1986: River Border

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
River Border
I'm not a lawyer, but I believe zones like this are technically considered the high seas, so if you cut a pizza into a spiral there you could be charged with pieracy under marinaritime law.
Title text: I'm not a lawyer, but I believe zones like this are technically considered the high seas, so if you cut a pizza into a spiral there you could be charged with pieracy under marinaritime law.


Ponytail explains to Megan that the Missouri-Nebraska state border is based on the Missouri River they are watching. And because the path of rivers mostly only changes slowly, these borders are typically adopted to that changes. But then she explains that the river once had changed abruptly by a meander cutoff and the border didn't move with it. That means that they are on a part of the Missouri side of the river that in fact belongs to Nebraska.

It then occurred to Megan that she could break the law in this area because she is under the mistaken impression that she is in Nebraska but the police can't reach her over the river and Missourian cops actually don't have jurisdiction. In fact, there are no bridges linking it to Nebraska so police would have to go through Missouri in order to get to that part of Nebraska.

It should be noted that there are real-world examples of strange border interactions that either create legal loopholes or make law enforcement difficult. A famous example, in the US, is a section of Yellowstone National Park that crosses over the Idaho border. An article in the Georgetown Law Review noted that, since the Park is a federal district, and juries must be selected from people living in the same state and federal district as the crime, the only qualified jurors would have to live in the Idaho section of the park, but that section has no permanent residents. In theory, then, any crimes committed on this patch of land could not be prosecuted. How this would work out in real life remains questionable, as there are no records of anyone being arrested for a crime in that region, but the law seems to have inadvertently created a zone in which laws cannot be enforced. Similarly, Bir Tawil, a region along the border between Egypt and Sudan, is claimed by neither country as a result of the Halaib Triangle border dispute, and thus crimes committed in the area would be unlikely to be prosecuted. Megan seems to mistakenly think something similar is in effect any time a state's border briefly crosses a river.

The final panel shows Megan saying she's going to cut a pizza into a spiral, which while unconventional is by no means illegal, and she runs off to commit more things she calls crimes, likely similar acts to cutting a pizza in an uncommon way.

In the title text, Randall claims/hypothesizes the disputed region is probably considered like the high seas, suggesting the pizza case would then fall under maritime law. "Pieracy" is a portmanteau of pie (another name for a pizza) and "piracy"; and pizzas are frequently made with marinara sauce, so "Maritime" law is rendered "Marinaritime". This is most likely a reference to The Martian, in which it was noted that Mars is technically international waters as well.

The region mentioned in the comic can be seen here at Google maps and is known as McKissick Island. In 1904, the U.S. Supreme Court confirmed in Missouri v. Nebraska that a sudden change of a river's course does not change any border. See: Missouri v. Nebraska, 196 U.S. 23 (1904).

Riverine Boundaries in Common Law and Surveying[edit]

This strip is alluding to the concepts of 'accretion' and 'avulsion' in boundary law.

Accretion is the gradual change of the location of a river or stream by erosion or addition of sediment through natural river processes. According to common law in the United States and elsewhere, if a river or stream location changes gradually, then the boundary line moves with the stream. In cases of pure accretion, it is possible for a parcel of land to be entirely eroded away on one side of a river, and have material be added to the opposite side of the river. In such cases, one property owner could lose all their land.

An avulsion is a sudden change in the location of a river or stream, often due to flooding. In times of flood, a river can cut a new channel through surrounding land, which can create islands and oxbow lakes. According to common law, an avulsive change will not change the boundary of the land, as it is likely that the property is unchanged except for the new channel.

In the real world, however, river systems undergo both accretion and avulsion multiple times over a period of time. This makes the determination of property lines along riverine boundaries one of the most complicated aspects of boundary surveying. An examination of a river boundary will require in-depth research of the local history of the river, including reviewing deeds, government survey plats, private survey maps, aerial photos taken over time, local landowners recollections, and local lore. In situations where there is disagreement over whether an avulsive or accretive change happened, landowners may have to go to court for a suit to quiet title.

Further in-depth reading may be found in the US Bureau of Land Management's 2009 Manual of Surveying Instructions, Chapter 8, specifically pages 197-205. (See: PDF (37.7 MByte).)

Real-world examples[edit]

Often, borders defined by a river actually change. There are three methods to define a border:

  • The border follows one of the river banks, often in reference to a low-water mark. The exact location of the border is defined in a clear way - but one of the territories will lose terrain through erosion. When the river bends, erosion occurs at the outer bank and much less at the inner bank.
  • The border follows the middle of the river.
  • The most usual definition of a riverine border uses the talweg. The talweg (German for "valley path") always follows the line of the deepest points in the water body. Especially at river bends, the talweg is rarely in the middle of the river. Incidentally, the talweg also signifies the navigable zone of a river. In terms of natural borders, one counterpart of a talweg is the drainage divide, but these divides are hard to recognize on a map and rarely used to define a real border.

The Mexican-US-Border that follows the Rio Grande is one of the most prominent examples of an international border that needs meticulous regulation. Thus, the International Boundary and Water Commission was created. This commission was involved when the two nations rectified the course of the river, ceding equal amounts of land to each other. The Canada-US-Border is overseen by a similar commission. There is also a strange section on the border to Canada, which Randall mentions in this comic: 1902: State Borders.

The border between Delaware and New Jersey veers from the median and talweg methods such that Delaware's border includes all the way to the New Jersey shore where the Delaware River is within what is known as the Twelve-Mile Circle.

One of the causes of the Iran-Iraq War was the dispute on shipping rights on the Shatt-el Arab river, and because the border was defined as the low water mark at the eastern side of that river, Iranian shipping was severely restricted. So the Shah of Persia announced to ignore the 1937 treaty on shipping rights, saying that most riverine borders all around the world are defined by the talweg.

Between Switzerland and Italy, the border is, at most locations, defined by the actual drainage divide. Because the Theodul Glacier between Zermatt (Switzerland) and Breuil-Cervinia (Italy) is slowly melting, the drainage divide moves southwards, thus slowly enlarging the Swiss territory.

Most other national borders in Europe are defined today as fiat borders instead of following natural landmarks like rivers. If a river changes course now, the depicted situation would occur; however, most larger rivers have been rectified more than a century ago and thus don't change course often.


[Ponytail and Megan are standing on a grassy riverbank, with the nearby part of the river shown above their heads. They are looking towards the river and Ponytail is gesturing at the river with her hand.]
Ponytail: This is a cool spot.
Ponytail: The Missouri-Nebraska state line follows this river. If the river's path changes gradually, the border moves with it.
[A map is shown beneath the text spoken by Ponytail (off-panel). The map includes a bendy river shown in gray which is snaking its way from the left part of the panel down to the bottom. A dotted line indicates the old path of the river. It follows the gray river most of the way, but towards the bottom, this line moves away from the current river extending to north-east, including a large chunk of land that the river used to encompass previously. Two arrows point to the gray section of the river with the dotted line, and another arrow points to the section of the dotted line not following the gray section. Both are labeled. On each side of the dotted arc, where it is farthest from the gray part of the river the state names are labeled, so the text follows the direction of the river (almost north to south here).]
Ponytail (narrating): But when it abruptly changes course, the border stays behind.
Ponytail (narrating): This is a spot where that happened. We're on the Missouri side, but we're in Nebraska.
Old riverbed
[In a frame-less panel (with no background) Ponytail has turned to look at Megan who is holding a hand to her chin.]
Megan: Wow.
Megan: So...
Megan: We can commit all the crimes we want here and the cops can't do a thing!
[Megan runs away from Ponytail while she is holding her arm up in the air with a finger extended up.]
Ponytail: What? No. Why would you even think that?
Megan: I'm going to cut a pizza into a spiral!
Ponytail: That's not even illegal!
Megan: Crimes!

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


The title text doesn't have a typo. Barmar (talk) 16:06, 27 April 2018 (UTC)

"It then occurred to Megan that she could break Nebraska state laws and the police couldn't catch her (because the river was in the way)."

I think it might actually be because Megan is under the mistaken impression that it's neither Nebraskan nor Missourian territory, so neither set of cops actually have jurisdiction (similar to that thing where apparently there's an area of Yellowstone where no one has jurisdiction).
I believe you're right. The title text seems to confirm this. 20:03, 27 April 2018 (UTC)
While I saw the possibility of the Lawless Unclaimed Territory explanation (i.e. nobody has jurisdiction), I feel very sure the intended meaning is that the state that can get there has no jurisdiction and the state they're in can't get to them because of the river. (Mainly because Unclaimed Territory is a bit of a logical leap, while Cops Are Cut Off is fairly logical and somewhat true. Note the wording that "cops can't do a thing", not "there are no cops"). What amuses me is that I've heard of this location before AND that it is indeed true that there are no bridges, so it is indeed quite true that you can't reach this location from the rest of Nebraska. But of course I'm sure cops wouldn't hesitate to pass through Missouri. :) NiceGuy1 (talk) 04:01, 1 May 2018 (UTC)
Good thoughts! I was having a tough time wrapping my head around why the cops wouldn't just use a boat or helicopter, if necessary. That's why I didn't immediately consider it was the river stopping them. 14:36, 2 May 2018 (UTC)
I'd edit it myself, but I'm not entirely sure if I'm right. Thought I'd bring up the possibility so others could decide. -- 16:33, 27 April 2018 (UTC)
I fixed it. Grabadora304 (talk) -- Grabadora304 (talk) (please sign your comments with ~~~~)
I also read it as the river physically keeping the police out of the region so I added it back (before even reading these comments), but only as a second possibility, leaving the jurisdiction as the primary. Note that the river actually IS a physical barrier, there are no roads across the river there. -boB (talk) 21:07, 27 April 2018 (UTC)

This isn’t the only place in the US, or even in Nebraska, where this has happened. The town of Carter Lake, Iowa is only accessible by car by driving through Omaha. 17:08, 27 April 2018 (UTC)

The story of the similar situation on the Walloon (Belgian)-Dutch border, and the headless corpse. There used to be a situation like this on the border between Visé, Wallonia, Belgium; and Eijsden-Margraten in the Netherlands. The border used to follow the path of the river Maas/Meuse at the time of the Treaty of London of 1839. Between 1970 en 1979, the river was straightened, and until 2018, the border no longer followed the path of the river. That led to situations similar to the one in this comic on both sides of the river. Especially the Belgian bit at the Dutch side of the river became popular for drug dealings and illicit sexual escapades. At one time, a group of Antwerpians with moustaches proclaimed the area the independent Republic of Snorravia. In 2012, a headless corpse was discovered there. (I have heard that it was a suicide, though details are scarce.) That lead eventually to a land swap agreed in 2016–2017, effective January 1st, 2018. https://www.independent.co.uk/news/world/europe/belgium-netherlands-land-swap-agreement-river-meuse-borders-a7445751.htmlAdhemar (talk) 21:32, 27 April 2018 (UTC)

The Martian allusion - The joke about high seas, piracy, and maritime laws jumped out at me as echoing a joke made in The Martain, which we know is xkcd-approved. Does anyone else think that it's an intentional allusion? PvOberstein (talk) 23:45, 27 April 2018 (UTC)
How exactly can you commit suicide by beheading? -- Hkmaly (talk) 04:46, 28 April 2018 (UTC)
He could have committed suicide by slitting his throat, then something happened that caused his head to fall off. But who knows? Herobrine (talk) 07:30, 28 April 2018 (UTC)
Or by putting on the [Head of Vecna] Kazzie (talk) 05:48, 30 April 2018 (UTC)
A guillotine would be a handy device for a suicidal beheading. -boB (talk) 13:37, 30 April 2018 (UTC)

Wait, so, basically, two people buy plots of land with river flowing between them, after years the river changes course, and they go to court and hire experts to find why the river changed course and, depending on the outcome, one person can win a chunk of land the other person had paid for? And this is common in 21st century law systems? That's quite depressing. Jaalenja (talk) 09:44, 28 April 2018 (UTC)

...Except these aren't the property lines of people buying land, these are the borders of subsections of a country. If two people had bought land at this spot, one would now be on the other side (but would still live in Nebraska), the other just wouldn't have waterfront property any more (but would still have property in Missouri). NiceGuy1 (talk) 03:38, 1 May 2018 (UTC)
I was not talking about the comic itself, but about this part of the explanation
In cases of pure accretion, it is possible for a parcel of land to be entirely eroded away on one side of a river, and have material be added to the opposite side of the river. In such cases, one property owner could lose all their land.
In the real world, however, river systems undergo both accretion and avulsion multiple times over a period of time. This makes the determination of property lines along riverine boundaries one of the most complicated aspects of boundary surveying.
I am by no means expert, maybe it's just poorly worded explanation, but it certainly gave me the impression that something as arbitrary as the cause of a river changing course can affect whether or not someone gets to keep their land, which is by itself as absurd as the very fact they can lose land due to river changing course. Jaalenja (talk) 08:16, 3 May 2018 (UTC)
Jaalenja, you are correct in your reading of my text. A person can lose land due to a river or stream changing location, but since this is due to accretion/reliction, it happens very slowly, over decades. Year by year, a property on the outside of a bend of a river will be eroded by natural forces. Over decades of erosion it's possible to lose acres of land. Given enough time, it's conceivable that an entire property could be eroded, but that's pretty rare. Conversely, a property on the inner side of a bend can gain silt, then sand, then rocks, and eventually vegetation. The time scales that these occurrences happen are usually over generations, which is why most people don't worry about it.
Quick changes are the avulsive river movements, and in those cases, the property boundary doesn't change, because it was a sudden occurrence and the property didn't get destroyed in the process. It may seem like an odd system, but it has been held to be the most equitable way to deal with such natural forces by the English common law system and later on, the American legal system.Surveyorap (talk) 01:45, 23 May 2018 (UTC)

Congrats Randy, your title text made me claw my eyes out. Thankfully, I know kung-touch-typing-fu. 11:29, 28 April 2018 (UTC)

I removed the incomplete because I can't imagine how this explanation could be made any more complete than it is. In fact, this is one of most complete explains I've seen. Great job everybody! Gbisaga (talk) 18:15, 28 April 2018 (UTC)

I read the title text as a joke on 'pier'acy and 'marina'time law, as a freshwater-based set of puns rather than a pizza set. Phineas81707 (talk) 05:03, 6 June 2018 (UTC)

Can't believe there was no mention of Bir Tawil, the only habitable area on earth that isn't claimed by a country. It's basically exactly the scenario megan supposes to be happening in the comic (minus the river) - one country claims one border and the other country claims a different border so they both claim the same area, but the way the borders are drawn, Bir Tawil is claimed by neither country. Edited to add a mention. 04:42, 7 April 2021 (UTC)