• AIR OASIS: on a thin-aired world like Tharn, TRENCHES and the deepest CRATERS essentially form a second, separate ecology nothing like the surface. The air is much thicker--in the deepest trenches, over twice as dense--holding in moisture, blocking radiation. Air-oases are also the only place large creatures can fly. Life may have originated here, and fully half of all Tharnian species live in these narrow oases. They're Tharn's biological hot spots--its coral reefs.
• ARC BASIN: a basin on the edge of an UPLAND, ringed entirely by mountains associated with a TRENCH; the geological equivalent of our coastal seas sheltered by island arcs, like the Caribbean, Bering, and China Seas. Cut off from rain by the surrounding ranges, Tharnian ARC BASINS are usually harsh deserts, though some have shallow lakes along the margins. Earth has only one rough equivalent: the dry Tarim Basin of central Asia.
• ARC RANGE: many of the uplands analogous to our continents extend curving mountain ranges, often with trenches at their feet. They're precisely like our island arcs--just subtract water! Well, not quite ALL water: the mountains' outer slopes often wring moisture from Tharn's stingy winds, and sustain forests; their snows feed TRENCHLAKES at their feet. The inner slopes are usually drier and drop to deserts in the ARC BASINS below.
• ARTHO: an odd moth-bat-monkey-cat unique to Har Trench. One of the 13 intelligent species on Tharn. See Peoples for chart.
• BASALT: dark, heavy, iron-rich volcanic rocks underlying sea-beds on Earth. Contrasts with lighter sedimentary and metamorphic rocks common on continents, like granite and limestone. On Tharn, wide basaltic plains called BEDS are common.
• BASIN = any BED forming a single drainage, whether it's a larger river or a BEDSEA. Since Tharn's land is continuous, BASIN, SHORE and NECK are the common divisions.
• BED, BED-PLAIN: a mid-altitude basaltic plain--what we'd call seabed, though on Tharn they're mostly dry. The closest planetological term is "planitia", but that implies low plains, and BED specifically means the middle of the three basic land-levels: TRENCHES, BEDS, and UPLANDS.
• BEDLAKE, BEDSEA: a shallow sea, often island-dotted, out on the BED, the mid-level plains analogous to seabed on Earth. Bedlakes over 100,000 sq km can legitimately be called seas. They average less than 50 meters deep, so light penetrates to the bottom, feeding "coral" reefs. Over time, as plates slide along under rainbelts, bedseas crawl across the bed like huge amoebas. On flats, they resemble shallow desert seas like the Aral, or Lake Chad; in hilly terrain, Ice Age lakes like Lahontan or Bonneville--rugged mazes of land and water. The biggest is a million square kilometers.
• BEDLEVEL: see DATUM.
• BIRDSEA: a peculiar hybrid sea, formed by the merging of the two basic types of lake on Tharn: a shallow, wide, irregular BEDLAKE and a long, deep, narrow TRENCHLAKE. Such merged seas typically look like birds, with a narrow trenchlake body and wide bedlake wings. Birdseas are by far the deepest on Tharn, since the trench fills to the brim. The formation of even a few birdseas can sequester much of the world's water--a climatic catastrophe initiating a DRY AGE.
• BO: a scaly bipedal mammal, One of the 13 intelligent species on Tharn. See Peoples for chart.
• CALDERA: a large volcanic crater. Many have overlapping vents, so various cliff-walled pits of different depths combine into complex shapes. Lakes often fill the floors.
• CAMAROO: a bipedal, fluffy cameloid tolerant of high altitude, widely distributed and managing most caravans. One of the 13 intelligent species on Tharn. See Peoples for chart.
• CENTAH: a feline centauroid of the equatorial veldt; one of the 13 intelligent species on Tharn. See Peoples for chart.
• CHAOS: a rugged, violently disordered region with no drainage pattern. A large chaos exists on Mercury opposite the Caloris Basin, and Tharn has one for exactly the same reason. Tharn suffered a huge impact 3-400 million years ago. Shockwaves spread around the world, and then (as if Tharn were a great lens) converged again on the far side, where Himalayan peaks leapt from the ground in an instant, creating chaos--a jumble of gigantic peaks and dead-end basins. By now it's eroded down from Martian to merely Alpine heights, and rivers have penetrated the eastern side, but most of its drainages are still internal.
• CHASMA: a winding groove walled by twin ridges, often quite high and steep, where crust is spreading. On Earth, most are submarine, but the rift valleys of East Africa, with their long lakes, are quite Tharnian. Volcanoes tend to flank the rifts, especially where they bend or fork. Chasma is the standard planetological term, but I often use RIFT instead, to emphasize the parallel with Terran geology.
• CHONG-MA: a midsummer song-festival held by mamooks. A loud, raucous event, part fair, part singles bar: both sexes (indistinguishable to non-mamooks) sing "songduels" to gain status and impress potential mates. Songs are usually narrative, always from dreams (or at least pretend to be) and are judged as much on their humor and psychological insight as on beauty of music and voice.
• CORONA: a round or oval blister, sometimes bulging, sometimes sagging, sometimes popped--occasionally a smooth dome but usually with concentric ridges and rifts. Coronas are big--from 100 to 1000 or more km across. They're probably upwellings from the mantle, but just possibly down-wellings that pull surface stuff together, or a small, rotating buffer zone between larger shifting plates--a sort of bearing to reduce friction. Venus has many coronas, Earth none, and Tharn a few, like the Madhu Hills of central Barsoom, the Notan Hills south of Dejah Upland, and Yakkakee Ring east of Dejah.
• CRATER: always an impact crater, not volcanic (see CALDERA). Because Tharn's air is so thin and erosion is a bit slower (especially in the uplands), more small craters survive than on Earth. Low gravity means they're generally deeper than on Earth, too; the sunken floor of a large crater can be an AIR OASIS.
• DATUM: an altitude of zero. Tharn has no worldwide sea, and hence no "sea level", so Tharn's zero is just the average height of the BED-PLAINS, the equivalents of our seabeds; thus, datum is sometimes called BEDLEVEL. The TRENCHES drop 2-7 km below datum, and the UPLANDS (tectonic equivalents of our continents) are 5-7 km high, with peaks rising to 16 km (Everest rises 11-12 km above our abyssal plains). Tharn's highest peaks are Martian-scale shield volcanoes rising 15-18 km above datum. On Tharn, altitude matters. At datum, air pressure is only 0.24 Earth atmospheres, equivalent to the top of Everest. In the TRENCH OASES it rises as high as 0.4-0.5 atmospheres (merely Alpine). Pressure in the UPLANDS averages 0.1 atmospheres. Harsh though this sounds, even the mountaintops still have many times the pressure on Mars! There's thin... and thin.
• DEBRIS APRON: see SPLASH APRON and RAYS
• DORSA, DORSAE: a long straight ridge. Dorsae often mark a fault where tectonic plates slip laterally but also squeeze. The Indian Ocean's "Ninety East Ridge" is the best Terran example; compare to Tharn's Yola Ridge in northeast Barsoom Basin or Chornis Ridge north of Tarkas Upland. Fields of smaller dorsae are often compression features, as in central Thuvia around the Dzel Lakes.
• DRY AGE: Earth regularly slides in and out of ice ages. Tharn irregularly slips in and out of dry ages. Whenever a deep trench gets in a position to be filled to the brim (it needs to be in a rainy zone with a large river system--rare, but it happens) it can sequester much of Tharn's liquid water. These water-hogs do eventually break up, but meanwhile, other seas shrink--and deserts spread.
• ELAFF: giraffe-like herbivores with dexterous trunks. One of the 13 intelligent species on Tharn. See Peoples for chart.
• FLUCTUS: flow, lava flow. The slopes of Tharn's SHIELD RANGES are massive overlapping basaltic flows. On Tharn they often form terraces with scalloped convex rims--fairly abrupt scarps, where an advancing wall of lave cooled and pooled. On Tharn they look more like built-up wax drippings than like Venus's pancakes or spiders or ticks (oh, my!), but it's the same principle.
• FLYOTE: winged canine omnivores, usually nesting in cliffs. One of the 13 intelligent species on Tharn. See Peoples for chart.
• FOSSA, FOSSAE: cracks. Usually, straight narrow canyons caused by crustal stretching or shrinking. Opportunistic rivers or lakes may follow or fill them later, but the water's not the cause. You can often spot fossae near TRENCHES--as the lower BED plate bends to slip under the UPLAND plate, this bending causes cracks parallel to the trench.
• FRACTURE ZONES: zones where RIFTS bend or split. Here, the BEDS (plains analogous to Terran seabeds) spreading from the rift jostle each other, cracking and slipping. They look like dirty glacier-faces, or "washboard" roads--parallel basins and ranges, cut at right angles by occasional ridges and deep crevasses. Fracture zones are higher than bed-plains, and capture a bit more rain, so they often have at least some woods, and streams or narrow lakes often lie in the canyons.
• FRONT RANGE: high mountain ranges at the edge of an UPLAND, Tharn's equivalent of a continent. Front ranges usually rise on PLATE boundaries, often a few hundred km "inland" of a TRENCH, where the rock from the lower plate melts and resurfaces in volcanoes. Also called RIMRANGE.
• HADLEY CELL: a loop of air, rising in a warm region, then traveling north or south as a high-altitude wind until it cools and grows denser, dropping back to the surface as a cool dry wind that heads back to where it rose, warming and picking up moisture as it goes--if it crosses water, that is. The rising zone is usually rainy; the falling zone, arid. Tharn, like Earth, has three Hadley cells, tropical, temperate and polar. The result: rainy belts around the equator and at 50-60 north and south, and a dry belt around 30.
• HOT SPOTS: a fairly stable plume of rising, hot magma in the mantle, causing vulcanism above. If the plate above is at rest, you get an Olympus Mons. If the plate's in motion, you get a SHIELD RANGE, a chain of Hawaiian volcanoes, the tallest and youngest right above the plume and older, eroded ones behind, where the hot spot once was. Tharn has three major hot spots generating shield ranges bigger than Hawaii.
• LANCHIKI: literally "de-awkwarding." A rigorous educational workshop, something between a marathon psychodrama / encounter group and a social-skills boot camp, offered to immigrants in the Heloon Basin. The curriculum includes:
  • Basic Bluntness
  • Sensory Differences Between the Thirteen Species of People
  • Principles of Co-op Life
  • When to Shut Up
  • Guidelines for Safe Interspecies Sex
  • Kindness Over Customs
  • What to Do with Rage at Your Own (many Heloonian immigrants were ostracized in their home villages).
• LEBBIRD: arboreal, winged felines who live only in deep trenches where the air is dense enough to fly in. One of the 13 intelligent species on Tharn. See Peoples for chart.
• LOBBRA: A big, hairy, zebra-striped, wisecracking lobster found on savanna plains. One of the 13 intelligent species on Tharn. See Peoples for chart.
• MAMOOK: A bipedal dinosaur with tusks, browsing the tundra with its handlike trunk. One of the 13 intelligent species on Tharn. See Peoples for chart.
• MOP: A shaggy-feathered marsupial biped, comfortable in cool forests. One of the 13 intelligent species on Tharn. See Peoples for chart.
• NECK = an isthmus or strip of land, usually fertile, between two of the many isolated seas on Tharn. One of the commonest terms used to divide the continentless surface. See also SHORE, BASIN.
• PLAIN: more specific than you think. On Tharn, a plain is a flat BED--a mid-altitude basaltic plateau analogous to Earth's abyssal plains--basically seabed without the sea. High-altitude plains are called PLANOS. The trenches are too small to have have extensive low-altitude plains.
• ORBITAL WINTER, ORBITAL SUMMER = seasons created as Tharn swings closer and further to the sun, not by axial tilt as on Earth. Axial seasons are hemispheric, but orbital seasons are worldwide--so even the Tharnian tropics have a definite annual cycle.
• PARRU: A domestic animal herded by thotters (see). Herbivorous, semi-aquatic, small duckbilled dinosaurs that breathe through a sort of living snorkel--the headcrest. The crest is also a resonator--the booming honks of a parru flock carries for miles, sounding like a band of drunk tuba players. The copious, rubbery eggs of the parru are a staple of thotter diet, and are an export item rivaled only by smoked fish and lotus seeds.
• PLAINLAKE, PLAINSEA = BEDLAKE, BEDSEA
• PLANO: a plateau of lighter "continental" rock, located in the uplands, often inland behind front ranges--what on Earth would be a continental interior. These high-altitude steppes and deserts resemble the Andean altiplano ecologically, hence the name. The standard planetological term PLANUM is broader--any plateau.
• PRAIRIE = a temperate grassland, getting at least occasional winter snow. Related terms: cool, windy STEPPES, frigid TUNDRAS, warm SAVANNA (snowless grassland with scattered trees or groves), and hot, dry VELDT (always treeless).
• RAINSHADOW: a mountain range or desert can strip winds of most of their moisture, so no rain falls downwind--it's cast a rainshadow! Single mountains can cast small rainshadows on their own downwind slopes, but rainshadows can be continental in scale. On the other hand, seas and rainforests moisten winds passing over them, erasing rainshadows. Even mountains or ridges casting rainshadows often trap enough rain to nourish high-altitude forests on their slopes and send streams down into the dry country at their feet, creating vital oases in the desert they also caused. Altitude giveth, and altitude taketh away...
• RAYS: Ridges of debris radiating out from an impact crater. Often porous and quickly eroded in wet climates, but they may persist millions of years in deserts. Some craters leave a broad cone of debris instead: a DEBRIS APRON.
• RIFT: a winding groove walled by twin ridges, often quite high and steep, where crust is spreading. On Earth, most are deepsea; but the rift valleys of East Africa are quite Tharnian. Rifts often hold long narrow lakes, like Tanganyika. Volcanoes tend to flank rifts, especially where they bend or fork. The standard planetological term is CHASMA, which implies no judgments about the cause of the feature, but I want to emphasize the parallels with Terran geology. Venus's chasmas are ambiguous in nature, but Tharn's chasmas are definitely spreading zones, rifts, like Earth's.
• RIMRANGE = on Earth these would be called coastal ranges. Wherever one plate slips under another, a SUBDUCTION TRENCH occurs. Usually the rim of the upper plate heightens into a rimrange. It's not just tilted up; as the lower plate's swallowed, sediment on it melts and rises, creating steep volcanic cones. The Cascades and Andes are classic examples. Also called FRONT RANGES
• RINGWALL = the circular rim of an impact crater. In Tharn's low gravity, these can be steep.
• SAVANNA = a patchwork of woods and grassland, or open woods with dry grass between trees. The dictionary definition of savanna is just "tropical grassland", but popular usage suggests scattered trees, and I use it as such for lack of a better word. For truly treeless tropical grasslands I use the unambiguous VELDT.
• SCARP = a sudden, steep slope or break. A broader term than cliff, which implies a near-vertical drop. Still, some scarps are true cliffs. In geology scarps often imply squeezing; on Tharn, the most common scarps are the edges of terraces--lava flows on the shoulders of shield volcanoes.
• SEA = any lake over 100,000 square km (40,000 sq mi--no freshwater lake on Earth would qualify, and neither would the Aral Sea.) Tharn has about 30 such seas, mostly shallow, their combined area is about 10 M sq km (4M sq mi--smaller than the Arctic Sea). The largest is about one million sq km.
• SHIELD, SHIELD RANGE: out on the BEDS, deep HOT SPOTS generate chains of broad, massive volcanoes, like the Hawaiian Chain. On Tharn, some climb out of the atmosphere entirely, like Mt Olympus on Mars. Shield volcanoes often have wide calderas (craters) and broad bases with gentle slopes, though their lava flows can create overlapping terraces ending in SCARPS. Opposite: STRATOVOLCANO.
• SHORE = a strip, usually fertile, bounded by a desert or mountain range inland, along one of the isolated oceans or seas. Used when BASIN or NECK are inapplicable. Tharn's continuous land divides into basins, shores and necks as naturally as Earth divides into continents and islands.
• SPLASH APRON, SPLASH RIDGES: When a meteor blasts out a crater, not all the material ends up in the ringwall. Both molten and solid debris falls outside the crater rim, usually thickest near the wall and tapering off--an "apron." Splash ridges are radial lines of fused debris, also called RAYS.
• STEPPE = a cool grassland with snowy winters, but thawing fully in summer. See VELDT, PRAIRIE, TUNDRA
• STRATOVOLCANO = a conical volcano built up of cinders or denser lava flows, much steeper than a SHIELD VOLCANO, with a smaller caldera (vent crater). Fuji is a classic stratovolcano.
• STRIKE-SLIP FAULT: a boundary between two PLATES where they slide laterally, with little subduction, causing earthquakes, creeping ground, and disrupted drainages (rivers bent like Zs).
• SUBDUCTION: when one tectonic plate gets pressed hard enough against a neighbor to be forced under it. A TRENCH forms, and FRONT RANGES rise along this line of doubled crust-thickness. Once the lower plate's rocks have slid laterally 1-300 km past the trench, they get deep and hot enough to melt and rise as magma, so volcanoes stud many front ranges.
• TECTONIC: literally, it just means ground movements--geology in general! PLATE tectonics, common to Earth and Tharn (but not Mars, for example) implies a quite specific pattern of crustal plates riding on deeper convection currents--the plates collide, creating ARC RANGES and TRENCHES at their boundaries.
• THOLUS: a steep volcano, like Fuji--usually conical, occasionally a dome. Common near edges of plates, around TRENCHES and ARC BASINS, like Earth's "Ring of Fire" around the Pacific. Contrasts with SHIELD, a broad, massive Hawaiian-type volcano.
• TRADE CAMAROO: Tharn's trade language, a streamlined version of the dialect spoken by camaroos around Trunzip Pass, where most trade between hemispheres crosses. Most caravan-crews around Tharn are camaroo-dominated, as are many long-distance traders. Trade Camaroo has also become the native tongue in the "melting pot" of Heloon Crater, Tharn's largest city-state; the many species living there have greatly enriched it. This Heloon dialect is steadily taking over, becoming a second language for peoples all over Tharn.
• TRENCH: a narrow, deep valley at a plate boundary, where one plate slips under another. On Earth such trenches are all undersea; on Tharn, most are exposed. They drop as much as 9 km below the plains. TRENCHLAKES often fill the bottoms. The air in deep trenches is up to twice as dense, creating more Earthlike conditions: AIR OASES. In particular, flight is much easier.
• TRENCHLAKES: long narrow lakes in the depths of plate-boundary trenches, like our Dead Sea, but far larger and deeper. Their surfaces vary in altitude from just below DATUM to 7 km down--23,000' below the plains. Past 3 km down, the air grows noticeably denser, holding more moisture and blocking UV. Unique ecologies flourish in these almost Terran AIR OASES.
• TUNDRA = Tharnian tundra isn't really. Properly, tundra means grassland with permafrost (perpetually frozen soil) beneath it--a relic of our last Ice Age. But Tharn's had no recent ice ages; even the land near the ice caps freezes only at the surface, and thaws entirely in summer--briefly. It looks much like Terran tundra and is just as cold and limited in species--grasses and lichens, mostly. Wide tundras, in this loose Tharnian sense, border both polar caps.
• UPLAND: the highest of Tharn's three terrain-levels (uplands, beds and trenches). Analogous to Earth's continents, they're lighter rock riding tectonic plates. Climate atop these plateaus is cold and dry, with very thin air. Many uplands do have greener, mountainous rims of FRONT RANGES, and some extend ARC RANGES out into the lowlands, cutting off leaf-shaped ARC BASINS (analogous to island arcs and coastal seas off Terran continents). Inland lie PLANOS--high cold grassy plateaus in the tropics, cold deserts further from the equator. One unearthly feature: where front ranges don't border uplands, they often drop off inconclusively--there's no equivalent of a continental shelf.
• VELDT = warm, dry, treeless grassland, as opposed to SAVANNA (warm, dry, but with some trees), PRAIRIE (temperate grassland with occasional snow), STEPPE (cool, with substantial winter snow), and TUNDRA (frozen most of the year).
• VELTAUR: a centauroid of the warmer grasslands. One of the 13 intelligent species on Tharn. See Peoples for chart.
• WINGBOK: A winged antelope found in TRENCHES; a dwarf phenotype roams the BEDS. One of the 13 intelligent species on Tharn. See Peoples for chart.
• WUKALU: literally "ticking" or "mosquito-ing"--that is, parasitism. It's the only Tharnian word for social exploitation. They'd see hundreds of Terran terms--war, racism, slavery, sexism, genocide, intimidation, colonialism, blackmail, servitude, atrocity, cannibalism, plutocracy... all as just fine shadings of wukalu, like the myriad Inuit words for snow. Now, the word wouldn't exist if Tharnians didn't do it--individually, occasionally. But social disapproval is high: for wukalu is the antonym, the exact reverse of yitlaki, the Tharnian cardinal virtue: sensitivity or empathetic alertness.
• YITLAKI: literally "awareness," but connoting emotional and social sensitivity as well as intelligence--"wise empathy" might be a better translation. The core Tharnian virtue--understandably so, for paying close attention to each others' feelings is vital to avoid conflict, with thirteen intelligent species on one little moon.
• ZEET: literally "sour harmony"--an arthom term that's spread into the trade lingo. It means a false consensus, in which some voices have been muted out of a need to fit in (a strong need for many Tharnian species who evolved in herds). All human politics would of course be seen as extremely zeet, but even Tharnian politics, based on broad consensus, stumbles due to zeet problems. The Tharnian solution is increased political yitlaki--actively asking dissenters to clarify what's gone wrong.

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