I was watching G.I. Joe: Retaliation, and these government types taking a prisoner to an underground facility in a former East German mine shaft made some comment about how they'd gone so deep they were no longer technically in Germany and were now in international territory. Lunacy aside, are there international agreements on how deep someone's sovereign boundaries run? If someone runs a rail line 10 miles underground from London to Moscow, would the developers or governments have to get approval from all the countries they would go under? —Steve Selman
To review: What we have here is an admitted watcher of G.I. Joe movies suggesting that—"lunacy aside," mind you—one might plausibly dig a tunnel running the breadth of northern Europe without getting the surface dwellers on board. I'm not sure I have anything to add before we move on.
OK, backing up a bit: The accepted legal wisdom in the U.S. long held that property rights associated with a plot of land extended usque ad coelum et ad inferos: up to the heavens and down to hell, here meaning to the center of the earth. But, as I mentioned when explaining why you can't just shoot down planes flying over your house, the ad coelum part didn't survive the advent of aviation—the Supreme Court threw it out in 1946. And in a 2008 article, property-law professor John Sprankling argues that despite its continuing prevalence in American legal texts, the center-of-the-earth theory (we'll call it COTE) isn't actually the law either. His key conclusions:
1. There's no common-law basis for COTE—the English jurist William Blackstone pulled it out of his ass circa 1765.
2. More importantly, courts haven't actually ruled in a COTE-consistent manner: They'll generally uphold a landowner's subterranean rights near the surface, but "the deeper the dispute, the less likely courts are to recognize the surface owner's title."
3. At depths below the immediate subsurface but less than two miles down, court decisions and statutes have created so many exceptions to COTE that it can't really be considered a rule.
4. Whether the surface owner's rights go any deeper than two miles underground is something U.S. law has never established.
Subterranean property rights also vary depending on what you're trying to get at down there. Oil, flowing where it will, is governed in the U.S. under the "rule of capture," as admirers of Daniel Day-Lewis may remember: Anything you can produce from a vertically drilled well on your property is yours, even if it comes from underneath your neighbor's land. Mineral deposits are generally assumed to belong to the surface owner (unless the mineral rights have been sold separately), but here, too, there's a principle called extralateral rights, which can allow for mining parts of a vein that extend underground beyond a claim's surface boundaries.
International law hasn't spelled much of this out in any blanket fashion, and really it hasn't had to, as thus far few conflicts seem to have arisen from any ambiguity. In part, this may be because only a relatively small portion of earth's crude-oil reservoirs lie beneath international borders. One place where they do, though, is the Iraq-Kuwait border; a major point in the dispute that led to the 1991 Gulf War was Iraq's claim that Kuwait had used slant drilling to pump billions of dollars' worth of oil out of the Iraqi side of the field.
Sometimes the issue is figuring out where the borders are. A nation's territorial waters extend 12 nautical miles off its coast, but its exclusive economic zone, where it has rights to natural resources, go out 200 miles. Currently Russia, Canada, and Denmark (via Greenland) are each asserting that the Lomonosov Ridge in the Arctic Ocean is an extension of their respective continental shelves, thus expanding their EEZ to include potentially oil-laden stretches of Arctic floor that previously seemed pretty useless.
Recent developments in the energy industry may require refinement of underground law—a big one being fracking, where injected hydraulic fluid is used to break up subsurface rock and release oil and natural gas. When this fluid finds its way under neighboring property, the rule of capture butts up against the concept of subsurface trespass, which covers things like slant drilling; court rulings thus far haven't done much to sort it out.
Geologic sequestration—stowing captured CO2 emissions in underground cavities—raises some similar questions. To get the EPA's go-ahead, a would-be sequesterer has to show that the gas won't seep into the water supply, but issues of (e.g.) leakage into adjacent property currently have to be wrangled out under local law.
Anyway, in the absence of clearer guidance, it's safest to say yes, anyone who wants to run a 10-mile-deep railway tunnel from London to Moscow should at least get in touch with the Germans, Poles, et al. before making with the shovels. Oh, and also: At 10 miles, down the temperature will be about 750 degrees, so make sure that bar car has plenty of ice.
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