Two weeks ago, my basement flooded in Utah. In the midst of dealing with it, I came across a special issue of Orion: Nature and Culture on flood stories and “how to stay afloat.” I have selected two of the articles on flood geology to share in this edition of Core Elements.
Starting with this edition, we will also have a Quiz of the Week on geoscience and energy. I hope you will enjoy thinking about and answering these questions.
Rasoul Sorkhabi
Editor, Core Elements
Downstream Floods in Houston
Cire Notrevo/Shutterstock.com
Author Lacy Johnson lives in Houston and recently covered historic flooding and antiflooding measures. Her story was motivated by her experiences in 2017 during Hurricane Harvey.
Flood geography:
Houston was built on forested land, marshes, and coastal prairies at the confluence of Buffalo and White Oak bayous.
At the time of its founding, the bayous were shallow streams—each a few feet deep—surrounded by trees.
Houston’s climate and location make the city prone to storms and floods.
Historic floods in Houston:
The first recorded flood in Houston occurred in April 1837, only eight months after the city was founded. Houston flooded again that May, and again in 1843, 1854, and 1875.
On September 8, 1900, a Category 4 hurricane leveled the port of Galveston, south of Houston, killing 6,000 people.
Buffalo Bayou flooded again in 1907 and 1908.
Houston Plan:
In 1909, Houston’s mayor led a delegation to Washington to present the “Houston Plan” to the Congress.
The plan was to carve a channel—25 miles long, 150 feet wide, and 25 feet deep—out of Buffalo Bayou for ships to navigate.
The Harris County Houston Ship Channel opened in 1914. The mayor’s daughter christened it “Port Houston.”
Flood control:
More floods hit Houston in 1915, 1929, and 1935.
In 1937, the Texas Legislature created the Harris County Flood Control District (HCFCD). It had the authority to carry out a large-scale flood mitigation project with the Army Corps of Engineers.
The Corps constructed two reservoirs along Buffalo Bayou in 1945 and 1948, but flooding continued into the 1950s.
The HCFCD decided to carry out “channel rectification” projects: To deepen, widen, and straighten the bayous by clearing the trees and shrubs along the banks and paving them with concrete.
Floods are natural processes and cannot be avoided: Concrete channels mitigate flooding in some areas but export it to other areas.
The story continues:
Today, more than 7 million people live in the Greater Houston area, and it has been an oil capital since roughly 1948.
Floods still affect Houston from time to time, as they do across the Gulf coastal plain from Texas to Florida.
The benefits: The author of the article also mentions how floods benefit the land and neighboring ecosystems.
Floods help remove invasive species and obstructions from riverbeds.
They bring nutrients from the land where they happen to the plants and animals that need them in the bay.
Flooding helps carry sediment to places where soil has been eroded.
“Echo of a Cataclysm” in Orion magazine reports on the ancient floods caused by glacial lake outbursts in Washington, Oregon, Idaho and Montana.
Missoula floods:
The author opens, saying: “The town Missoula in Montana begins when a steep, fifty-mile corridor of pine, fir, and tamarack ends, at the site the Clark Fork River exits Hellgate Canyon.”
Clark Fork River in Montana is a tributary of the Columbia River, named after explorer Wiliam Clark in 1806 by his fellow traveler Meriwether Lewis.
A French fur trapper called this confluence Port of Hell; Native Salish people described it as the River of Ambush.
How did this canyon form?
During the last ice age, the Clark Fork River poured into a valley blocked by an ice dam, near Sandpoint, Idaho, where there is still a lake called Pend Oreille.
Over thousands of years, the glacial lake burst more than 100 times, each creating a biblical deluge.
These floods rushed down the Clark River as well as the rest of Columbia River in Idaho, Washington, and Oregon, and created the entire Columbia River Gorge.
J. Harlen Bretz:
The records of these glacial floods, known as Missoula Floods, were discovered in the 1920s by geologist J. Harlen Bretz.
Bretz found out-of-place boulders (erratic rock), unusual sandbars, ripple marks, and other evidence of massive floods on the Columbian Plateau.
Missoula floods have also been called the Bretz floods.
Go deeper: John Soennichsen’s 2008 bookBretz’s Flood: The Remarkable Story of a Rebel Geologist and the World's Greatest Flood is the definite volume on this subject.
Why it matters: Glacial lake outbursts of the last Ice Age are not confined to the Columbia Plateau. They are also found in the northeastern U.S, including:
Paleo-lake Tonawanda in western New York, which drained and created Niagara Falls
Lake Agassiz, the largest glacial lake in North America, which once stretched from Canada’s Manitoba to Minnesota
Today, as we are dealing with a new stage of glacial melts and resulting floods, the chronicles of the past prompt us to “remember beyond history,” as the Orion article suggests.
What are the differences between claystone, mudstone, shale, black shale, and marl?
Please send your responses via email to editorial@aapg.org, and I will select the one that provides the most concise and accurate answer to publish in the next edition with credit to the responder.
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