separate, unrelated

eruptions. Evidence of the two eruptions can be seen through the existence of two similar sets of

rocks with formations of pyroclastic tuff filling in gaps of the older flow. The mountain is

somewhat oval in shape and rises approximately 250 feet above the surrounding terrain. The

original vent appears to rise straight up with large columnar boulders that have weathered off

surrounding the perimeter of the mountain.

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Because of the relatively small size and isolated location of this basaltic plateau it could

be concluded that the flow originated from a small, singular vent as opposed to a long fissure that

would have created a longer and shorter feature in the end (Mahoney, 496). The presence of

very small Olivine crystals in the basalt indicates that the magma erupting from this vent cooled

very rapidly. The confined and orderly structure of the mountain also signifies that the eruption

was not explosive in nature, rather a smooth steady flow of magma.

The rock composition is almost entirely of aphanitic olivine based basalt, a dark gray

very fine grained igneous rock with plagioclase feldspar and large amounts of iron. The high

iron content is signified by the oxidized appearance and when large flat sections of the rock are

struck a unique metallic tone is generated. (Wang, 18). The outer surface of the rocks has been

weathered and oxidized to an extent that the olivine crystals are not visible unless a specimen is

broken open. The grain size and cleavage is imperceptible without the use of microscopic

viewing equipment however prior studies of this particular basalt has revealed subhedral

phenocrysts with a size around 0.6mm (Wang, 28). Amongst the olivine crystals the next most

dominant mineral is plagioclase feldspar with stumpy crystals ranging in size from 0.02 mm to

0.4 mm in length and 0.7 mm to 1.0 mm in diameter.

The occurrence of plagioclase and olivine with the absence of clinopyroxene suggests

that pressures were not great enough to form pyroxenes although temperatures certainly were

high enough according to Bowen’s reaction series. This indicates that the flow originated from

relatively low depths, less than 15 km below the surface (Wang, 67).

The pyroclastic tuff that is present is of different composition than the basalt and is not

incorporated into the larger formation. The tuff has higher levels of crustal material

contamination, materials such as silicon dioxide and magnesium oxide, indicating that it was not

5 melted into the basalt flow, but rather pushed up and spread about as the magma approached the

surface. Because Table Mountain is comprised of two separate flows a layer of tuff can be found

in between the two flows and provides a distinct delineation between the events. The tuff is

comprised of mostly sedimentary strata and is loosely formed with large pores. The pattern in

which it is distributed amongst the basalt suggests again that it was not fully melted and was able

to survive the eruption.

Weathering of the mountain has been constantly taking place and is certainly visible

today. One of the most striking features of Table Mountain are the massive boulders that have

been shed from the faces over the years through the power of water penetrating small cracks and

freezing. These boulders range in size from approximately three feet in diameter all the way up

to twenty feet. The south facing slope is a maze of these boulders with large gaps and crevasses.

There is a very thin layer of sedimentary strata on top of the feature, deposited primarily by wind

and due to the unrelenting nature of the elements in this area it is unlikely the layer will ever

become much thicker than it is.

There is no real monetarily viable use of the mountain so it remains largely unmolested

by human activity. The primary uses of Table Mountain remain recreational passer-bys looking

for a photographic viewpoint of the area and as an attraction for geology students to study and

write reports about. I have found Table Mountain to be a very unique and fascinating feature

alone in our Utah desert.

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Works Cited

Kerr, S.B., (1987). Petrology of Pliocene (?) basalts of Curlew Valley (Box Elder County) Utah: Logan, Utah State University, M.S. thesis, 84 p.

Mahoney, John J. (1997) Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism. American Geophysical Union

Utah Geological Survey. (2012). PROGRESS REPORT GEOLOGIC MAP OF THE GROUSE CREEK 30' x 60' QUADRANGLE AND UTAH PART OF THE JACKPOT 30' x 60' QUADRANGLE, BOX ELDER COUNTY, UTAH, AND CASSIA COUNTY, IDAHO. (Utah Geological Survey Report # 598). Salt Lake City, UT Voit, R.L., (1985). Petrology and mineralogy of Tertiary volcanic rocks west and southwest of Kelton, Box Elder County, Utah: Logan, Utah State University, M.S. thesis, 90 p. Wang, Yunshuen, (1985)."Petrology ot Tertiary (?) Volcanic Rocks of Snowville Area, Utah, and Tertiary-Quaternary (?) Volcanic Rocks of Table Mountain and Holbrook Areas, Idaho" (1985). All Graduate Theses and Dissertations. Paper 3830.

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Table Mountain, Kelton, UT

Olivine and Plagioclase Basalt

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Pyroclastic Tuff between layers of Basalt

Thin Sedimentary Layer on Top and Geologist in Training

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Large Boulder Field on South Face

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Weathering Face

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