remiconnesson/oceanservice-noaa-facts huggingface dataset:
# How does sand form?

The environmentalist [Rachel Carson](https://blog.response.restoration.noaa.gov/rachel-carson-biologist-writer-role-model) wrote, "In every curving beach, in every grain of sand, there is a story of the Earth."

Sand comes from many locations, sources, and environments. Sand forms when rocks break down from weathering and eroding over thousands and even millions of years. Rocks take time to decompose, especially quartz (silica) and feldspar.

Often starting thousands of miles from the ocean, rocks slowly travel down rivers and streams, constantly breaking down along the way. Once they make it to the ocean, they further erode from the constant action of waves and tides.

The tan color of most sand beaches is the result of iron oxide, which tints quartz a light brown, and feldspar, which is brown to tan in its original form. Black sand comes from eroded volcanic material such as lava, basalt rocks, and other dark-colored rocks and minerals, and is typically found on beaches near volcanic activity. Black-sand beaches are common in Hawaii, the Canary Islands, and the Aleutians.

The by-products of living things also play an important part in creating sandy beaches. Bermuda's preponderance of pleasantly pink beaches results from the perpetual decay of single-celled, shelled organisms called [foraminifera](http://oceanexplorer.noaa.gov/explorations/islands01/log/sep28/media/planktonic.html).

Less common but no less inviting beaches, devoid of quartz as a source of sand, rely on an entirely different ecologic process. The famous white-sand beaches of Hawaii, for example, actually come from the poop of parrotfish. The fish bite and scrape algae off of rocks and dead corals with their parrot-like beaks, grind up the inedible calcium-carbonate reef material (made mostly of coral skeletons) in their guts, and then excrete it as sand. At the same time that it helps to maintain a diverse coral-reef ecosystem, parrotfish can produce hundreds of pounds of white sand each year!

So the next time you unfurl your beach towel down by the shore, ponder the sand beneath you, which, as Rachel Carson said, is telling you a story about the Earth. You may be about to comfortably nestle down in the remains of million-year-old rocks. Then again, you may soon come to rest upon an endless heap of parrotfish poop.

Did you know? - Sand is measured according to specific parameters. If more than 50 percent of the material is larger in diameter than 75 microns (.03 inches) but smaller than .18 inches, it is said to be sand. If the average particle size is smaller, it is considered to be silt or clay, and if the average particle size is larger, it is garden-variety gravel.

- [What is a living shoreline?](https://oceanservice.noaa.gov/facts/living-shoreline.html)

-
# What is a canal?

![The Gowanus canal at Carroll Street where some of the highest sediment contamination is found](/facts/gowanus-canal.jpg "The Gowanus canal at Carroll Street where some of the highest sediment contamination is found")

The Gowanus Canal was built in the mid-1800s and once served as a major commercial route to New York Harbor. A variety of industries that operated along its banks released contaminants into the canal. Sewer overflows also contribute to the pollution, which negatively impacts fishing and recreation for nearby residents. NOAA is working with the U.S. Environmental Protection Agency and the City of New York to assess the damage and propose ways to mitigate it.

A canal is a human-made waterway that allows boats and ships to pass from one body of water to another. Canals are also used to transport water for irrigation and other human uses. While the advent of more efficient forms of transportation has reduced the need for canals, they still play a vital role as conduits for transportation and fostering global commerce.

There are two types of canals: waterways and aqueducts. Waterways are the navigable parts of a body of water, and can be located within a bay or open sea, can connect two or more waterbodies, or may even form networks within a city. Aqueducts are used exclusively to transport water for drinking, agriculture, and hydroelectric power.

The word "canal" derives from the Old French word chanel, which means “channel.” The oldest known canals are aqueducts built in Mesopotamia thousands of years ago. Since then, canals have played an important role in connecting cultures and facilitating commerce.

The Panama Canal, which connects the Atlantic and Pacific Oceans, was expanded in 2016 to accommodate modern large-scale cargo ships. NOAA played a role in ensuring that the shipment of goods through the larger canal would remain safe and efficient. [NOAA’s Navigation Response Teams](/facts/nrt.html) assisted the Panama Canal Authority by [participating in exercises](https://response.restoration.noaa.gov/about/media/panama-canal-authority-us-national-response-team-annual-emergency-response-exercise.html) to ensure that evacuation plans and safety precautions were operational in the event of an emergency. [NOAA also installed its](https://tidesandcurrents.noaa.gov/ports.html) [Physical Oceanographic Real-Time System (PORTS®)](https://tidesandcurrents.noaa.gov/ports.html) system at PortMiami, allowing super-sized ships that pass through the Panama Canal to safely and efficiently enter the busy U.S. seaport.

Did you know? - [What is the Great Loop?](https://oceanservice.noaa.gov/facts/great-loop.html)

- [NOAA’s Navigation Response Team](https://oceanservice.noaa.gov/facts/nrt.html)

- [Physical Oceanographic Real-Time System (PORTS®)](https://tidesandcurrents.noaa.gov/ports.html)

- [Gowanus Canal](https://darrp.noaa.gov/hazardous-waste/gowanus-canal)

-
# Do We Still Need Lighthouses?

![Point Arena Lighthouse](/facts/lighthouse960.jpg "Point Arena Lighthouse, Greater Farallones National Marine Sanctuary")

_[Point Arena Lighthouse](https://farallones.noaa.gov/about/history.html), which sits near the northern boundary of [Greater Farallones National Marine Sanctuary](https://farallones.noaa.gov/). Image credit: Robert Schwemmer_

Lighthouses and [beacons](/facts/totten-beacons.html) are towers with bright lights and fog horns located at important or dangerous locations. They can be found on rocky cliffs or sandy shoals on land, on wave-swept reefs in the sea, and at entrances to harbors and bays. They serve to warn mariners of dangerous shallows and perilous rocky coasts, and they help guide vessels safely into and out of harbors. The messages of these long-trusted aids to navigation are simple: either **STAY AWAY, DANGER, BEWARE!** or **COME THIS WAY!**

While lighthouses still guide seafarers, nowadays, [the Global Positioning System (GPS)](/facts/gps.html), NOAA’s [nautical charts](https://nauticalcharts.noaa.gov/), lighted navigational aids, buoys, radar beacons, and other aids to navigation effectively warn mariners of dangerous areas and guide them to safe harbors. Some 48,000 federal buoys, beacons, and electronic aids of the [marine transportation system](/navigation/marinenav/) mark more than 25,000 miles of waterways, harbor channels, and inland, intracoastal and coastal waterways, and serve more than 300 ports.

On August 7, 1789, Congress approved the [Lighthouse Act](https://www.nps.gov/maritime/nhlpa/handbook/HistoricLighthousePreservationHandbook_04_Part2.pdf)—the first public works program undertaken by the new federal government—which established and supported lighthouses, beacons, buoys, and public piers. Members of Congress thought the bill was so important that they passed the measure even before they established pay for themselves!

August 7 Is recognized as National Lighthouse Day. Even with the advent of advanced navigation technology, many lighthouses still sparkle for seafarers.

Did you know? - *While many lighthouses still shine, cartographers in NOAA’s Office of Coast Survey practice the art and science of designing, compiling, updating, and distributing [Electronic Navigational Charts](https://nauticalcharts.noaa.gov/charts/noaa-enc.html). These charts are specifically tailored to the needs of marine navigation.*

- [Electronic Navigational Charts](https://nauticalcharts.noaa.gov/charts/noaa-enc.html)

- [Office of Coast Survey](https://nauticalcharts.noaa.gov/)

- [Beacons of History: The Women Lighthouse Keepers of National Marine Sanctuaries](https://sanctuaries.noaa.gov/news/may23/beacons-of-history.html)

- [Sentinels of the Sanctuaries](https://sanctuaries.noaa.gov/magazine/3/sentinels-of-the-sanctuaries/)

- [Historic Navigation (Florida Keys National Marine Sanctuary)](https://floridakeys.noaa.gov/historic-navigation-aids/historicnav.html)

-
# What do leeward and windward mean?

##### **Did you know?**

_In sailing terminology, windward means "upwind," or the direction from which the wind is blowing. A windward vessel refers to one that is upwind of another vessel; a leeward vessel is downwind. In naval warfare during the [Age of Sail](/navigation/nautical-terms.html), windward ships had the advantage due to much greater maneuverability than their leeward (downwind) foes._

Did you know? - *In sailing terminology, windward means "upwind," or the direction from which the wind is blowing. A windward vessel refers to one that is upwind of another vessel; a leeward vessel is downwind. In naval warfare during the [Age of Sail](https://oceanservice.noaa.gov/navigation/nautical-terms.html), windward ships had the advantage due to much greater maneuverability than their leeward (downwind) foes.*
# What are brain corals?

## Brain corals, a **slow-growing** species of coral, often act as **foundations for reefs**.

![brain coral](/facts/brain-coral.jpg)

Brain coral in the Dry Tortugas, Florida.

The cerebral-looking organisms known as brain corals do not have brains, but they can grow six feet tall and live for up to 900 years! Found in the Caribbean, Atlantic, and Pacific Oceans, brain corals display what is known as Meandroid tissue integration. This means that the [polyps](/facts/coral.html), which are the basic living unit of corals, are highly associated to one another. Their tissues are more closely connected than those of other corals and are not separated by skeletal structures. Many researchers think that the more integrated a coral's polyp tissue is, the more advanced the coral species.

Tissue integration is advantageous because the coral polyps are able to transfer molecules such as nutrients, hormones, and oxygen—making it easier for the brain coral colony to communicate. In some cases, however, this can lead to vulnerability, because if even one polyp gets sick, the [pathogen](/education/kits/corals/coral10_disease.html) can quickly spread to the rest of the colony. Some species of brain corals suffer mass mortalities due to diseases such as black band disease, white plague, and thermal [bleaching](/facts/coral_bleach.html).

###### Get **Social**

###### More **Information**

Did you know?

The ecological importance of brain corals is enormous. Brain corals grow very slowly, but they build super strong structures that act as the foundations of coral reefs. They are known as [massive growth type](/education/kits/corals/media/supp_coral03h.html) corals. Massive corals take a long time to get big, but once they do, they offer outstanding protection to marine life and coastlines. Coral reefs can absorb up to 97 percent of the wave energy during storm events, and brain corals play an important role in that function. 

![](/bootstrap/img/shadow1.png)

**Last updated:** 06/16/24  
**Author:** NOAA  
[How to cite this article](/about/faq.html)

[Contact Us](/contact.html)

Did you know? - 

- The ecological importance of brain corals is enormous. Brain corals grow very slowly, but they build super strong structures that act as the foundations of coral reefs. They are known as [massive growth type](https://oceanservice.noaa.gov/education/kits/corals/media/supp_coral03h.html) corals. Massive corals take a long time to get big, but once they do, they offer outstanding protection to marine life and coastlines. Coral reefs can absorb up to 97 percent of the wave energy during storm events, and brain corals play an important role in that function.
# How many high tides are there per day?

![Monterey Bay National Marine Sanctuary](/facts/monterey-bay.jpg)

_If the Earth were a perfect sphere without large continents, and if the earth-moon-sun system were in perfect alignment, every place would get two equal high and low tides every day. However, the alignment of the moon and sun relative to Earth, the presence of the continents, regional geography and features on the seafloor, among other factors, make tidal patterns more complex._

##### **What is _Mean Higher High Water?_**

You might have bumped into this term while trying to find out when you’ll experience high tide where you live. Many coastal places actually have two high tides a day. Mean Higher High Water (MHHW) is the **average of the higher of the two daily high tides**. The term MHHW is more precise than “high tide,” and it helps specialists in the field communicate clearly about the tides they track. Problematic flooding can happen when water levels climb even a bit higher than normal variations in MHHW at a particular location. This is commonly called high tide flooding, and it can inundate roads, compromise stormwater systems, and damage coastal property.

While some places have one high tide and one low tide per day, most coastal locations have two high tides and two low tides a day. These highs and lows typically aren't equal. This is why, in most places, using the phrase "high tide" might be unclear. There's actually high tide and higher high tide (and low and lower low tide).

If the Earth were a perfect sphere without large continents, and if the earth-moon-sun system were in perfect alignment, every place would get two equal high and low tides every day. However, the alignment of the moon and sun relative to Earth, the presence of the continents, regional geography, and features on the seafloor, among other factors, make tidal patterns more complex.

Around the world, there are three basic tidal patterns: semidiurnal, mixed, and diurnal. When both high tides are about equal to each other, and the low tides are also roughly equal, the pattern is called a semidiurnal tide. If the two highs and lows differ substantially, the pattern is called a mixed tide. Where there's only one high and one low tide a day, it's called a diurnal tide. One location can experience different tide patterns throughout the month.
# What causes a sea turtle to be born male or female?

![a sea turtle](/facts/turtle-sex.jpg "a sea turtle")

_A Green turtle hatchling heads to sea in the northwest Hawaiian islands. Credit: Mark Sullivan, NOAA Permit 10137-07_

In most species, sex is determined during fertilization. However, the sex of most [turtles](https://oceanservice.noaa.gov/facts/turtle-hatch.html), alligators, and crocodiles is determined after fertilization. The temperature of the developing eggs is what decides whether the offspring will be male or female. This is called temperature-dependent sex determination, or TSD.

Research shows that if a turtle's eggs incubate below 27.7° Celsius (81.86° Fahrenheit), the turtle hatchlings will be male. If the eggs incubate above 31° Celsius (88.8° Fahrenheit), however, the hatchlings will be female. Temperatures that fluctuate between the two extremes will produce a mix of male and female baby turtles.

Researchers have also noted that the warmer the sand, the higher the ratio of female turtles. As the Earth experiences climate change, increased temperatures could result in skewed and even lethal incubation conditions, which would impact turtle species and other reptiles.

Did you know? - *Current research suggests that warming trends due to climate change may result in more female turtles being born!*

- [How do sea turtles hatch? (video)](https://oceanservice.noaa.gov/facts/turtle-hatch.html)

- [What do you know about the sea turtle?](https://oceanservice.noaa.gov/news/june15/sea-turtles.html)

- [What makes the green turtle...green?](https://oceanservice.noaa.gov/facts/green-turtle.html)

- [What is the largest sea turtle?](https://oceanservice.noaa.gov/facts/leatherback.html)

- [Sea turtles: NOAA Fisheries resources](http://www.nmfs.noaa.gov/pr/species/turtles/photos.html)

-
# What are the oldest living animals in the world?

##### **Did you know?**

_People often mistake corals for plants or even rocks, but corals actually consist of colonies of living invertebrate animals._

##### More **Information**

##### [Get **Social**](/socialmedia.html)

Did you know? - *People often mistake corals for plants or even rocks, but corals actually consist of colonies of living invertebrate animals.*

- [Are corals animals or plants?](https://oceanservice.noaa.gov/facts/coral.html)

- [What is a coral reef made of?](https://oceanservice.noaa.gov/facts/coralmadeof.html)

- [Corals much older than previously thought, study finds](http://news.psu.edu/story/439785/2016/11/30/research/corals-much-older-previously-thought-study-finds)

-
# How do hurricanes form?

##### **Did you know?**

_Less than one percent of algal blooms actually produce toxins. Not all algal blooms are harmful, and some may actually be beneficial. Phytoplankton are microscopic algae that form the base of the marine food web, and therefore, all other life in the ocean relies on them. Blooms can also be good indicators of environmental changes not only in the water, but also on land._

##### More **Information**

##### [Get **Social**](/socialmedia.html)

Did you know? - *Less than one percent of algal blooms actually produce toxins. Not all algal blooms are harmful, and some may actually be beneficial. Phytoplankton are microscopic algae that form the base of the marine food web, and therefore, all other life in the ocean relies on them. Blooms can also be good indicators of environmental changes not only in the water, but also on land.*

- [Hurricanes: Preparedness, Response, Recovery](https://oceanservice.noaa.gov/hazards/hurricanes/)

- [Ocean Today: Fuel for the Storm](https://oceantoday.noaa.gov/fuelforthestorm/)

- [Why do we name tropical storms?](https://oceanservice.noaa.gov/facts/storm-names.html)

- [National Hurricane Center](http://www.nhc.noaa.gov/)

- [Ready.gov](https://www.ready.gov/)

-
# Are all fish cold-blooded?

![an opah swimming in the open ocean](/facts/opah.jpg "an opah swimming in the open ocean")

_The opah, the only known fully warm-blooded fish, is a valuable species for commercial and recreational fishermen. However, researchers do not have a full understanding of the basic biology and ecology of this species. NOAA's Southwest Fisheries Science Center began collecting biological samples from opah in 2009 and initiated an electronic tagging program in 2011. Scientists hope to continue tagging opah to learn about their movements and range. This research will provide the basic life history information necessary for future population assessments and management. NOAA Fisheries is also working with the seafood industry to help reduce waste during the processing of opah._

Not all fish are cold-blooded. In 2015, researchers with the [NOAA Southwest Fisheries Science Center](https://swfsc.noaa.gov/) revealed the opah, or moonfish, as the first fully warm-blooded fish. Although not as warm as mammals and birds, the opah circulates heated blood throughout its body, giving it a competitive advantage in the cold ocean depths from 150 to 1,300 feet below the surface.

Its body temperature isn’t the only thing that makes this fish stand out from the rest in its environment. Most fish living in the dark and chilly depths rely on ambush to catch their prey, but the agile opah is fast and efficient, flapping its bright red pectoral fins to race through the water. The constant flapping of its fins heats the opah’s body, speeding its metabolism, movement, and reaction times.

About the same size as a large automobile tire, the opah is equipped with specialized blood vessels that carry warm blood to its gills to rewarm the blood that cools as the fish breathes and absorbs oxygen from the water. These heat-exchanging blood vessels minimize the loss of body heat to the opah’s cold environment, ensuring a warm core body temperature, increasing muscle output and swimming capacity, and boosting eye and brain function. The opah is also able to stay in deep water longer without risking reduced function to its heart and other organs because the fatty tissue surrounding its gills, heart, and muscle tissue acts as insulation against icy waters.

The opah is one of the most colorful of the commercial fish species, and is particularly popular in Hawaii. It is overall red with white spots and turns a silvery-grey when it dies. Its fins are crimson, and its large eyes are with gold. The fish’s large, round profile is thought to be the origin of its “moonfish” nickname. These combined characteristics certainly make this “warm-blooded fish” unique among the many wondrous creatures of the ocean.

Did you know? - *A few other fish such as tuna and some sharks warm certain parts of their bodies, boosting their swimming performance. But internal organs including their hearts cool off quickly and begin to slow down when they dive into cold depths, forcing them to return to shallower depths to warm up.*

- [Warm Blood Makes Opah an Agile Predator (NOAA Southwest Science Fisheries Center)](https://swfsc.noaa.gov/news.aspx?ParentMenuId=39&id=20466)

-
# Where do fish go when it freezes outside?

## Most fish **slow down and "rest" near the bottom** during cold winter months.

![White Shoal Lighthouse in northern Lake Michigan. (Courtesy Dick Moehl, Great Lakes Lighthouse Keepers Association)](/facts/frozenfish.jpg "White Shoal Lighthouse in northern Lake Michigan. (Courtesy Dick Moehl, Great Lakes Lighthouse Keepers Association)")

White Shoal Lighthouse in northern Lake Michigan.

Have you ever wondered how fish survive in cold winter weather, or where they go when lakes and ponds freeze over?

Like many people, fish tend to be less active in the cold. As cold-blooded creatures, their metabolism dips when temperatures take a dive.

The layer of ice that forms on top of a lake, pond, river, or stream provides some insulation that helps the waterbody retain its heat. Because warm water sinks in very cold freshwater, fish in these water bodies often gather in groups near the bottom. Some species, like koi and gobies, may burrow into soft sediments and go dormant like frogs and other amphibians, but most fish simply school in the deepest pools and take a "winter rest."

In this resting state, fishes' hearts slow down, their needs for food and oxygen decrease, and they move about very little. If you've ever gone ice fishing, you know that a long line, a slow, colorful lure, and a hearty portion of patience are often required to land this quiet quarry! Popular ice-fishing species include walleye, northern pike, yellow perch, and rainbow trout.

Did you know?

Just like the human "snowbirds" who fly south for the winter, saltwater fish often cruise to warmer climes when the mercury plummets. With the exceptions of the polar regions, salty ocean water rarely freezes. Oceangoing species also tend to stay near the bottom, where warmer water and swifter currents prevail.

![](/bootstrap/img/shadow1.png)

###### More **Information**

###### Get **Social**

**Last updated:** 06/16/24  
**Author:** NOAA  
[How to cite this article](/about/faq.html)

[Contact Us](/contact.html)

Did you know? - 

- Just like the human "snowbirds" who fly south for the winter, saltwater fish often cruise to warmer climes when the mercury plummets. With the exceptions of the polar regions, salty ocean water rarely freezes. Oceangoing species also tend to stay near the bottom, where warmer water and swifter currents prevail.