What Is a Hotspot? The Geology, Wi-Fi, and Everyday Meanings Explained

Short answer

• Hotspot has no single meaning, so the right answer depends on the sentence you are reading. In geology, a hotspot is a place where unusually hot material from deep inside Earth rises and melts through the crust to form a volcano, even far from the edge of a tectonic plate. Hawaii and Yellowstone are the two best known examples in the United States. In everyday technology, a Wi-Fi hotspot is a place, or a device, that lets other devices connect to the internet without wires. In conservation, a biodiversity hotspot is a region with many species found nowhere else that has also lost most of its original vegetation. The word is also used more loosely for a busy place, a trouble spot, or a place where something is concentrated. This article explains each meaning separately, starting with geology, the science meaning in this article's category, and then gives Wi-Fi the full treatment it deserves, since that is the meaning most readers meet in daily life.

By Emma Hudson

Which hotspot do you mean?

Use this table to jump to the meaning you need. Do not mix the rows together. A volcano hotspot and a Wi-Fi hotspot share a name and an idea, a concentrated source of something in one place, but they share nothing else.

If you mean	Go to	In one sentence
A volcano that forms in the middle of a plate	The geology hotspot below	Hot material rises from deep in the mantle, melts through the crust, and builds a volcano while the plate above slowly moves on.
Internet access without wires	The Wi-Fi hotspot section	A router, or a phone sharing its mobile connection, creates a local wireless network that other devices can join.
A region rich in unique species under threat	The biodiversity hotspot section	A region qualifies when it holds at least 1,500 plant species found nowhere else and has lost at least 70 percent of its original vegetation.
A busy place or a trouble spot	The other everyday uses section	The word is used figuratively for a place with a lot of activity, danger, or a concentration of some problem.

The geology hotspot: a volcano away from a plate edge

What a geology hotspot is

Most volcanoes form at the edges of tectonic plates, where one plate slides under another or where two plates pull apart. A hotspot volcano is the exception. It forms in the interior of a plate, far from those edges, because heat is coming up from below rather than from the plate boundary itself.

The United States National Park Service defines a hotspot as a large plume of hot mantle material rising from deep within Earth. As the plume rises, the hot mantle material partly melts, and that molten rock, called magma, rises through the crust and erupts at the surface. Encyclopaedia Britannica gives the same picture in shorter form: a hotspot is a region of Earth’s upper mantle that upwells to melt through the crust to form a volcanic feature. The key image is vertical. Something hot is rising from below. It is not the plate edge doing the work.

The United States Geological Survey explains the mechanism in the same way. A mantle plume is a region where Earth’s mantle is anomalously hot and buoyantly upwelling. As the hot mantle rises to shallower depths it causes melting, and that melting leads to a magmatic system that can produce volcanic eruptions. The plume stays mostly in place while the plate above it moves, and that combination is what makes hotspots so useful for reading Earth’s history.

How a hotspot track forms

Imagine a sheet of paper moving slowly over a candle flame. The flame stays in one place. Each new spot on the paper that passes over the flame gets scorched, and the scorched spots form a line. A hotspot track works in a similar way, and the National Park Service uses exactly this comparison, with a sheet of waxed paper moved slowly over a burning candle.

The process runs like this. First, hot mantle material rises and melts partway, and magma breaks through the crust to build a volcano above the hotspot. Second, the plate carries that volcano slowly away from the heat source, and cut off from fresh magma, the volcano goes extinct. Third, a new volcano forms over the hotspot in the crust that has now moved into position above it. Over millions of years, the result is a chain of volcanoes, islands, or seamounts, which are underwater mountains, with the active volcano at one end and progressively older, extinct volcanoes trailing away from it.

That age pattern is the fingerprint of a hotspot. Britannica states it plainly: the active volcanoes all lie at one end of the chain or ridge, and the ages of the islands or the ridge increase with their distance from those sites of volcanic activity. If a line of volcanoes gets older in one direction, a hotspot is a strong candidate explanation.

Hawaii: the ocean example

Hawaii is the classic hotspot example. The Hawaiian Islands sit near the center of the northern portion of the Pacific Plate, far from a plate boundary, yet they are volcanic islands. Britannica calls Hawaiian volcanoes the best examples of the hotspot type.

The United States Geological Survey gives the scale. The hotspot currently under Hawaii produced the Hawaiian Ridge-Emperor Seamount chain over the past 80 million years. Volcanoes in that chain get older the farther northwest you go from the Hawaiian Islands, with the oldest ancient Hawaiis off the coast of Kamchatka, Russia. The island chain you see today is only the youngest end of a much longer trail.

The National Park Service adds the picture: the Hawaiian Islands are broad and high at the southeast, becoming smaller and lower to the northwest. Haleakala on Maui and Hawaii Volcanoes on the Big Island represent different stages of passage over the hotspot. The Big Island, at the southeast end, is still over the heat source and still growing, while islands to the northwest have moved away from it, stopped growing, and are sinking and eroding.

Hawaiian eruptions also look different from many people’s image of a volcano. The Geological Survey notes that volcanic activity in Hawaii tends to build broad shield volcanoes like Mauna Loa, composed of numerous fluid lava flows. Hawaiian volcanoes erupt much more frequently than Yellowstone, typically producing fluid basalt lavas, but individual eruptions tend to be much smaller. The lava is runny, so it flows rather than exploding, and builds a broad, gently sloping shield instead of a steep cone.

Yellowstone: the continent example

Yellowstone shows what happens when the same process works under thick continental crust instead of thin oceanic crust. The National Park Service states that Yellowstone National Park contains the youngest of a chain of explosive volcanoes stretching across the Snake River Plain of Idaho to the Columbia Plateau in Oregon and Washington, where the Yellowstone Hotspot surfaced 17 million years ago.

The Geological Survey traces that chain in the other direction. Over the past 16 million years, the hotspot currently feeding Yellowstone caldera produced several caldera systems extending from McDermitt Caldera in southeastern Oregon and northern Nevada to Yellowstone caldera in northwest Wyoming. Each produced large explosive eruptions before plate motion carried it far enough away from the hotspot that access to the plume was cut off. The eastern Snake River Plain of southern Idaho marks this chain of ancient Yellowstones that gets older to the southwest from Yellowstone caldera. Note the direction: in Hawaii the trail gets older to the northwest, while in Yellowstone it gets older to the southwest, because the two plates move in different directions.

Why do the two systems behave so differently? The Geological Survey points to crust thickness as perhaps the most significant reason. Hawaii sits on oceanic crust about 10 kilometers, or about 6 miles, thick, while Yellowstone sits on continental crust about 45 kilometers, or about 28 miles, thick. Under Hawaii, magma rises quickly through thin crust and erupts as runny, low viscosity basaltic lava flows, with eruptions more frequent and smaller in volume. Under Yellowstone, thick crust blocks easy ascent, so magma stalls and accumulates, forming a large magmatic system that includes a rhyolite magma reservoir in the upper crust, at depths of 5 to 19 kilometers, or about 3 to 12 miles.

The surface signs at Yellowstone follow from that underground picture. Instead of tall shield volcanoes, Yellowstone forms large depressions called calderas, due to explosive eruptions of rhyolite magma, which later fill with viscous lava flows and domes. Its geysers, hot springs, and other hydrothermal features show that the hotspot is still alive, in the National Park Service’s words, and still heating groundwater from below.

What a hotspot is not

Three common confusions are worth clearing up.

First, a hotspot is not a plate boundary. Most volcanoes are related to subduction zones, where one plate slides under another, or to divergent margins, where magma ascends as crust is pulled apart. Hotspot volcanoes are the ones left over when those two explanations do not fit. Britannica puts the share in plain terms: the 5 percent of known world volcanoes not closely related to such plate margins are regarded as hotspot volcanoes. That figure comes from a Britannica article published in 2009, so treat it as an older reference estimate, not a freshly counted total. The logic survives any recount: hotspot is the explanation for volcanoes that plate boundaries cannot explain.

Second, a hotspot is not a single volcano. It is the heat source below, and the track it leaves behind. Hawaii is not the hotspot. The hotspot is the rising plume under the Big Island, and Hawaii, Maui, Oahu, and the older seamounts to the northwest are its products at different ages.

Third, a hotspot is not fixed forever in every detail. The standard picture describes plumes as mostly stationary while plates move above them, and scientists debate how deep particular plumes start and whether every proposed hotspot is really fed by a deep plume. This article describes the plume model as the dominant explanation for Hawaii and Yellowstone, which the Geological Survey supports, without claiming that every feature ever called a hotspot is equally proven. A list of dozens of hotspots should be read as candidates at different levels of confidence, not as equally proven plumes.

Why hotspots matter beyond volcanoes

Hotspots let geologists measure plate motion, because the age and direction of a hotspot track record how a plate has moved over millions of years. They also explain landscapes that plate boundaries alone cannot explain, such as volcanic islands in the middle of an ocean plate and explosive calderas far inland.

The Wi-Fi hotspot: internet access without wires

What a Wi-Fi hotspot is

A Wi-Fi hotspot is a physical location where people can obtain internet access, typically using Wi-Fi technology, through a wireless local area network using a router connected to an internet service provider. That working definition matches the Federal Communications Commission description of hot spots in public spaces like airports, coffee shops, and hotels.

There are two things the word can point to, and keeping them apart avoids most confusion. Sometimes hotspot means the place: a cafe, library, airport, or hotel that offers Wi-Fi. Sometimes it means the device or feature that creates the network: a phone’s personal hotspot, a portable hotspot device, or a router set up for guests. In “meet me at the hotspot,” it means the place. In “turn on your hotspot,” it means the feature on your phone.

Public hotspots: the cafe, hotel, and airport network

A public hotspot is created when a venue connects a wireless access point to the internet, usually through a router. Visitors in range can join that network with a laptop, tablet, or phone, and through it reach the internet. Some public hotspots are open: you join and you are online. Others are managed: you may need a password, a room number, a purchase, or agreement to terms on a login screen, often called a captive portal, before access is granted. Some venues limit speed or session length so one user cannot crowd out everyone else.

Public hotspots are found where people wait, work, or pass through: airports, bookstores, coffee shops, hotels, hospitals, libraries, restaurants, train stations, and schools and universities. Some libraries in the United States have also lent portable hotspot devices to patrons, extending access to people at home who lack in-home internet access or internet infrastructure.

Personal hotspots and tethering: your phone as the router

A personal hotspot turns a smartphone or tablet that has a mobile data plan into a small wireless router for other devices. The phone uses its mobile network connection to reach the internet, then shares that connection over Wi-Fi so a laptop or tablet can connect through it. This is often called tethering, although the two words are not exact synonyms. Tethering is the broader term for sharing a phone’s connection with another device, which can also happen over a USB cable or Bluetooth. Hotspotting usually means sharing over Wi-Fi specifically, with the phone acting as a wireless access point.

In practice, the steps are the same across most phones, although menu names differ by device. You switch on the personal hotspot feature, give the shared network a name and password, and then connect the other device to that network as you would to any Wi-Fi network. The connected devices share the phone’s mobile data allowance, so heavy laptop use, such as large downloads or video streaming, can consume data much faster than browsing on the phone alone. Some mobile plans include personal hotspot use, some limit it, and some charge extra, so your own plan terms matter more than any general statement here.

A personal hotspot is also a useful backup when home broadband fails or no public Wi-Fi is available. It is not a replacement for a home connection for sustained heavy use, because data allowances, battery drain, and signal strength all limit it.

How a Wi-Fi hotspot works, in plain terms

The process has four parts. First, something connects to the internet: a broadband line into a venue’s router, or a mobile network connection into a phone. Second, a wireless access point broadcasts a network name that nearby devices can see. Third, your device joins that network, usually with a password, and the access point passes your device’s traffic to the internet connection and back again. Fourth, the internet service provider carries that traffic to the websites and services you use.

Range is limited by design. Wi-Fi works over tens of meters indoors, not over kilometers, so a hotspot serves a room, a building, or a small outdoor area. Walls, distance, and the number of connected users all reduce speed, which is why a crowded airport hotspot can feel slow even when the underlying internet connection is fast.

Security is the part of the picture that most needs plain language. On an unsecured public network, information being transmitted can potentially be intercepted, as the Federal Communications Commission warns. Consumers should know whether they are using a secure, encrypted network or an unsecured network, and should be especially cautious about sending sensitive information over unsecured networks. The Commission’s consumer tips include using only fully encrypted sites, recognizable by https at the start of the web address and a lock icon, turning on a personal firewall, turning off the wireless connection when not using it, and using an encrypted virtual private network, or VPN, where appropriate. None of this makes a public network private. The strongest general protection on an unknown network is to avoid sending sensitive information, such as credit card numbers and passwords, over it at all.

A related caution is about network names. A network that looks like a venue’s official network may not be it, so confirming the exact network name with staff, rather than joining the strongest or most familiar looking signal, is a simple check that costs seconds. Devices that automatically rejoin known networks can also join a lookalike network without asking.

Public hotspot or personal hotspot: which to choose

The choice is usually practical. Use a public hotspot for free or convenient access in a venue when your task is not sensitive, such as reading the news. Use a personal hotspot when you need a connection you control, when no trustworthy public network is available, or when the task involves sensitive information. Use a home or office network for sustained heavy work and anything that needs stable speed over hours.

Other uses of hotspot

Biodiversity hotspots

A biodiversity hotspot is a conservation term with a strict definition, not a loose compliment for a pretty place. The United Nations Environment Programme World Conservation Monitoring Centre dataset states that there are 36 recognized biodiversity hotspots, described as Earth’s most biologically rich yet threatened terrestrial regions, and gives two strict criteria. First, an area must contain at least 1,500 species of vascular plants found nowhere else on Earth, known as endemic species. Second, it must have lost at least 70 percent of its primary native vegetation. Many hotspots exceed both criteria: the same dataset notes that the Sundaland Hotspot in Southeast Asia and the Tropical Andes Hotspot in South America each have about 15,000 endemic plant species, and that vegetation loss in some hotspots has reached 95 percent.

The concept was first defined in 1988 by scientist Norman Myers, and later adopted and developed by Conservation International, which introduced the quantitative thresholds. Treat the count of 36 as the figure in the 2016 dataset cited here, not as a number guaranteed to be current today. The durable part is the definition: a biodiversity hotspot must be both irreplaceable, because its endemic species live nowhere else, and threatened, because most of its original vegetation is already gone.

Trouble spots, busy places, and concentrations

In everyday language, hotspot often means a place where something is concentrated, whether that something is welcome or not. Oxford Advanced Learner’s Dictionary lists several of these uses: a place where fighting is common, especially for political reasons; a place with a particular type of danger or problem, illustrated by pollution hotspots; a place where there is a lot of activity or entertainment; and a place that is very hot and dry, where a fire has been burning or is likely to start. News reports use the same pattern for disease hotspots, where cases are concentrated in one city or region, and for crime hotspots, where incidents cluster in a small area. In each case the word adds the same idea: not just that something exists, but that it is concentrated here more than in the surrounding area.

Two specialist uses are worth one line each. In genetics teaching, a hotspot can mean a chromosome region where crossing over, the swapping of genetic material during reproduction, happens more often than average. In veterinary use, a hot spot can mean a moist, inflamed patch of skin on a dog or cat. Neither use is developed further here, and neither should be confused with the geology or Wi-Fi meanings.

How to tell which hotspot is meant

When the word appears without context, look for the company it keeps. Words like mantle, plume, volcano, plate, basalt, caldera, Hawaii, or Yellowstone point to geology. Words like Wi-Fi, router, password, tethering, data allowance, airport, cafe, or connect point to internet access. Words like endemic, species, vegetation, or conservation point to a biodiversity hotspot. Words like outbreak, cases, crime, pollution, or unrest point to a concentration of a problem. The sentence around the word almost always disambiguates it, even when the word alone does not.

Also note the full phrase. Geology and technology writing usually use the single word hotspot, while conservation writing uses the full phrase biodiversity hotspot. If you see biodiversity before hotspot, you are in conservation, not geology or Wi-Fi.

Frequently asked questions

Is a hotspot a volcano?

Not exactly. In geology, a hotspot is the heat source below the surface, a rising plume of hot mantle material. The volcano is what the hotspot builds, and the chain behind it is the hotspot track. Calling the volcano itself the hotspot is common shorthand, but the precise meaning is the plume and the place where it melts through the crust.

Are Hawaii and Yellowstone both hotspots?

Yes, and they are the two most instructive examples in the United States because they show the same process under different crust. Hawaii sits on thin oceanic crust and produces frequent, runny basalt flows that build broad shield volcanoes. Yellowstone sits on thick continental crust, where magma stalls and accumulates, producing explosive rhyolite eruptions, calderas, and geysers. Both are powered by mantle plumes that stay mostly stationary while their plates move above them.

How old is the Hawaiian hotspot track?

The hotspot currently under Hawaii produced the Hawaiian Ridge-Emperor Seamount chain over the past 80 million years, according to the United States Geological Survey. The islands you can visit are the youngest end of that chain, with volcanoes getting older to the northwest.

Is Yellowstone going to erupt soon?

This article makes no eruption prediction, and readers should be wary of any source that does. What can be said from the sources used here is that the Yellowstone hotspot is still active, as shown by its geysers and hot springs, and that its past eruptions have been large and infrequent compared with Hawaii’s frequent small eruptions. For current monitoring information, the United States Geological Survey’s Yellowstone Volcano Observatory is the authoritative source.

What is the difference between a Wi-Fi hotspot and tethering?

Tethering is the broader term for sharing a phone’s internet connection with another device, by Wi-Fi, USB cable, or Bluetooth. A personal hotspot usually means sharing over Wi-Fi specifically, with the phone acting as a wireless access point. A public hotspot, by contrast, is a venue’s network, not your phone’s connection.

Is public Wi-Fi safe?

Public Wi-Fi is convenient, not private. On a network you do not control, assume that other users and the network operator could potentially see unencrypted traffic. The Federal Communications Commission advises special caution about sending sensitive information over unsecured networks, and advises using fully encrypted sites, a personal firewall, and an encrypted VPN where appropriate. For sensitive tasks such as banking, your own mobile connection is generally the safer choice. No checklist makes a public network fully safe.

Does using a personal hotspot use up my mobile data?

Yes. Devices connected through a personal hotspot share the phone’s mobile data allowance, so laptop use can consume data much faster than phone browsing alone. Whether hotspot use is included, limited, or charged extra depends on your own plan.

What is a biodiversity hotspot?

A region that meets two strict criteria: at least 1,500 species of vascular plants found nowhere else on Earth, and loss of at least 70 percent of its original natural vegetation. The 2016 United Nations Environment Programme World Conservation Monitoring Centre dataset lists 36 such regions, including Sundaland and the Tropical Andes. The point of the label is conservation priority: unique life, already heavily threatened.

Why does one word have so many meanings?

Because the core idea travels well. In every use, a hotspot is a place where something is concentrated or intense: heat rising from the mantle, internet access in one location, unique species in one region, or a problem clustered in one area. The subjects differ completely, so the word alone never tells you which subject is meant. The surrounding words do.

Sources & references

• United States National Park Service. Hotspots, Geology. https://www.nps.gov/subjects/geology/plate-tectonics-hotspots.htm
• United States Geological Survey, Yellowstone Volcano Observatory. Yellowstone and Hawaii, how similar are they? http://www.usgs.gov/observatories/yvo/news/yellowstone-and-hawaii-how-similar-are-they
• Encyclopaedia Britannica. Hotspot, geology. https://www.britannica.com/science/hotspot-geology
• United Nations Environment Programme World Conservation Monitoring Centre. Biodiversity Hotspots, 2016 dataset. https://resources.unep-wcmc.org/products/124b9a66d1c642b5bc41d1ff703a0d21
• Federal Communications Commission. Consumer Tip Sheet, Wi-Fi Networks and Consumer Privacy. https://docs.fcc.gov/public/attachments/DOC-313634A1.pdf
• Oxford Advanced Learner's Dictionary. Hotspot, noun definition. https://www.oxfordlearnersdictionaries.com/us/definition/english/hotspot
• Wi-Fi hotspot, reference article, background for Wi-Fi hotspot types and locations. https://en.wikipedia.org/wiki/Wi-Fi_hotspot