Geology

Houston’s long history of flooding

Houston, Texas, seat of Harris County, has a long history of flooding because the city was built on a flood plain. The deluge generated by hurricane Harvey in August, 2017, is only the latest episode.

Houston lies within a coastal plain about 50 miles northwest of Galveston. The area has very flat topography which is cut by four major bayous that pass through the city: Buffalo Bayou, which runs into downtown and the Houston Ship Channel; and three of its tributaries: Brays Bayou, which runs along the Texas Medical Center; White Oak Bayou, which runs through the Heights and near the northwest area; and Sims Bayou, which runs through the south of Houston and downtown Houston. The ship channel goes past Galveston and into the Gulf of Mexico.

The land around Houston consists of sand, silt, and clay deposited by local rivers.

The sedimentary layers underneath Houston ultimately extend down some 60,000 feet, with the oldest beds deposited during the Cretaceous. Between 30,000 feet and 40,000 feet below the surface is a layer of salt, the primary source of salt domes which dot the metropolitan area. Since salt is more buoyant than other sediments, it rises to the surface, creating domes and anticlines and causing subsidence due to its removal from its original strata. These structures manage to capture oil and gas as it percolates through the subsurface. [source]

Groundwater pumping also causes subsidence in parts of the city. (See: Geologists find parts of Northwest Houston, Texas sinking rapidly )

Hurricane damage in Houston:

As described by the Harris County Flood Control District (HCFCD) [link]:

When the Allen brothers founded Houston in 1836, they established the town at the confluence of Buffalo and White Oak Bayous. Shortly thereafter, every structure in the new settlement flooded. Early settlers documented that after heavy rains, their wagon trips west through the prairie involved days of walking through knee-deep water. Harris County suffered through 16 major floods from 1836 to 1936, some of which crested at more than 40 feet, turning downtown Houston streets into raging rivers.

Houston was flooded during the September, 1900, hurricane which wiped out Galveston.

In December of 1935 a massive flood occurred in the downtown Houston as the water level height measured at Buffalo Bayou in Houston topped out at 54.4 feet which was higher than Harvey. There have been 30 major floods in the Houston area since 1937 when the flood control district was established in spite of construction of flood control measures.

In June, 2001, Harris County suffered widespread flooding due to hurricane Allison. According to HCFCD, before leaving the area, Allison would dump as much as 80 percent of the area’s average annual rainfall over much of Harris County, simultaneously affecting more than 2 million people. When the rains finally eased, Allison had left Harris County, Texas, with 22 fatalities, 95,000 damaged automobiles and trucks, 73,000 damaged residences, 30,000 stranded residents in shelters, and over $5 billion in property damage in its wake.

Some climate alarmists are claiming that global warming has played a part in the flooding produced by hurricane Harvey. Dr. Roy Spencer debunks that notion here and here. Storms of or greater than Harvey’s magnitude have happened before. Storm damage is not due entirely to weather. Some is due to local infrastructure.

It all boils down to the luck of the draw: if you choose to inhabit a flood plain, you will get wet from time to time.

P.S. Prior to Harvey, which made landfall as a Category 4 storm, the U.S. had gone a remarkable 12 years without being hit by a hurricane of Category 3 strength or stronger. Since 1970 the U.S. has only seen four hurricanes of Category 4 or 5 strength. In the previous 47 years, the country was struck by 14 such storms.

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Eldred Wilson’s Proterozoic Mazatzal Revolution Arizona

The Arizona Geological Survey has just made available for download papers by Eldred Wilson, a pioneer of Arizona geology.

Eldred Dewey Wilson & the Proterozoic ‘Mazatzal Revolution’

Study area map of Wilson (1937)

In 1937, geologist Eldred Dewey Wilson coined the phrase ‘Mazatzal Revolution’ to describe mountain building along the western edge of the North American craton. While the Mazatzal Revolution occurred in the Proterozoic – more than 1.6 billion years ago – it continues to influence Arizona geology and mineral exploration to this day. Wilson’s 1937 Ph.D. research is now available online for the first time.

In about 1920, twenty-two-year old Eldred Dewey Wilson joined a handful of geologists – N.H. Darton, Carl Lausen and Olaf P. Jenkins, among them – wrestling with the complex geology of the rugged mountains of southern and central Arizona. Wilson was an assistant geologist at the Arizona Bureau of Mines and working on his M.S. thesis, ‘The Mazatzal Quartzite, a new pre-Cambrian formation of central Arizona’ at the University of Arizona. In 1924 Wilson was promoted to geologist at the Bureau, where he remained, with a short leave of absence to begin his doctoral research in 1931-1932 at Harvard University, until his death in 1965.

Wilson set out in 1930 to address, ‘the chief features of pre-Cambrian regional structure within part of central Arizona’, for his Ph.D. dissertation – ‘‘The Pre-Cambrian Mazatzal Revolution in Central Arizona’. His field area included the Mazatzal Mountains, Pine Creek, eastern Tonto Basin or northern Sierra Ancha, Del Rio, and the southern Black Hills areas, all of which contained extensive outcrops of Proterozoic-age rocks. Wilson concluded from his observations of the field relationships of rocks and structures that the ‘principal features of regional structure originated from a great pre-Cambrian crustal disturbance’, which he called the ‘Mazatzal Revolution’.

Wilson’s ‘Mazatzal Revolution’ was an early contribution to deconstructing the processes responsible for the geology of central Arizona. He noted, ‘The subparallel folds, thrust faults, and imbricate, steeply dipping reverse faults clearly resulted from intense north­west-southeastward regional compression. The transverse faults are believed to have been formed, also during the compression, by shearing normal to the trend of the folds.’

Wilson hypothesized, too, that, ‘structural weaknesses inherited from the Mazatzal Revolution may have influenced the localization of many of Arizona’s prevailingly north­eastward-trending veins and the pattern of the Tertiary Basin and Range faulting.’ The orogenic Mazatzal Revolution continues to impact Arizona geology today.

E.D. Wilson ca. 1960s.

Reynolds & Others (2013) on Eldred Dewey Wilson’s contribution to Arizona geology. Wilson published a number of important papers on Arizona geology. According to Reynolds and others (2013), Eldred D. Wilson provided the first geologic map and cogent discussion of the geology and mineral resources of southern Yuma County: “Wilson mapped this hitherto unknown area of southwestern Arizona from 1929-1932. In the process, he discovered a new set of mountains that had been overlooked by previous geologists and explorers. He named this range the Butler Mountains after G. M. Butler, former Director of the Bureau and Dean of the College of Mining and Engineering (Wilson, 1931). Wilson was the first person to describe and map the geology of a large number of mountain ranges in southwestern Arizona. The data from Wilson’s 1933 geologic map were incorporated into the 1969 state geologic map.”

See James T. Forrester and Richard E. Moore’s ‘Memorial to Eldred Dewey Wilson 1898-1967’ for more about the life and times of Dr. Wilson.

Note: AZGS thanks an anonymous patron who arranged at his/her own expense with Harvard University to scan Wilson’s dissertation and secure copyright permission from Dewey Wilson to re-release Dr. Wilson’s work as CR-17-C.

References 
 
Forrester, J.T. and Moore, R.E., 1965 Memorial to Eldred Dewey Wilson 1898-1967. Geological Society of America Bulletin, V. 76, p. 187-191.

Reynolds, S., Spencer, J.E., Richard, S.M., Pearthree, P.A. 2013, The Geological Exploration of Arizona: The Role of State and Federal Surveys and the Geologic Map of Arizona, Arizona Geology Magazine, Winter 2013.

Wilson, E.D., 1922, The Mazatzal Quartzite, a new pre-Cambrian formation of central Arizona. Univ. of Arizona M.S. thesis, 40 p.

Wilson, E.D., 1937, The Pre-Cambrian Mazatzal Revolution in Central Arizona. Ph.D. Dissertation, Harvard University, Cambridge, MA, 335 p.

This post is reblogged from Arizona Geology

Site Investigation of Tributary Drainages to the San Pedro River, Arizona

The Arizona Geological Survey has just released a new paper: Site Investigation of Tributary Drainages to the San Pedro River, Arizona (Open-file Report OFR-15-02) which is available for free download at: http://repository.azgs.az.gov/uri_gin/azgs/dlio/1724

The paper begins:

In late 2013 the Arizona Geological Survey (AZGS) partnered with the Arizona Department of Water Resources (ADWR) to investigate sedimentary relationships at numerous sites along the San Pedro River in southeastern Arizona. This project supplemented previous work along the San Pedro River. In 2007, AZGS conducted surficial geologic mapping along the San Pedro River, Aravaipa Creek, and the Babocomari River. These maps and a report are available in AZGS DM-RM-1.2. The goal of the 2013 project was to conduct site investigations along the San Pedro River to determine whether sedimentary relationships between San Pedro River and tributary alluvium are accurately represented by their mapped location on the surface. This document includes a brief summary and description of sites along the San Pedro River visited by AZGS geologists in late 2013 and early 2014.

The report describes the geology of 39 sites with text, photos, and maps.

Related:

San Pedro River Geology – Implications for water law

West Antarctica ice-sheet calving due mainly to geology

Sometime between Monday 10th July and Wednesday 12th July, a 2,239 square mile section of Larsen C ice sheet finally broke away. As the media put it, that’s about the size of the State of Delaware. The Larsen C ice sheet is located in the Weddell Sea near the tip of the West Antarctica peninsula. The resulting iceberg has been designated Larson A68. Some of the media claimed this calving was due to human-induced global warming and portends a scary future. (See LA TimesNew York Times , and CNN stories. CNN headline: “That huge iceberg should freak you out” )

The LA Times story does note that in the year 2000, a 4,200 square mile chuck of ice calved from the Ross Sea ice shelf.

A scientist from Project MIDAS, a UK-based Antarctic research project investigating the effects of a warming climate on the Larsen C ice shelf in West Antarctica, said that they were “not aware of any link to human-induced climate change…” (Source)

The geology of West Antarctica is discussed in a long post by geologist James Kamis (read full post).

As shown on Kamis’ figure 2 above, West Antarctica is within a major rift zone which is pulling the continent apart. There are also 61 recognized volcanos on the surface, on the sea bed, and under the ice, all of which provide heat and tectonic instability. Kamis contends that the geology is driving ice shelf calving.

Calving of giant ice bergs is not a new phenomenon. A 1956 newspaper story found by Tony Heller of RealScience.com documents two large icebergs. One, spotted by a Navy icebreaker was 208 miles long and 60 miles wide (12,480 square miles, about the size of Massachusetts and Connecticut combined). During the same year another iceberg measuring 200 miles long and 10 miles wide calved from the Ross Ice Shelf. The same story notes that the Navy Hydrographic Office reports a 100 mile by 100 mile iceberg (10,000 square miles) spotted by a whaling ship in 1927. (Source) Remember that good coverage of ice shelf calving is made possible by satellite observation which began in 1979. Before that, it was by chance observation from ships.

See also:

The “Unstoppable Collapse” of the West Antarctic ice sheet

Geology is responsible for some phenomena blamed on global warming

A Simple Question for Climate Alarmists

Out of the wildfire and into the flood – Arizona Summer 2017

After several quiet years, Arizona has had a very active wildfire season. Halfway through 2017, just over 352,000 acres have been burned in Arizona by wildfires of >100 acres in size (Inciweb for Arizona: https://inciweb.nwcg.gov/state/3/). This was the worst fire season since the record burns of 2011, and is almost 4 times as many acres burned than in 2013 (Table 1; Southwest Coordination Center: https://gacc.nifc.gov/swcc, accessed July 12, 2017). While the worst part of the fire season is likely behind us, based on recent years we can expect to see more wildfires in the fall. Most of the 2017 burned acreage has been on land managed by the U.S. Forest Service (USFS), followed by Arizona State lands (AZFD), Bureau of Indian Affairs (BIA), and Bureau of Land Management (BLM).

As the monsoon season ramps up, it is time to be cognizant of potential post-fire flooding and debris flows. Both floods and debris flows pose significant hazards to human health, property and infrastructure, and both carry a significant amount of sediment, woody material and rocks. Debris flows can be more dangerous, however, as they resemble slurries of dense, fast-moving concrete that carry more sediment and woody debris and larger caliber rocks (maybe up to basketball sized rocks in floods and car or truck sized boulders in debris flows).

Wildfires significantly impact watershed hydrology, causing much more runoff to occur and frequently triggering post-fire floods and debris flows. In the absence of wildfire, unburned vegetation intercepts raindrops, mitigating the impacts of high-velocity drops on soils. Depending on the burn severity of the wildfire, interception of rainfall by plants can be severely reduced or completely eliminated. At the same time, infiltration of water into the soil is impeded by the presence of ash and fire-related changes to soils (e.g. hyper-dry soils, hydrophobicity, and the destruction of organic matter). These changes result in increased runoff volumes and velocities such that smaller, short-lived monsoon storms can generate tremendous runoff, flooding, and debris flows, and do a huge amount of geomorphic work (i.e. erosion and transportation of sediment) in a very short period of time.

Post by Ann Youberg

Read more at: http://arizonageology.blogspot.com/2017/07/out-of-wildfire-and-into-flood-arizona.html

Mineral Resources of some Arizona National Monuments

In view of President Trump’s program to reassess some National Monuments, the Arizona Geological Survey has released flyers regarding the mineral potential of four Arizona monuments: Ironwood Forest, Grand Canyon-Parashant, Sonoran Desert, and Vermilion Cliffs. You may read these short flyers here: http://repository.azgs.az.gov/uri_gin/azgs/dlio/1715

Ironwood Forest, about 35 miles northwest of Tucson, has an active copper mine and, according to local geologists, much more potential resources both east and west of the active mine. You can read about the history of the Silver Bell mine in a new paper by geologist David Briggs here: http://repository.azgs.az.gov/uri_gin/azgs/dlio/1714 Briggs notes: “Over the past 130 years, the Silver Bell mining district yielded approximately 2.27 billion pounds of copper, 6.6 million pounds of molybdenum, 3.7 million pounds of lead, 40.8 million pounds of zinc, 2,100 ounces of gold and 5.95 million ounces of silver.”

The Grand Canyon-Parashant area has produced copper, uranium, lead, zinc, gold, and Silver from breccia pipe deposits within what is now the monument. Breccia pipes are vertical pipe-like structures comprising broken rock (breccia). They are collapse features that originate in the cavernous Redwall Limestone and subsequently propagate upward through upper Paleozoic and lower Mesozoic rock formation. A recent review by the Arizona Geological Survey indicates that there could be thousands of yet unexplored breccia pipes within the monument. (See my article: Breccia pipes of northwestern Arizona and their economic significance)

The Sonoran Desert monument west of Phoenix has historically produced , gold, silver, copper, and manganese from small mines. The Aguila manganese mineral district in the Big Horn Mountains produced 42 million pounds of manganese.

The Vermilion Cliffs area in northwestern Arizona has had some small production of uranium, but the AZGS concludes “ there is little geologic evidence for economic minerals deposits in the monument.”

Two of the monuments, Ironwood Forest and Grand Canyon-Parashant, have had significant mineral production and more inferred resources. Local geologists suspect there are more copper resources east and west of the active mining area of the Silver Bell mine, but that ground is effectively off-limits because it lies within Ironwood Forest National Monument. The monument was imposed over valid pre-existing mining claims. This should be taken into account in assessing their status. The imposition of National Monument designation greatly inhibits or even prevents development of valuable mineral resources.

History of the Silver Bell Mining District

The Arizona Geological Survey has just released another paper about Arizona mining: The History of the Silver Bell Mining District (AZGS Contributed Report CR-17-A). The paper is authored by geologist and mining historian David Briggs who has written about many of Arizona’s mining districts. The paper is available for free download (link).

The Silver Bell mine and the town of Silverbell are located about 36 miles northwest of Tucson, Arizona. It has produced copper and other metals since 1873 and silver since 1865. Prior to that, the Tohono O’odham Indians and/or their predecessors mined turquoise, hematite and clay, which were used for pottery, paint and decorative purposes.

The Silver Bell mine has had a colorful and sometimes contentious history. Briggs writes that “Over the past 150 years, the Silver Bell mining district evolved from a collection of small, intermittent, poorly financed and managed underground mining operations that struggled to make a profit from high-grade ores; to a small but profitable producer, deploying innovative mining practices and advancements in technology to successfully develop the district’s large, low-grade copper resource.”

Besides a detailed history of owners and operations, the report contains many historic photographs of the mining operations and the town.

Briggs: “Over past 130 years, the Silver Bell mining district yielded approximately 2.27 billion pounds of copper, 6.6 million pounds of molybdenum, 3.7 million pounds of lead, 40.8 million pounds of zinc, 2,100 ounces of gold, and 5.95 million ounces of silver.”

The mine now produces copper by leaching and electro-winning. Remaining reserves are reported to be 214.4 million tons, averaging 0.283% copper. Local geologists suspect there are more copper resources east and west of the active mining area, but that ground is effectively off-limits because it lies within Ironwood Forest National Monument. The monument was imposed over valid pre-existing mining claims. IFNM is one being reconsidered by the Trump administration.

Other papers by David Briggs:

History of the Ajo Mining District, Pima County, Arizona

History of the Warren (Bisbee) Mining District

History of the San Manuel-Kalamazoo Mine, Pinal County, Arizona

Recovery of Copper by Solution Mining Techniques

Superior, Arizona – An Old Mining Camp with Many Lives

History of the Copper Mountain (Morenci) Mining District

History of Helvetia-Rosemont Mining District, Pima County, Arizona

History of the Ajo Mining District, Pima County, Arizona by David Briggs

Geologist David Briggs has written another interesting paper on the history of mining in Arizona. This 18-page paper, History of the Ajo Mining District, Pima County, Arizona, was just published by the Arizona Geological Survey and is available as a free download: http://repository.azgs.az.gov/uri_gin/azgs/dlio/1710

I was particularly interesting in the Ajo paper because as a geologist, I conducted exploration at the mine and in the district. Although the mine is now inactive, there is remaining mineralization that can be mined given the right economic conditions. The Ajo orebody is particularly interesting to geologists because paleomagnetic and geologic evidence indicates that the Ajo ore deposit has been tilted to the south a total of approximately 120 degrees in two separate tectonic events. (Source) There is also speculation that a detached piece of the original orebody lies hidden nearby.

Briggs begins his story as follows: “The hostile environment of southwestern Arizona’s low desert presented many challenges to those who sought to discover and exploit the mineral wealth

of the region. Ajo’s remote location combined with hot summer days and scarce water created a number of obstacles that needed to be overcome. Despite these impediments, the district’s wealth was mined by Native Americans long before the arrival of first Spanish explorers, who recognized its potential soon after establishing outposts in this region.”

The Ajo area has a long history. Prior to the arrival of the first Spanish explorers in the 1530’s, the native Tohono O’odham Indians and their ancestors mined hematite, an iron oxide, which they used as body paint. Establishment of Spanish missions in Southern Arizona provided bases from which prospectors combed the country.

With the signing of the Treaty of Guadalupe Hidalgo at the end of the Mexican American War on February 2, 1848, and the subsequent Gadsden Purchase in June 1854, many prospectors tried their luck at Ajo.

Briggs provides great detail as he recounts the many lives of mining ventures in Ajo. Following is a very brief sketch of major events.

The first formal mining began in 1855 and a wagon road was constructed to the railroad at Gila Bend. Ore was also sent by wagon to San Diego and shipped to Swansea, Wales for smelting. High transportation costs eventually made the venture uneconomic.

Briggs recounts the era between 1898 and 1908 when the Ajo deposit saw many promotions and fraudulent mining schemes.

In 1911, the Calumet and Arizona Mining Company, which was operating mines in Bisbee, became interested in the Ajo properties and acquired the New Cornelia Copper Company which owned Ajo at the time. Calumet began an extensive drilling program which confirmed the presence of a large sulfide body of mineralization. They began open pit mining in 1915.

In 1931, Phelps Dodge merged with Calumet and Arizona Mining Company and continued to operate the mine which they did until 1985 when a combination of low copper prices and stricter regulations for smelter air quality caused the company to close the mine.

The Ajo property is now owned by Freeport-McMoRan, Inc. through its merger with Phelps Dodge. According to Briggs, “Freeport continues to periodically assess the economic feasibility of returning the Ajo project to production. As of December 31, 2015, this project is estimated to contain a sulfide resource of 482 million short tons, averaging 0.40% copper, 0.010% molybdenum, 0.002 oz. of gold/ton and 0.023 oz. of silver/ton.”

Other papers by David Briggs, published by the Arizona Geological Survey:

History of the Warren (Bisbee) Mining District

History of the San Manuel-Kalamazoo Mine, Pinal County, Arizona

Recovery of Copper by Solution Mining Techniques

Superior, Arizona – An Old Mining Camp with Many Lives

History of the Copper Mountain (Morenci) Mining District

History of Helvetia-Rosemont Mining District, Pima County, Arizona

 

The Pirate Fault of Canada del Oro

pirate-fault

The Pirate fault forms the western boundary of the Santa Catalina Mountains near Tucson and separates the mountains from the Cañada del Oro basin to the west. The fault occurs just east of the communities of Saddlebrooke, Catalina, and Oro Valley. Remnants of this fault, exposed for about 15 miles along the mountain front, are described in a paper from the Arizona Geological Survey (see reference below). The paper describes geological features of 10 sites along the fault trace.

 

The AZGS says that this fault represents an expression of Basin & Range faulting which was active between 12 million and 6 million years ago. Vertical displacement on the fault is estimated to be about 2.5 miles with the west side down relative to the Santa Catalina Mountains uplift on the east. The fault dips from 50° to 55° west along its entire trace. The Basin & Range era was a time of crustal extension which formed much of the topography in Southern Arizona.

According to AZGS: “ Following cessation of active uplift, the fault was buried under detritus eroded from the uplifted Santa Catalina block and, currently, is being exhumed by the down-cutting Cañada del Oro and its tributaries. This field examination reveals the fault to have left a sparse but diverse collection of remains implying a varied history of fault development and evolution.”

“Deposition of basin-fill material in the Cañada del Oro basin culminated in Pleistocene time (1-2 Ma) following cessation of active uplift on the Pirate fault. Alluvium deposited during this latter time forms the high-stand surface of coalescent alluvial fans composed mostly of detritus eroded from the Santa Catalina Mountains.” That material contains placer gold deposits. The gold was derived from gold-bearing quartz veins in the Santa Catalina Mountains.

The Pirate fault disappears beneath alluvium to both the south and north. If one projects the northern trace, the Pirate fault could intersect the southeast-to-northwest trending Mogul fault. Indeed, near the projected intersection is a decorative stone quarry whose source rock is highly fractured, deformed, and altered bedrock that may be evidence of the projected fault intersection.

Parts of the exposed Pirate fault are stained red by hematite, an iron oxide, suggesting that mineralizing hydrothermal solutions were present during the development of the fault. The exact nature of this mineralization is enigmatic and according to the AZGS, “would seem to defy ready explanation.” “The picture that emerges is that of the Pirate fault as a geologic entity whose tenure as an active participant in the extensional Basin-Range tectonic event has left behind a somewhat sparse and locally enigmatic set of remains from which to infer, caveat emptor, its past.”
Reference:

Hoxie, D.T., Exhuming the Remains of the Inactive Mountain-Front Pirate Fault, Santa Catalina Mountains, Southeastern Arizona. Arizona Geological Survey, Contributed Report CR-12-F, 18p.

Free download: http://repository.azgs.az.gov/sites/default/files/dlio/files/nid1483/cr-12-f_pirate_fault_report_v.1.pdf

See also: The Gold of Cañada del Oro

The Basin & Range Province of North America