Just across the border to the north of the Grand Canyon is the State of Utah. The SW part of the state has five basaltic volcanic fields that were active fairly recently. These include the Hurricane, Bald Knoll, Kolob, Santa Clara, Markagunt Plateau, and Black Rock Desert volcanic fields. All of these fields have been recently active in the last 4 Ma. The most recent activity is at the Black Rock Desert field which hosts the state’s youngest rhyolite dome and youngest lava flow.
The region is generally considered a high desert. It is sparsely populated and gets sporadic rains. The lack of precipitation made it difficult to date lava flows and cinder cones, as older activity looks new and pristine. Things that are today known to be 30,000 – 50,000 years old were initially dated as less than 1,000 years old. Modern dating technology has corrected earlier estimates in recent years.
In the not so distant past, Great Salt Lake next to Utah’s capital, Salt Lake City and neighboring Provo, was much larger. Today, it covers over 4,400 km2. 14,000 years ago, it was much larger, covering much of the western part of the state. This larger body of water was called Lake Bonneville, covering some 51,300 km2 of today’s desert at its largest. It was also much deeper at 300 m in its deepest point compared with Great Salt Lake at 10 m today. At least two of the volcanoes in the Black Rock Desert erupted through Lake Bonneville. Erupting through a lake that lake did not exist until 32,000 years ago makes dating the two volcanoes much easier..
Lake Bonneville was filled with melt water from the Canadian ice sheets. Around 14,500 years ago, it emptied catastrophically through a natural dam near Red Rock Pass, Idaho, washing away the dam in what is now called the Bonneville Flood. The lake level fell around 100m over the course of a year or so, draining around 4,200 km3 of water to the west.
The a portion of the dry lake bed under the former lake is called the Bonneville Salt Flats, and is currently a location testing and racing high speed land vehicles. The world record for the fastest land speed record was set in 1997 on a salt flat in Black Rock Desert, south of the Bonneville Salt Flats. It was just under 1,228 km/hr, which broke the speed of sound at that altitude and temperature.
Terrain in western and southwestern Utah is spectacular and has been preserved in a number of National Parks, National Monuments, and state parks. There is also a significant military presence with a variety of gunnery ranges and military installations in western Utah.
Western settlement of Utah took place starting in 1847 when Brigham Young brought his family and over 140 men into Utah and started the Mormon migration into Utah and Nevada. Native tribes in Utah include the Ute, Paiutes, Goshutes, Shoshone, and Navaho.
Bald Knoll Volcanic Field
Bald Knoll is the youngest of a group of basaltic cinder cones on Paunsaugunt Plateau in southern Utah. There are another pair of cinder cones – Buck Knoll and Black Knoll. It is some 100 m high and topped with a summit crater 280 m in diameter. It produced a lava flow that covers 13 km2. Flow thickness is 12 m where exposed. It may be 2 -3 times greater. Total volume is 0.1 – 0.2 km3.
While the Bald Knoll lavas appear to be only a few thousand years old, field evidence suggests it is much older than that. One reason is alluvial sediment that has buried the margins of the lava flow. Another is the extent of erosion along a 3-km stretch of Johnson Canyon. This is an arid region, and Johnson creek is at best intermittent, so stripping the lava flow suggests substantial age.
The Bald Knoll lava is undated. Neighboring lava flows at Virgin Flats and Volcano Knoll date 0.37 and 0.34 ma. Based on its location and nearby erosion, the best guess for the date of the flow is 0.3 Ma.
Kolob Volcanic Field
The Kolob Volcanic Field is located at the border of Zion National Park. It is a chain of basalt cinder cones and lava flows. The youngest are cinder cones in Diamond Valley. These are Spendlove Knoll, Firepit Knoll, and Crater Hill. The highest point in Zion is called Lava Point.
The oldest of 13 lava flows around Zion is 1.4 Ma. The Crater Hill lava flow and cinder cone are estimated at 100,000 years. The Crater Hill flow has columnar joints in places.
Lava flows out of Kolob extend 10 – 15 km down neighboring valleys. They crossed drainages and created a pair of lakes – Coalpit and Grafton. These lava flows date 122,000 years based on sediments in Grafton Lake.
Activity over time generally worked its way from west to east, similar to what we saw in northern Arizona.
Santa Clara Volcanic Field
The Santa Clara volcanic field covers some 1,600 km2 and includes over 50 cinder cones and lava domes. It has been active since around 2.5 Ma. The field erupted in three main episodes: 1.1 – 0.95 Ma; 0.7 – 0.55 Ma; and 0.35 – 0.25 Ma. Initial eruptions took place as early as 2.3 Ma. Most of the eruptions were basaltic, though a pulse of dacite occurred 2.0 Ma and 1.0 Ma ago. The youngest eruptions took place some 27,000 years ago near Snow Canyon State Park. The Santa Clara lava flows start at a pair of what appear to be very new cinder cones, and travel 16 km down Snow Canyon. Although initial estimates of the age of these cinder cones and lava flows were around 1,000 years, they date in the 27,000 year range. https://thenaturalhistorian.com/2013/09/17/nh-notes-inverted-valleys-a-question-of-age/
Basalt eruptions created cinder cones, spatter cones, lava flows, and lava tubes.
Most of the vents are aligned with regional faults of the Basin and Range Province. Some are not.
Snow Canyon State Park is near St. George. It has a 2.4 km trail called Cinder Cone trail which winds around the lava flows and goes up what looks to be one of the most recent scoria cones in the field.
86,000 live within 5 km of the field, and nearly 200,000 within 100 km.
Anasazi lived in the canyon from 200 – 1250. Paiute lived there from 1200 – the mid-1800s.
Volcanic activity generally worked its way from west to east over time.
Hurricane Volcanic Field
The Hurricane volcanic field produced thin aa lava flows and 10 cinder / scoria cones grouped into 10 clusters. The field was active 0.35 – 0.26 Ma. This field straddles the Hurricane fault running north from the Grand Canyon.
One of the interesting things about this field is the variability of the erupted magmas which range from silicic to alkali basalts. There appears to be a variability across the line of discontinuity of the fault over time. There are also some evolved magmas and varying degrees of fractional crystallization.
One of the physical features of this field is caused by the erosion around its lava flows. The flows typically went down valleys. Over time, these valleys were further eroded and left bluffs capped by thin lava flows which are the harder rock, one of which is pictured above.
Markagunt Volcanic Field
The Markagunt Plateau volcanic field marks recent activity in the ancient caldera fields we discussed in a post a year ago. These calderas were active some 38 – 18 Ma and include the Indian Creek – Caliente, and Marysville volcanic fields. Markagunt also has one of the largest landslides ever discovered in the US, the Markagunt gravity slide some 22 Ma. https://volcanohotspot.wordpress.com/2016/10/18/the-utah-nevada-ignimbrite-flareup-of-30-ma/
The name comes from a word meaning “highland of trees” in the Paiute language.
The field is a group of cinder cones and lava vents on the Markagunt Plateau. Initial eruptions began some 5 Ma and appear to be mostly continuous to about 1,000 years ago. Numerous lava flows with the oldest being trachytic, andesitic and rhyolitic lavas. These were followed with at least two spurts of basaltic eruptions out of lines of cinder cones. Some of the lavas blocked drainages which did not reestablish flow across the lava flows.
Markagunt covers some 3,000 km2. Eruptive products are primarily basalt. There are 40 – 50 cinder cones, spatter cones, and lava flows. There were three episodes of eruptions: 5.3 – 2.8 Ma; 1.0 – 0.5 Ma; and less than 0.5 Ma – less than 37,000 years ago. The youngest flows produced blocky flow fronts that are 30 – 60 m tall. It also contains one of the largest lava tubes in the state at Mammoth Cave.
This is a sparsely populated part of Utah, with just under 1,000 living within 10 km of the field.
It is not completely geologically inactive, as a 3.2 magnitude earthquake struck the Markagunt Plateau May 31, 2015 at a depth of 4.0 km. https://earthquake.usgs.gov/earthquakes/eventpage/uu60112622#origin?source=uu&code=uu60112622
Black Rock Desert Volcanic Field
The Black Rock Desert volcanic field is in west-center Utah. It is also part of volcanic activity arising out of the Basin and Range tectonic extension in the western US. It covers some 7,000 km2 and is 145 km long. It has been active for 6 Ma, with the first eruptions being rhyolite domes and a basalt flow some 6.1 Ma. It has been recently active for the last 2.7 Ma. It’s most recent eruptions took place in the central portion of the field some 720 years ago. These eruptions were at Ice Springs. It is considered to be an interplate volcanic field though its original magmas were similar in composition to those out of the Rio Grande Rift.
This field differs from most of the other basalt fields in that it also has andesite, dacite, and rhyolite. Eruptions are mostly monogenetic, though some are more complex. Volcano types include cinder cones, shield volcanoes, domes, maars, lava tubes, and a caldera. There are 30 small volume monogenetic volcanoes.
Black Rock Desert is the youngest volcanic field in Utah. Many (most?) of the vents, cones, and hot springs are aligned with fault lines due to the spreading and uplift of the Basin and Range Province over the last 17 Ma. It contains the youngest rhyolite dome, White Mountain, and the youngest lava flow at Ice Springs. Two major eruptions at Tabernacle Hill and Pavant (also spelled Pahvant) Butte took place initially under Lake Bonneville and formed volcanic islands in the lake.
The field was covered in part by Lake Bonneville during the last ice age some 22,000 – 12,000 years ago. Erosion from the lake removed evidence of older volcanic vent deposits for some eruptions older than 12,000 years.
Magmas appears to be a variation of an olivine tholeiitic magma from 15 – 35 km deep that received small additions of mantle-derived magmas as they move upward. They underwent fractional crystallization and minor contamination over the last million years.
The Black Rock Desert volcanic field is further subdivided into smaller groupings of volcanoes and lava flows. These are also called volcanic fields and include the following:
Cove Fort Volcanic Field
Cove Fort contains several rhyolite lava domes and associated pyroclastic deposits. These date between 0.8 – 0.5 Ma. Basalt and andesite eruptions took place in the valley east of the rhyolite deposits. Pahoehoe flows started 1.3 Ma. Two cinder cones, a shield volcano, and associated lava flows took place between 1.0 – 0.5 Ma. The final eruption included andesite and created a reddish cinder cone with a basalt lava flow extending 20 km SW some 0.3 Ma.
Twin Peaks Volcanic Complex
This represents a rhyolite caldera and associated eruptions. Initial eruptions some 2.7 Ma formed a field of rhyolite lava domes. This was followed by a pyroclastic tuff that produced around 100 m of subsidence over a 120 km2 area. The depression was filled with a lake and sediments, forming a limestone deposit. Eruptions of basalt lava flows and additional rhyolite domes filled the rest of the caldera. This ended with formation of Burnt Mountain cinder cone and associated lava flows 2.1 Ma. Perhaps 12 km3 of material was erupted in this field between 2.7 – less than 1.0 Ma. There were four eruption pulses, the first two silicic, and the last two basaltic.
Beaver Ridge Lava Field
Beaver Ridge eruptions took place around the same time as Cove Fort, 1.5 – 0.4 Ma. The field includes several basalt lava flows and cinder cones that were highly eroded by Lake Bonneville, dacite, and andesite lava domes. The field includes the White Mountain lava dome, formed 0.4 Ma, the youngest rhyolite dome in the state. The andesites and basalts are highly iron-enriched.
The Fumarole Butte field was active sporadically from 6.1 – 0.3 ma. It includes the basalts of North Butte and rhyolite lava domes of the Topaz Mountains. The youngest volcanoes include the 0.9 ma Fumarole Butte shield volcano and the 0.3 ma Smelter Knolls basalt flows and maar.
Ice Springs Lava Field
Ice Springs lava field is the youngest, perhaps as recent as 600 – 900 years ago. Covers 20 km2. 3 large and several smaller craters. Still shows thermal activity. The lava flows came from spatter and cinder cones and are called the newest rock in the state.
Devil’s Kitchen is a lava flow that sounds hollow when travelers crossed it with horses and wagons. It is a lava flow / fault line between Pavant Butte lava field and the Ice Springs lava flows. There is a 20 m scarp along the fault line.
Pavant lavas cover most of the northern half of the Ice Springs Field. Ice Springs lavas cover a smaller portion in the middle with Tabernacle and Beaver Ridge lavas to the south. In the far SE portion of the field we have The Kanosh Field with Black Rock volcano. In the far SW portion of the field we have the Deseret
The Ice Springs volcanic field includes both Tabernacle Hill and Pavant Butte tuff cones.
- Pavant (or Pahvant) field. Initial eruptions were basalts from a vent area in the vicinity of the final cinder cone. Initial eruptions took place before Lake Bonneville formed, no earlier than 0.13 Ma. Pavant Butte is the final cinder cone some 25 km W of Holden. Mainly pahoehoe lava flows around and to the south of cone. Many lava tubes. The Pavant Butte ash was erupted less than 16,000 years ago and is interlaced with barrier-beach lagoon debris. It also erupted underneath Lake Bonneville. There is a wave-cut terrace surrounding most of the tuff cone. Higher portions of the cone have basalts that came into contact with water as they were erupted.
- Tabernacle field. Smallest field, with lava flows covering 20 km2. Includes Tabernacle Hill. Initial eruption was phreatomagmatic and probably below the surface of the lake. It was followed by an effusive phase that included a small lava lake. The cone was eventually breached by the lava flow and part of the cone rafted away. Basaltic flows from the base of Tabernacle Hill, a small tuff cone in the center of the field. A basalt flow from this cone shows pillows, wave-rounded cobbles, and tufa on its outer margins, meaning it was erupted into Lake Bonneville around 14,400 years ago. There is a depression described in one article as a central caldera, though it is difficult to get a full-fledged caldera in a kilometer wide scoria cone. The Meadow Lava Tubes are a tourist destination created by Tabernacle eruptions. The nearby Meadow Hot Springs are three different geothermal pools within half a kilometer of one another.
The Kanosh volcanic field is just SE of the Beaver Creek and Tabernacle lava fields. It has several cones and massive lava flows. Much of it is obscured by Bonneville sediment. The lavas date at 0.67 Ma. The cones are cinder – spatter cones, the largest called Black Rock volcano. Flowing lava breached the horseshoe shaped cone, rafting a segment of it a kilometer westward. The cinder cones are just under 100 m tall. Vents on the field are along a generally N – S line. There are hot springs and a tuff field just to the north of the group of volcanoes and lava flows.
Volcanic fields of SW Utah are driven by the tectonic movement (uplift and rotation?) of the Colorado Plateau to its east, and the continuing extension and uplift of the Basin and Range Province in the western US. In some ways, recent activity is an extension of the intraplate basaltic activity in Northern Arizona discussed a year ago. In other ways, particularly in the vicinity of the Colorado Plateau, initial eruptions echoed the caldera outbreak in Utah and Nevada some 38 – 18 Ma. Some of those magmas remained in magma chambers awaiting the next injection of hot, fresh, unevolved basalts. Initial eruptions from most of these fields appear to be (at least to me) from magma chambers partially destabilized by new magma from deeper. Over time, the initial evolved magmas and eruption products tended to primitive basalts.
There are two recent volcanic belts in SW Utah. They are located in the Basin and Range Province, and the transition zone into the Colorado Plateau, meaning that the activity may be related to the discontinuity between the Colorado Plateau and the rest of the continent.
The youngest is the north – south trending Black Rock – Grand Canyon Belt. It has been active between 2.5 Ma – present. Magmas appear to be related to the ongoing east – west extension of the province. Magma formation for recent eruptions may be caused by decompression melting as much as anything else.
The older belt is the Pahranagat – San Rafael belt, dated between 15 – 3.5 Ma. It has a NE trend in activity over time. The vector is similar to that of Yellowstone. Basalts are more primitive and alkaline over time.
As I mentioned earlier in this section, one of the puzzling things about these volcanic fields is the variable chemical composition of the erupted magmas. Instead of standard intraplate basalts, they initially are more like lavas erupted in the Rio Grande Rift – rhyolites, dacites, and andesites. One suggestion is that the chemical differences may be a characteristic of volcanic activity at or near the margin of the Colorado Plateau. Another suggestion is that the initial magmas were destabilized by ongoing introduction of young, hot, basalts into existing magma chambers. The proportion of basalts erupted has increased over time. Younger basalts are generally less contaminated with melted rock from the crust than the older ones.
The major geologic structure in the region, the Hurricane fault is thought to be the boundary between the Colorado Plateau and the Basin and Range Province to its west.
These relatively small volcanic fields generally mark the outlines of the SW corner of the Colorado Plateau. Basalts appear to reach the surface via lines of weakness formed by Basin and Range extension and uplift. They also appear to find their way to the surface via the line of weakness between the Colorado Plateau and Basin and Range Province as the plateau rotates a bit.
The region is still a healthy producer of geothermal energy and has potential for future geothermal energy production.
The Black Rock Desert field is the most recent and appears to be the most active. I would not be surprised to see additional eruptions out of this part of the state in the not so distant future. Should these eruptions take place, they should be mostly basaltic in nature, though we can always be surprised.