Bay mud
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Bay mud consists of thick deposits of soft, unconsolidated
silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when ...
y
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
, which is saturated with
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
; these soil layers are situated at the bottom of certain
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...
, which are normally in
temperate region In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
s that have experienced cyclical
glacial A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
cycles. Example locations are
Cape Cod Bay A cape is a clothing accessory or a sleeveless outer garment which drapes the wearer's back, arms, and chest, and connects at the neck. History Capes were common in medieval Europe, especially when combined with a hood in the chaperon. Th ...
, Chongming Dongtan Reserve in
Shanghai Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flow ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
,
Banc d'Arguin The Banc d'Arguin National Park ( ar, حوض أركين) of Bay of Arguin lies in Western Africa on the west coast of Mauritania between Nouakchott and Nouadhibou and is the former mouth of the Tamanrasset River. The World Heritage Site is a ...
preserve in
Mauritania Mauritania (; ar, موريتانيا, ', french: Mauritanie; Berber: ''Agawej'' or ''Cengit''; Pulaar: ''Moritani''; Wolof: ''Gànnaar''; Soninke:), officially the Islamic Republic of Mauritania ( ar, الجمهورية الإسلامية ...
, The
Bristol Channel The Bristol Channel ( cy, Môr Hafren, literal translation: "Severn Sea") is a major inlet in the island of Great Britain, separating South Wales from Devon and Somerset in South West England. It extends from the lower estuary of the River Seve ...
in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
, Mandø Island in the
Wadden Sea The Wadden Sea ( nl, Waddenzee ; german: Wattenmeer; nds, Wattensee or ; da, Vadehavet; fy, Waadsee, longname=yes; frr, di Heef) is an intertidal zone in the southeastern part of the North Sea. It lies between the coast of northwestern conti ...
in
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...
,
Florida Bay Florida Bay is the bay located between the southern end of the Florida mainland (the Florida Everglades) and the Florida Keys in the United States. It is a large, shallow estuary that while connected to the Gulf of Mexico, has limited exchange o ...
,
San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water from a ...
,
Bay of Fundy The Bay of Fundy (french: Baie de Fundy) is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. It is an arm of the Gulf of Maine. Its extremely high tidal range is the hi ...
,
Casco Bay Casco Bay is an inlet of the Gulf of Maine on the southern coast of Maine, New England, United States. Its easternmost approach is Cape Small and its westernmost approach is Two Lights in Cape Elizabeth. The city of Portland sits along its south ...
,
Penobscot Bay Penobscot Bay (french: Baie de Penobscot) is an inlet of the Gulf of Maine and Atlantic Ocean in south central Maine. The bay originates from the mouth of Maine's Penobscot River, downriver from Belfast, Maine, Belfast. Penobscot Bay has many ...
, and
Morro Bay Morro Bay (''Morro'', Spanish for "Hill") is a seaside city in San Luis Obispo County, California. Located on the Central Coast of California, the city population was 10,757 as of the 2020 census, up from 10,234 at the 2010 census. The town ...
. Bay mud manifests low
shear strength In engineering, shear strength is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a materia ...
, high
compressibility In thermodynamics and fluid mechanics, the compressibility (also known as the coefficient of compressibility or, if the temperature is held constant, the isothermal compressibility) is a measure of the instantaneous relative volume change of a fl ...
and low permeability, making it hazardous to build upon in
seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
ally active regions like the
San Francisco Bay Area The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area Go ...
. Typical bulk density of bay mud is approximately 1.3 grams per cubic centimetre. Bay muds often have a high organic content, consisting of decayed organisms at lower depths, but may also contain living creatures when they occur at the upper soil layer and become exposed by low tides; then, they are called
mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...
s, an important
ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
zone for
shorebird 245px, A flock of Dunlins and Red knots">Red_knot.html" ;"title="Dunlins and Red knot">Dunlins and Red knots Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflat ...
s and many types of marine organisms. Great attention was not given to the incidence of deeper bay muds until the 1960s and 1970s when development encroachment on certain North American bays intensified, requiring geotechnical design of foundations. Bay mud has its own official geological abbreviation. The designation for
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
older bay mud is Qobm and the acronym for Quaternary younger bay mud is Qybm. An
alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...
layer is often found overlying the older bay mud. In relation to shipping channels, it is often necessary to dredge bay bottoms and barge the excavated material to an alternate location. In this case
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...
analyses are usually performed on the bay mud to determine whether there are elevated levels of heavy metals,
PCB PCB may refer to: Science and technology * Polychlorinated biphenyl, an organic chlorine compound, now recognized as an environmental toxin and classified as a persistent organic pollutant * Printed circuit board, a board used in electronics * ...
s or other toxic substances known to accumulate in a
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
environment. It is not uncommon to dredge the same
channel Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austral ...
repeatedly (over a span of ten to thirty years) since further settling sediments are prone to redeposit on an open estuarine valley floor.


Depositional scenarios

Bay muds originate from two generalized sources. First
alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...
deposits of clays, silts and sand occur from streams tributary to a given bay. The extent of these unconsolidated interglacial deposits typically ranges throughout a given bay to the extent of the historical perimeter
marshland A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
s. Second, in periods of high glaciation, deposits of silts, sands and organic plus
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
(e.g. decomposition of estuarine
diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s) may form a separate distinct layer. Thus bay muds are important time records of glacial activity and streamflow throughout the
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
period. Some depositional formation is quite recent, such as in the case of Florida Bay, where much of the bay mud has accumulated since 2000 BCE, and consists of primarily decayed organic material. In the case of Florida Bay these bay muds can accrete as much as 0.5 to 2.0 centimeters per annum, although the dynamic equilibrium of
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
,
wave action In fluid dynamics, a wind wave, water wave, or wind-generated water wave, is a surface wave that occurs on the free surface of bodies of water as a result from the wind blowing over the water surface. The contact distance in the direction of t ...
redistribution and deposition complicate the net rate of layer growth. In the case of the
Bristol Channel The Bristol Channel ( cy, Môr Hafren, literal translation: "Severn Sea") is a major inlet in the island of Great Britain, separating South Wales from Devon and Somerset in South West England. It extends from the lower estuary of the River Seve ...
in the United Kingdom bay, mud formation has been occurring at least since the Eemian Stage (known as the
Sangamonian The Sangamonian Stage (or Sangamon interglacial) is the term used in North America to designate the last interglacial period. In its most common usage, it is used for the period of time between 75,000 and 125,000 BP.Willman, H.B., and J.C. Frye, 1 ...
Stage in
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
), or about 130,000 years ago. In other cases such as with
San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water from a ...
, deposition has been interrupted by sea-level changes, and strata of vastly different vintages are found. In the San Francisco Bay Area, these are called Young bay mud and
Older bay mud Older is the comparative form of "old". It may also refer to: Music: * ''Older'' (album), the third studio album from George Michael (released in 1996) ** "Older" (George Michael song) * "Older", a song on the 1999 album ''Long Tall Weekend'' ...
by
geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
s. Human activities can also affect deposition; close to half of the Young Bay Mud in San Francisco Bay was placed in the period 1855–1865, as a result of
placer mining Placer mining () is the mining of stream bed (Alluvium, alluvial) deposits for minerals. This may be done by open-pit mining, open-pit (also called open-cast mining) or by various surface excavating equipment or tunneling equipment. Placer minin ...
in the
Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...
foothills.


Geotechnical factors

Construction on bay mud sites is difficult because of the soil's low strength and high compressibility. Very lightweight buildings can be constructed on bay mud sites if there is a thick enough layer of non-bay-mud soil above the bay mud, but buildings which impose significant loads must be supported on deep foundations bearing on stiffer layers below the bay mud, or obtaining support from friction in the bay mud. Even with deep foundations, difficulties arise because the surrounding ground will likely settle over time, potentially damaging utility connections to the building and causing the entryway to sink below street level. A number of notable buildings have been constructed over bay muds, typically employing special mitigation designs to withstand seismic risks and settlement issues. Complicating design issues, fill (beginning about 1850 AD) is sometimes found deposited on the surface level. For example, the
Dakin Building The Dakin Building is an architectural award-winning class A office building on the San Francisco Bay in Brisbane, California. Serving as a corporate headquarters building for several companies of national prominence, it was built from the profit ...
in
Brisbane, California Brisbane (pron. , unlike Brisbane, Queensland, Australia) is a small city located in California in the northern part of San Mateo County on the lower slopes of San Bruno Mountain. It is located on the southern border of San Francisco, on the ...
was designed in 1985 to sit on piles 150 feet deep, anchoring to the
Franciscan formation The Franciscan Complex or Franciscan Assemblage is a geologic term for a late Mesozoic terrane of heterogeneous rocks found throughout the California Coast Ranges, and particularly on the San Francisco Peninsula. It was named by geologist Andrew ...
, below the bay muds and through an upper fill layer. Furthermore, the structure's entrance ramp has been set on a giant hinge to allow the surrounding land to settle, while the building absolute height remains constant. The Crowne Plaza high-rise
hotel A hotel is an establishment that provides paid lodging on a short-term basis. Facilities provided inside a hotel room may range from a modest-quality mattress in a small room to large suites with bigger, higher-quality beds, a dresser, a ref ...
in
Burlingame, California Burlingame () is a city in San Mateo County, California. It is located on the San Francisco Peninsula and has a significant shoreline on San Francisco Bay. The city is named after diplomat Anson Burlingame and is known for its numerous eucalyp ...
was also designed to sit over bay muds, as was the Westin Hotel in
Millbrae, California Millbrae is a city located in northern San Mateo County, California, United States. To its northeast is San Francisco International Airport, San Bruno is on its northwest, and Burlingame on its southeast. It is bordered by San Andreas Lake to ...
and Trinity Church in Boston's Copley Square. Indeed, Boston's entire
Back Bay Back Bay is an officially recognized neighborhood of Boston, Massachusetts, built on reclaimed land in the Charles River basin. Construction began in 1859, as the demand for luxury housing exceeded the availability in the city at the time, and t ...
district is named for the tidal bay that it now covers.
Logan International Airport General Edward Lawrence Logan International Airport , also known as Boston Logan International Airport and commonly as Boston Logan, Logan Airport or simply Logan, is an international airport that is located mostly in East Boston and partially ...
and the
San Francisco International Airport San Francisco International Airport is an international airport in an unincorporated area of San Mateo County, south of Downtown San Francisco. It has flights to points throughout North America and is a major gateway to Europe, the Middle E ...
are also constructed over bay mud.


Mudflats

When the mud layer is exposed at the tidal fringe, mudflats result affording a unique
ecotone An ecotone is a transition area between two biological communities, where two communities meet and integrate. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and gras ...
that affords numerous shorebird
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
a safe feeding and resting habitat. Because the muds function much like
quicksand Quicksand is a colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a ...
, heavier
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
ian
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s not only cannot gain traction for pursuit, but would actually become trapped in the sinking muds. The muds are also an important substrate for primary
marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...
productivity including
eelgrass Eelgrass is a common name for several plants and may refer to: * ''Zostera'', marine eelgrass * ''Vallisneria'', freshwater eelgrass {{Short pages monitor