There are still people looking into the caverns of Mars, for a safe HAB. Seal them off and build a sustainable atmosphere within. This answer comes up all the time. Musk is even considering it for the long term .
Some of the thoughts in here aren't up with paradigm change, economics for a starter, payload of 100 tons instead of 1 ton, that it's a private company with deep pockets doing it privately rather than a NASA mission and that it's not a one way mission that we used to think it was, so I'll have a go.
Financing is coming out of SpaceX, rather than NASA handing out money and it makes quite a difference. The NASA way doesn't happen as it is too expensive and all the rentseekers will leverage every last cent. SpaceX is building Starship without a NASA contract to do it (though it is subsequently providing a variant for the Artemis program). Some billionaires buy big yachts, this just happens to be Elon's version of a big yacht, ie something to do with the money that he finds meaningful. He is coming at this after a lot of lessons learned about high tech manufacturing, bleeding edge research and specifically, mass production and those lessons are coming into SpaceX, the speed at which they've been building prototypes at Boca Chica is astonishing. By comparison, the divisions of major manufacturing companies engaged in space aren't doing it as mass production, such as their airplanes, but it seems like after all these decades they still do it all bespoke.
The economics perception most people have about space colonisation is based on past endeavours. Space was expensive, that precious rocket or 2 and payloads for your venus probe or flag planting on the moon, was made harder and more expensive with the most cutting edge of everything to try and ensure success. So much unobtainium went into it, difficult/one off, extreme and barely tested materials and processes without a manufacturing base for it in existance and factoring in the rent seekers that made a fortune out of NASA and the military. What you all need to get your head around is Starship. A transformed space industry is Space Shuttle flying on average, 2.6 flights/year at $54,000/kg to orbit, to Falcon flying 1/month at $2700/kg to Starship at $10/kg, but mindbogglingly, they are aiming to manufacture starship at 1/week and (rapidly) reusable at that, which will mean many launches daily for cheap (not all bound for Mars). Yes that is an ambit claim by Spacex, how many they can build and the actual launch cost are yet to be proven. I've bought guitars online from Japan, I wish that I could get them via sea freight, let alone airfreight at $10/kg to Australia. To send 100 tons at a time (relatively cheaply) and with a fleet, instead of 1 ship with 2-3 astronauts and a measly 1 ton of cargo is a radical change from the 70s concept.
The key to paradigm change? Willingness to use good old fashioned steel instead of cutting edge materials and other common, well understood materials coupled with mass scale production processes instead of building unique items. Turned from an incredible science/engineering project that space was, into a mass manufacturing/engineering project. It is by comparison, going to a local engineering shop and getting them to design and make 1 car for me (which would cost a fortune) to buying a mass produced car. Similarly, the colonies themselves, if NASA made them, the entire habitat would be shipped from earth with the plumbing made from platinum (for reasons), after a suitable nanomaterial was devised for a chair in the loungeroom after a 10 year, 500 people research initiative involving 300 high tech companies and collaboration with international subcomittees on colour choice, chair height, east or west facing etc. The paradigm change will see them living out of Starship while they build the initial base out of an amount of material sent ahead, but will produce as much as possible out of locally avialable material. The space station has it's food and water sent up and the cost per meal is thousands, Mars will make it's own food and water. The cost per head for a trip to Mars according to one Musk soundbite was an intention to get it to a few hundred thousand dollars, for perspective the median house price in Australia is $693,000 usd. Sure, it is expensive, but not necessarily out of reach and fundible by proffesional individuals rather than the 1950s to 1970s concepts of manned missions to Mars which would bankrupt even the biggest world economies.
That reusable rocket will see Starships returning, empty or full, instead of having it's one use (meaning that it's only good for recycling at the destination). Even though the window to return is every 2 years, that you can return is radically different to it being a one way mission and is a difference in peoples inclination to go. Materials returning don't need to be booked at the full cost of a one way rocket from Mars to Earth.
The fundamental of why Mars vs elsewhere (aside from mother Earth).
It has the required, easy to get basic resources that let you resupply for the return trip. e.g. CO2 etc in the atmosphere, Water present in numerous places, means you can make the resources required for a return trip (fuel, oxidiser, food) which is why SpaceX is focussed on methane engines for Starship.
Those same basic resources of Carbon, Hydrogen and Oxygen let you make so many things, foods (proteins, fats, carbohydrates), plastics, petrochemicals, graphene/graphite. In instances, amounts of other elements are needed for variant compounds, but Mars has those too. When you do need specific things that organic chemistry won't let you do, such as a conductor for electronics (copper, silver etc), or Steel for construction and manufacturing, Mars has iron, carbon, chrome, vanadium, tungsten etc. But for the main part of construction and manufacturing, I think they'll get by quite simply with plastics and crushed rock (cement, bricks, concrete) for bulk building material plus conducting material, it will be made cheap and easy instead of the most advanced futuristic build, though that does not mean it has to be stone age living conditions.
Why would people go?
I've lived in multiple cities without a go home factor, home is where you make it, it's about why the destination is attractive. If you were an engineer, there are new challenges, almost any discipline of science would have people wanting new challenges, from the obvious in geology and vulcanology, to biologists researching foodcrops, new challenges for human bodies for medical, sports, new challenges for material sciences in different conditions (lower gravity etc). Also, people just needing a job, there will be opportunities for bartenders, service workers, farmers, miners etc. With the Starship program, ships will be returning be it empty or full, it's not like being sent for life to a penal colony, you aren't stuck - though you just can't immediately return on a whimsy.
That is a more specific and contemporary "why", but the same old "why" of migration still exists. How many religious colonies have been setup (oodles), ethnic migrations (oodles), opportunistic (from vikings settling the Faroe Islands, Iceland, Greenland, North America, Migrants from Europe to the colonies etc... Oodles). That's the people who want to go, then there are the people who will be sent, with Geopolitics on Earth being a thing, China, the States, India, Russia and others will vie for strategic positioning and send their soldiers, scientists and support staff.
Finally, it is not futuristic or fantastic, it is in progress now - the Artemis project by Nasa is about a permanent moonbase this decade and vast sums have already been spent, with the first launches to kickstart it off happening soon. Settling space is not the fantasy that it once was, but an active work in progress. It's just that, where NASA is focussed on the Moon, private industry (Spacex) is focussed on Mars and there is some crossover between the two.
So, Yellowstone would be a good chance of that happening. It wouldn't take much to set it off. Geologists have been expecting that for decades.But Mars became messed up either way. Water over eons forms caves and caverns. And Mars does have those. Looking for water ? Look in the caverns.
Carlsbad Caverns. they had to cement up the spring that once flowed through there . To make it a tourist attraction.
I've been telling people this for years. Living on Mars will be impossible. Living INSIDE Mars would be totally doable. We would need to build numerous tunnel boring machines and then build deep climate controlled chambers with hydroponic gardening facilities to grow food and produce O2 for the colonists. With Mars being basically tectonicaly dead the size and scope of the underground dwellings we could build will be limitless.The suggestion that humans will soon set up bustling, long-lasting colonies on Mars is something many of us take for granted. What this lofty vision fails to appreciate, however, are the monumental—if not intractable—challenges awaiting colonists who want to permanently live on Mars. Unless we radically adapt our brains and bodies to the harsh Martian environment (become cyborgs), the Red Planet will forever remain off limits to humans.
Mars is the closest thing we have to Earth in the entire solar system, and that’s not saying much.
The Red Planet is a cold, dead place, with an atmosphere about 100 times thinner than Earth’s. The paltry amount of air that does exist on Mars is primarily composed of noxious carbon dioxide, which does little to protect the surface from the Sun’s harmful rays. Air pressure on Mars is very low; at 600 Pascals, it’s only about 0.6 percent that of Earth. You might as well be exposed to the vacuum of space, resulting in a severe form of the bends—including ruptured lungs, dangerously swollen skin and body tissue, and ultimately death. The thin atmosphere also means that heat cannot be retained at the surface. The average temperature on Mars is -81 degrees Fahrenheit (-63 degrees Celsius), with temperatures dropping as low as -195 degrees F (-126 degrees C). By contrast, the coldest temperature ever recorded on Earth was at Vostok Station in Antarctica, at -128 degrees F (-89 degrees C) on June 23, 1982. Once temperatures get below the -40 degrees F/C mark, people who aren’t properly dressed for the occasion can expect hypothermia to set in within about five to seven minutes.
The notion that we’ll soon set up colonies inhabited by hundreds or thousands of people is pure nonsense.
Mars also has less mass than is typically appreciated. Gravity on the Red Planet is 0.375 that of Earth’s, which means a 180-pound person on Earth would weigh a scant 68 pounds on Mars. While that might sound appealing, this low-gravity environment would likely wreak havoc to human health in the long term, and possibly have negative impacts on human fertility.
Yet despite these and a plethora of other issues, there’s this popular idea floating around that we’ll soon be able to set up colonies on Mars with ease. SpaceX CEO Elon Musk is projecting colonies on Mars as early as the 2050s, while astrobiologist Lewis Darnell, a professor at the University of Westminster, has offered a more modest estimate, saying it’ll be about 50 to 100 years before “substantial numbers of people have moved to Mars to live in self-sustaining towns.” The United Arab Emirates is aiming to build a Martian city of 600,000 occupants by 2117, in one of the more ambitious visions of the future.
Even if all these obvious problems are somehow solved, who in their right mind (after the initial kick of living on another planet wears off) would actually wanna live in such a hellish place?
And what about the critically important microbiome?
Apparently, many people have forgotten the Biosphere I and Biosphere II projects in the Arizona desert designed to test a completely enclosed, self-sustaining environment for long space flights. After ten of millions of dollars spent, both were miserable failures.
We could still build massive "solar farms" on the surface, and transfer the energy below. Also they've nearly perfected small modular nuclear reactors. (Pocket Reactors) So underground "grow lights" will be easily provided for.Sounds good, but don't forget sunlight for photosynthesis, unless you want to live on mushrooms.