Officially recognized as one of the toughest types of dirt in the nation

February 14, 2018 6:18 AM

"Scientists had speculated such a soil should exist but it had never been seen—until this discovery four years ago." The Wauneta duripan in northern Arizona is now "officially recognized as one of the toughest types of dirt in the nation." But how does the competition stack up?

The US Department of Agriculture (USDA) officially recognizes twelve different orders of soil. The USDA soil taxonomy is further divided into suborders, great groups, subgroups, families, and individual series. (24 mb PDF) What does that translate into? A lot of different types of dirt! (22 mb PDF) Many of these soils are easily penetrated by roots and shovels, and not worth mentioning here. Few are as tough as the mighty duripans, a heavy-duty soil horizon that can be as strong as concrete!

posted by compartment (34 comments total)

The state soil of Rhode Island is Narragansett Sandy Loam. Minnesota has Lester, while Wisconsin esrteems Antigo Silt Loam. That’s what I’ve got to bring to the discussion.
posted by GenjiandProust at 6:44 AM on February 14, 2018 [6 favorites]

I hadn't heard of "duripan" before this and don't know much about soil classifications, but I've seen hardpan several times that was so cemented that 300-class excavators hit total refusal and were completely unable to dig into it. It would have taken rock hammers to make any progress.
posted by Dip Flash at 6:54 AM on February 14, 2018 [2 favorites]

Dirt is fascinating stuff, and as a potter I know way too much about far too little of it. My personal favorites are Bethune Clay, which has massive amounts of iron oxide suspended in a clay matrix very similar to fire clay. I'm comes out of the ground mustard yellow and fires to a sweet potato oragne at cone six. Only problem is that it's very "short," meaning it has no ductility. Roll it into a snake and it'll crack apart under your fingers, even if it's sopping wet. A real challenge to throw with.

My other favorite was Albany Clay, which is usable staight out of the ground as a cone 6 glaze. Grind it up, wet it, put it on your pots and fire them. Boom, nice shiny uniform brown glaze. Add wood ashes to make it alkaline and it'll blow your mind with the insane textures it'll do. Potters (craft and industrial)all over the US used to use it in the first half of the 20th cenury. Could buy a 55 gallons n barrel of it for under a dollar, straight off the railroad car. Amazing stuff, too bad the mine that made it closed down years ago (I still have a small stash I hoard). We're still not sure what all was in it, something magic combined with deep slow grinding by glaciers and kept under pressure for thousands of years.

And that's just clays! Dirt is as local as is gets, it effects everything around and inside us and endlessly amazing... Except for that hardpan Georgia Red Clay in my back yard which is harder than cement in the summer and foul slime all spring and that I have to dig into to fix my fence. Fuck that stuff.
posted by 1f2frfbf at 7:14 AM on February 14, 2018 [22 favorites]

My other favorite was Albany Clay,

And down the rabbit hole I go...

The lands containing deposits of Albany slip clay are still undeveloped and covered by overgrowth. The site near Prospect Ave. and Livingston Ave. in Albany has been used as a landfill and contains the remains of the Empire Plaza site in Albany. The other mine site, across from North Lake Ave. near the Tivoli Lakes Wildlife Park (also in Albany), is overgrown with weeds.

I never knew that was at the end of the block where I live... I'm going to have to take a walk later.
posted by mikelieman at 8:01 AM on February 14, 2018 [4 favorites]

Not to abuse the edit, but this explains my backyard. Very, very much clay. I dread changing 4x4x8 fence posts.
posted by mikelieman at 8:02 AM on February 14, 2018 [1 favorite]

And here's another resource I just found.

http://www.nysm.nysed.gov/research-collections/geology/resources/hudson-river-lake-clay-exposures
posted by mikelieman at 8:03 AM on February 14, 2018

Yes! Keep these soil stories coming; I am loving them. Thanks to these comments, I now know that every state in the US has its own state soil!

Hardpan is fascinating stuff. Its presence is responsible for Lost Forest, a 5-square-mile ponderosa pine forest in the middle of the Oregon desert. An ancient lakebed underlies more recent soils, and traps groundwater at a level where the trees can reach it. The type of hardpan is called caliche, and I guess it acts as what hydrologists would call a confining unit. (Hydrologists and geologists, please hop in to correct me if I'm wrong or if I'm using terms incorrectly.)

Hardpan is also responsible dwarf forests, including those along the California and Oregon coasts.

And if you'll forgive me for sharing a sediment story instead of a soil story (although it's adjacent to the subject of state soils), I recently listened to a talk by a former orbiter project manager during Space Shuttle development in the 70s. According to the speaker, the raw material used to make the ceramic tiles was a sand from Minnesota called "gopher sand." I did a quick search to confirm that, but couldn't find anything else. 3M (Minnesota Mining and Manufacturing) developed one of the tile types used on the orbiter, so perhaps "gopher sand" was a bit of in-house jargon used to describe whatever 3M used as a raw source of silica.
posted by compartment at 8:12 AM on February 14, 2018 [4 favorites]

Fascinating! The state soil of South Carolina is the tidal marshland's Bohicket, which seems to me to be the official term for what the locals call Pluff Mud.
posted by Mr.Encyclopedia at 8:18 AM on February 14, 2018 [3 favorites]

Hardpan is evil. My old backyard was very sandy loam for the top four feet and then under that was hardpan (very similar to San Joaquin). Luckily I rarely had to go lower than four feet down for anything. But I also had crap for topsoil.

Now I live at the edge of the Great Basin Desert and the soil is specifically Oravada (I'm surrounded by alfalfa farms). It's very alkaline and when it gets wet it's very sticky, despite the good drainage. I keep forgetting about the sticky mud thing thing and I've ruined two pairs of slippers already.
posted by elsietheeel at 8:26 AM on February 14, 2018 [2 favorites]

And if you'll forgive me for sharing a sediment story instead of a soil story

Surely there should be a flag for “overly sedimental.”
posted by GenjiandProust at 8:32 AM on February 14, 2018 [16 favorites]

But is it tougher than Ajax?
posted by Greg_Ace at 8:33 AM on February 14, 2018

Hardpan is amazing and important! (Duripan is a type of hardpan). Hardpan soils are responsible for the formation of many California vernal pools--seasonal wetlands that form in hummocky terrain from winter rains that are trapped (in this case by a hardpan) and form a perched water table. Those pools are endemism hotspots that support tons of endangered species. The hardpans take hundreds of thousands of years to form, but in the past few decades we've figured out that we can totally destroy them with a D10 and a 4' shank plow. That deep ripping technology has been responsible for the orchard crop boom in the California central valley, but also represents irreversible loss of endangered species habitat. It is happening super fast, and the regulatory tools to fight it or mitigate it are not always effective.
posted by agentofselection at 8:55 AM on February 14, 2018 [5 favorites]

Those volcanic glass playas out in Nevada are hard enough to land experimental aircraft. I have been out on the Lunar Lakebed, if a rain comes up it immediately turns into a flat mirror, the water does not go down, it just starts a temporary lake until the evaporation takes it away. (As far as I can tell.) They are fun to drive on.
posted by Oyéah at 8:56 AM on February 14, 2018 [1 favorite]

About a year ago I hand-dug about 50 fence post holes on a property out near Sequim, which is on the north side of the Olympics in western Washington. I've dug some holes in grounds before, including a stint working with a geologist that usually involved putting about a ton of hardpan and rocks into big plastic totes.

The soil out by Sequim was something entirely different. I was expecting a ton of hard, back-breaking work and lots of glacial rocks and gravel, but, no. This soil was like red velvet chocolate cake. I've cut bread that was tougher than this.

Digging in it was a sheer joy. Heavy loam and crumb, slightly sandy and just a touch of clay to hold it all together. So much macro and micro POM you could practically eat it as a salad. Putting a shovel to it was less force and digging and more simply cutting out a shovel full of heavy cake-like dirt to lift out of the hole.

I was disappointed when I ran out of holes to dig because it was just that satisfying to dig in. Because we had so much extra time on the project since the concrete truck wasn't due on site for another two days, I remember going back over all the holes and getting the sidewalls cut and shaped as perfectly cylindrical as possible. When I was done it looked like someone had come along with a cookie cutter and punched out a nearly identical row of holes 200 feet long in bright green grass. If they were square holes it would have looked like a Minecraft render.

I've since had vivid and strangely satisfying dreams about that dirt. Digging in it. Flaking it apart with my bare hands. Growing things in it.
posted by loquacious at 9:48 AM on February 14, 2018 [15 favorites]

The soil maps the USDA puts together are GORGEOUS. I have a six-foot tall soil map of Illinois (huge slow-loading jpeg) that I'm just waiting for the right wall to hang it on. They're immediately intriguing because they sort-of look like a geographical map of your state as you're familiar with it (since much of the soil follows geographical features like mountains or rivers or glaciated depressions), but it's obvious it isn't quite that.

(You want the General Soil Map of $state, which includes lots and lots of colors, not the ones that map soil orders (not as many colors) or that map drainage or whatever. They can be a little tricky to find since they're only put out like once every 60 years or so, on a rotating per-state basis, so lots of them haven't been digitized and don't necessarily turn up on the "online resources" your state geological survey has online, which is probably more up-to-date information useful to farmers and construction concerns.)
posted by Eyebrows McGee at 10:29 AM on February 14, 2018 [7 favorites]

If dirt is as hard as a rock, what makes it dirt instead of rock?
posted by clawsoon at 10:48 AM on February 14, 2018 [2 favorites]

They are fun to drive on.

Is it really driving when you can basically point the car in any given direction, take your hands off the wheel, close your eyes and floor it for 10 minutes?

Do not do this. This is how you find the one rut in a few square miles and flip at 50mph.
posted by loquacious at 10:49 AM on February 14, 2018 [2 favorites]

If dirt is as hard as a rock, what makes it dirt instead of rock?

Solubility. Does it dissolve or turn to mud when it gets wet?

There are sandstones you can crumble with your hands, but they won't readily dissolve in water. Soak a hard pan with water long enough and it absorbs the water and will turn into mud or clay.
posted by loquacious at 10:51 AM on February 14, 2018 [5 favorites]

If dirt is as hard as a rock, what makes it dirt instead of rock?

After some searching, I would say that perhaps hardpan/duripan is both dirt and rock, or perhaps occupies a taxonomic space between "stuff that is very clearly a rock" and "stuff that is very clearly dirt." Caliche is soil that's cemented together with calcium carbonate. The calcium carbonate is there because it precipitated out of a water source. Travertine and tufa are more pure forms of calcium carbonate build-up. I think most geologists would consider travertine and tufa to be rocks. Caliche seems to me like a rock with some dirt in it. Maybe geologists would call it a rock, and soil scientists would call it a soil. I'm not sure.

My impression was that most hardpans are insoluble for the same reasons they are impermeable. On the flipside, limestones (composed mainly of calcium carbonate) are also somewhat soluble over long timeframes. Think of karst formations that cause sinkholes in Florida. Halite (rock salt) is considered a chemical sedimentary rock. Whether a mineral precipitates or dissolves can depend on local conditions (e.g., pH, how much of the stuff is already in the water).

My experience with geologic definitions is that the taxonomic bounds are seldom clear cut. (When does a rill stop being a rill and start being a gully? When does a gully become a canyon? Or a valley?) If someone more knowledgable than me could drop in here and explain if there's something like an international geological standards body that sets definitions, that would be helpful!
posted by compartment at 11:38 AM on February 14, 2018

Yes, iron-silicate durpian (the one I'm intimately familiar with) is quite insoluble--it is a precipitate. Soil scientists claim it as a soil because it formed through standard soil formation processes. Soils are very generally divided into the O Horizon--surface organics, A horizon--zone of leaching, B horizon--zone of deposition, C Horizon--mineral parent material, and then underlying bedrock. Duripan is a hypertrophied B-horizon, not bedrock or mineral parent material. Geologists might claim it as a rock, but for soil scientists it is a soil.
posted by agentofselection at 11:54 AM on February 14, 2018 [1 favorite]

agentofselection: Soil scientists claim it as a soil because it formed through standard soil formation processes.

How do standard soil formation processes differ from standard rock formation processes?
posted by clawsoon at 11:58 AM on February 14, 2018

I'm not a geologist, (where is Barchan when you need her?), I'm an ecologist rapidly getting out of his depth, so I'm likely to speak in generalities so broad as to be inaccurate. So let's do it! Rocks are formed as either igneous rock--minerals melted down deep in the earth and then cooled; as metamorphic rock--one type of rock transformed into another by heat and pressure; or sedimentary rock--minerals weathered into small pieces, then re-consolidated back into a solid mass. Sedimentary rock is kind of similar to duripan in that they both involve weathered materials being re-consolidated. Sedimentary rock is usually re-consolidated by the pressure of being deep underwater or deep underground, though. Duripan is cemented by the precipitation of insoluble chemicals from aqueous solution. Also, soils, by definition, are formed in terrestrial environments and with the involvement of biological processes such as weathering by microorganisms, input of organic materials, and agitation by plant roots and burrowing animals. Sometimes living things contribute to or cause the formation of rocks (e.g. limestone), but they are not a required participant.
posted by agentofselection at 1:05 PM on February 14, 2018 [2 favorites]

Soil formation includes and supports biological processes.
posted by clew at 1:05 PM on February 14, 2018

From Keys to Soil Taxonomy, 10th ed (the US authority):

Soil in this text is a natural body comprised of solids (mineral and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the original material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment. This definition is expanded from the 1975 version of Soil Taxonomy to include soils in areas of Antarctica where pedogenesis occurs but where the climate is too harsh to support the higher life forms.

So, not even necessarily biology; can be interaction with climate. In fact, there's probably a vigorous fight going on to decide if Mars has soil.

The five factors of soil formation are climate, organisms, relief, parent material, and time.
posted by clew at 1:10 PM on February 14, 2018 [3 favorites]

This is more complicated than I expected.
posted by clawsoon at 1:29 PM on February 14, 2018 [1 favorite]

Not to abuse the edit, but this explains my backyard. Very, very much clay. I dread changing 4x4x8 fence posts.

If you can hold off changing your posts for a couple of years, get a thick layer of woodchips down and let mother nature take care of the rest.
posted by turbid dahlia at 2:14 PM on February 14, 2018

Mars planetary scientists are (mostly? sometimes? while they must?) using particle size:

“rocks” generally refer to 10 cm scale and larger materials (e.g., fragments, breccia, and exposed outcrops) that have high thermal inertia, have areal fractions consistent with the Viking Infrared Thermal Mapper (IRTM) data [e.g., Christensen, 1986; Golombek et al., 2005], and are immobile under current eolian conditions. [...] “Soil” refers to all other, typically unconsolidated, material including those sufficiently fine-grained to be mobilized by wind [e.g., Banin et al., 1992; Jerolmack et al., 2006]. Soil consequently encompasses a variety of regolith components identified at the five landing sites. Typical examples are: bedform armor, clasts, concretions, drift, dust, rocky fragments, sand, and soil [e.g., Fergason et al., 2006; Golombek et al., 2005; Sullivan et al., 2005; Yen et al., 2005].

Karunatillake et al., 2003.

More explicit about modification in place -- but I don't have access to the article so I don't know what they're counting --

Now that space exploration has greatly expanded our understanding of the Solar System, providing consistent evidences that the loose, unconsolidated "skin" of some nearby rocky bodies is lifeless, it is time to establish if the latter can be considered to be soil in a pedological sense. Our feeling is that, since the concept of soil chiefly bases on the occurrence of weathering and internal differentiation – both induced by biotic and/or abiotic processes – in an incoherent mass of mineral matter, the clearly altered surfaces of Venus, Mars, and our moon deserve the rank of soils.

Certini & Scalenghe, 2007.
posted by clew at 2:15 PM on February 14, 2018 [4 favorites]

if there's something like an international geological standards body that sets definitions, that would be helpful!
World reference base for soil resources 2014
International soil classification system for naming soils and creating legends for soil maps - Update 2015
posted by unliteral at 4:50 PM on February 14, 2018 [1 favorite]

Looking at that definition of soil, I'm wondering what substance there is that fulfills all the qualifications for soil - except that it doesn't occupy any space.
posted by moonmilk at 5:05 PM on February 14, 2018 [1 favorite]

The Keys to Soil Horizons definition seems broad enough to include rock layers (if not as a soil type, then at least as a soil horizon). I'm looking at the 12th edition, which goes on after the definition to somewhat acknowledge that the question "is this material part of a soil?" does not always have a clear answer: "The lower boundary that separates soil from the nonsoil underneath is most difficult to define."

"Nothing too deep" seems to be an important part of the working definition of soil. The text goes on to state: "For the practicality of soil survey, the lower boundary of soil is arbitrarily set at 200 cm. In soils where either biological activity or current pedogenic processes extend to depths greater than 200 cm, the lower limit of the soil for classification purposes is still 200 cm."

The World Reference Base for Soil Resources 2014, update 2015 (hello, clunky title) uses an even more expansive definition:

Although there are good arguments to limit soil survey and mapping to identifiable stable soil areas with a certain thickness, the WRB has taken the more comprehensive approach to name any object forming part of the epiderm of the earth ... Therefore, the object classified in the WRB is: any material within 2 m of the Earth’s surface that is in contact with the atmosphere, excluding living organisms, areas with continuous ice not covered by other material, and water bodies deeper than 2 m ... The definition includes continuous rock, paved urban soils, soils of industrial areas, cave soils as well as subaqueous soils."

The 2015 Reference Base contrasts this with the definition from the 1998 version of the text, which is not nearly as expansive, and requires both mineral and organic constituents to be present.

The definitions of soil in current use are a bit like the Commerce Clause of the Soil Constitution. Almost everything on Earth's surface is a soil, and is subject to the authority of soil scientists! Rocks can be soil!
posted by compartment at 8:46 PM on February 14, 2018

And next time you think about how big Australia is, and how few people we have here, think about duripan soils. We have areas the size of US states dominated by the stuff.
posted by Thella at 11:32 PM on February 14, 2018

Rocks *will* be soil, as soon as they've emerged to be looked at. The smallest atmospheric weathering, the least haze of lichen, and they're on their way.

From a geological time-perspective, that's all right, as soil will also be rocks again. (Except for the nitrogen, says the atmosphere: that comes back to N_2.)
posted by clew at 11:46 PM on February 14, 2018

Metafilter :"This is more complicated than I expected."
posted by Mitheral at 1:39 AM on February 15, 2018 [3 favorites]

I couldn't resist making a question about the definition of soil that occupies space.
posted by moonmilk at 2:32 PM on February 15, 2018