Cliff Walls Research Articles

Cosmogenic nuclide-derived downcutting rates of canyons within large limestone plateaus of southern Massif Central (France) reveal a different regional speleogenesis of karst networks

Abstract. We present 35 new burial ages (27 sites) based on 26Al / 10Be ratios of terrestrial cosmogenic radionuclides measured in clasts and sediments deep within 12 caves in the southern Massif Central, France. Our results, together with previously published burial ages, verify that cave morphogenesis has been continuously active in this region for at least the past ∼ 6 Myr. Combining sample burial ages with their associated cave elevation above the modern stream bed gives a mean regional incision rate of 88 ± 5 m Ma−1 for the Grands Causses area. South of the Cevennes Fault Zone bordering the Grands Causses, the incision rate is 43 ± 5 m Ma−1, suggesting that this difference might be accommodated by the fault zone. Sediment burial ages from caves which are not located on river valley flanks or cliff walls are surprisingly too young compared to their expected ages when calculated using this regional average river incision rate. This suggests that the classical epigenic speleogenesis model that presumes a direct correlation between cave level development and regional base level lowering does not apply for the study area. Therefore, we propose that regional speleogenesis is mainly controlled by the removal of ghost rocks by headward erosion from river canyons to central parts of the plateaus, emptying incipient primokarst passages to create cave systems. Our results suggest a continuum process from hypogene primokarst composed of passages filled with ghost rock to one of epigene karst dynamics emptying these passages and creating cave networks. We propose that these processes are the major mechanism in the southern Massif Central that initiates speleogenesis and controls the geometry of the networks. In this region, tiered karst cannot be associated with the pace of incision of the major rivers but must be explained by former ghost rock (or hypogene) processes.

The need to calibrate the surface hydrological model of Tenerife in the face of adverse meteorological phenomena such as the one that occurred on February 1, 2010, which produced heavy runoffs in Bco. de Santos.

The watershed of the Barranco de Santos is one of the largest on the island of Tenerife. The riverbed has its source at an altitude of 945 metres above sea level, on the Las Mercedes mountain, and flows through the Vega de La Laguna, descending towards the sea, bordering the Anaga mountains to the southwest and finally flowing into the Los Llanos dock in the port of Santa Cruz de Tenerife. Its route of more than 16 km has stretches where it becomes a real canyon, with cliff walls on its banks up to a hundred metres high. The average rainfall on the island of Tenerife is generally not very high, which means that the riverbed does not normally flow except in torrential episodes, which can cause unforeseen flooding, causing great material damage and even personal injury.\nDespite the large size of this basin, there are no flow gauges with which to estimate discharge volumes. This is mainly due to the fact that the episodes that produce runoff in the channel are usually sporadic and torrential. This document analyses the adverse phenomenon that occurred on 1 February 2010 and which gave rise to heavy runoff in the Barranco de Santos basin.

Die signifikanten Merkmale der entdeckten Amduat-Fragmente im Grab KV 38

Summary In 2019 and as part of the project “Thutmose’ I Amduat-Specimen”, further research work was performed at the tomb KV 38. During last course of this exploration, I achieved to secure more small mud-plaster fragments of the Book of Amduat, of which the cliff walls of the burial chamber were decorated. These different Amduat fragments can be identified as a part of the fourth, eighth, and ninth hour of the Book of Amduat. About the ninth hour there had never been a hint or a corresponding mention of it before. Therefore, this is also a piece of new archaeological evidence. After a comparative analysis of the paleographic and iconographic features of the displayed scenes on the newly found Amduat fragments with similar scenes from the tomb KV 34, it could be proved that there is a definite development between the time of Thutmose I and his successors. Furthermore, these sections highlight the iconographic features of the Amduat version of Thutmose I – their characteristic attributes and archaic decoration style form the original basis on which all subsequent versions have been built. Thus, this version could be the earliest source of the theological underworld books of the early 18th Dynasty.

Jarosite-Rich Mineral Crust on Coastal Cliffs in Central Norway: Microstructural and Geochemical Investigations

The study of jarosite produced under diverse conditions is essential to gain insight into its diverse formation mechanisms on earth. Such investigations can even pave ways to better understanding of the genesis of jarosite discovered in extra-terrestrial bodies such as Mars. Jarosite samples from two costal locations in central Norway are investigated through the application of multiple analytical techniques. The jarosite-rich encrustations on seaward cliff walls were studied with a focus on the characterization of their micromorphology and geochemistry. Light and electron microscopic analyses revealed distinct laminations and microlaminations in the samples. These layered laminations likely imply the existence of favorable periods in a cyclic manner for mineralization/biomineralization of jarosite in tandem with gypsum formation and dissolution. The pH level measured is not low similar to that usually described as conducive for jarosite formations. Different viable jarosite formation mechanisms are explored. Though some indicators are implied from microstructural and compositional analyses, further investigations are required for establishing the biogenic nature of the mechanism involved. Signs of the possible formation of jarosite in the Mid-Pleistocene Transition, 1.1–1.3 million years B.P., are acquired from Ar39/Ar40 geochronological determinations. Useful paleoenvironmental and paleobiological information could be found preserved in the microstructures of such jarosite formations.

Surveying cliff-nesting seabirds with unoccupied aircraft systems in the Gulf of Alaska

Drones, or unoccupied aircraft systems (UAS), can transform the way scientific information on wildlife populations is collected. UAS surveys produce accurate estimates of ground-nesting seabirds and a variety of waterbirds, but few studies have examined the trade-offs of this methodology for counting cliff-nesting seabirds. In this study, we examined how different UAS survey parameters might influence seabird counts for population monitoring and assessed behavioral responses to aerial surveys for three sub-Arctic seabird taxa in the Gulf of Alaska: common murres (Uria aalge), black-legged kittiwakes (Rissa tridactyla), and pelagic and double-crested cormorants (Phalacrocorax pelagicus and Phalacrocorax auritus). We flew two commercially available models of UAS in planned approaches at different speeds and distances from colonies during incubation and chick-rearing periods. We compared counts from UAS-derived images with those from vessel-based photography and assessed video recordings of individual birds’ behaviors for evidence of disturbance during UAS operations and control phases. Count estimates from UAS images were similar to or higher than those from conventional vessel-based images, and UAS were particularly effective at photographing birds at sites with high cliff walls or complex topography. We observed no significant behavioral responses to the UAS by murres or cormorants, but we did observe flushing by black-legged kittiwakes during UAS flights; most of these birds were not incubating or brooding. At both the colony and individual level, we observed slightly greater responses to the smaller UAS platform and closer approaches. These results inform both species specific and general best practices for research and recreational usage of UAS near cliff-nesting seabird colonies.

Rehabilitasi Tebing Sungai Guo Akibat Banjir Bandang di Area Bypass Kota Padang

After an earthquake hit the West Sumatra Province in 2009, Padang, as the provincial capital, moved the centre of its government activities to Bypass. Following the government's relocation, the community also moved to the Bypass area. Gradually this caused the area, which was initially a rain catchment area, to turn into a residential and office area. The loss of rain catchment areas increases the amount of runoff drastically. On August 18, 2021, the flood incident was also the cause of flash floods that hit many areas in Padang City, one of which was the Guo River area. The impact of this flood destroyed the cliffs of the Guo River. The cliffs were damaged due to sediment carried from upstream of the Guo River in the form of large rocks and the swift flow of water hitting the cliff walls of the Guo River. Not only destroying the cliff walls but also the access roads around the upper reaches of the Guo River. Therefore, Andalas University and the Guo River community members carried out rehabilitation activities for the Guo River. It was started by survey activity of the level of damage from the collapsed cliff. This was followed by sustainable planning related to the rehabilitation of the cliffs of the Guo River area and planned activities to be carried out to increase and develop the potential of Sugai Guo as a natural tourist attraction.

Rockfall susceptibility and runout in the Valley of the Kings

The UNESCO world heritage site Valley of the Kings or Wadi el-Moluk (وادي الملوك) near Luxor, Egypt, hosts unique burial places of Egyptian kings and royals from the New Kingdom (c. 1539–1075 BCE) and attracts about 0.5 to 2 million tourists per year. Very steep to subvertical cliffs of Thebes Limestone surround the Valley of the Kings. The rock mass is cut by frequent joints and faults making the cliff walls prone to rockfalls. However, only few rockfall debris are found in the valley, likely due to natural remobilisation by flood events and artificial clearings and excavation works that rendered the natural debris cover over the millennia. This work focuses on rockfall susceptibility and runout and makes use of new high-resolution landscape surface models utilising terrestrial laser scanning. We investigated rockfall release areas by exploring rock mass fractures at 23 cliff segments and analysed the kinematics of potential rockfalls. Furthermore, we estimated potential rockfall deposition areas with CONEFALL supported by nine numerical simulations of single rockfall events using Rockyfor3D. We found that nearly 4500 m2 (26%) of the public walking paths and 24 out of 64 tomb entrance areas locate within potential rockfall runout zones.

Natural Radiation Shielding on Mars Measured With the MSL/RAD Instrument

AbstractProtecting astronauts from the effects of space radiation remains one major stepping stone for the exploration of Mars. Long‐term exposure to radiation can lead to severe health effects and affects allowable mission duration. Mission designs for Mars include the use of radiation shelters that provide additional mass to surround the astronauts. This leads to incoming radiation losing energy through ionization processes. This is important during solar energetic particle events when solar protons can reach the surface with high intensities. Additionally, shelters provide a long‐term reduction of the exposure to galactic cosmic rays. As mass is an important time and cost factor in space travel, using natural sheltering already on Mars is a desirable option. One candidate is to use subterranean lava tubes that provide shelter from the radiation from above. Other options include craters, cliff walls, or rock overhangs. Here, we present the first in situ measurements of radiation sheltering by natural environments on the surface of Mars. The data were acquired with the Radiation Assessment Detector (RAD) on board the Curiosity rover in Gale crater on Mars. We show measurements from when Curiosity was parked close to Butte M12 in the Murray Buttes formation, which blocked out 19% of the surrounding sky view. During this time, from Mars Science Laboratory (MSL) sol 1456–1467, we find a decrease of 4% in the expected dose rate, and a decrease of 7.5% in the neutral particle environment. This proof of principle is an important step to validate plans to use natural sheltering on Mars.

Hurricane Gloria

Hurricane Gloria LAWRENCE DUGAN A screaming northern gale flew past his wild words And slammed the sails, and pulled a wave toward heaven. —Aeneid, i.102–3 (Sarah Ruden, trans.) i. A phalanx of weather tools at the door, A shovel, an ice-pick, an umbrella, A new cane, leaning against each other, Plastic fabricated to resist storms, Reminds me of a storm I rode out years ago, The Nor’easter of 1985, On the twenty-first floor of 5 Penn Center Across the street from where the Fox Theater Spread the bright wings of its marquee, folded Now forever, torn down, and then replaced With a glass-box not unlike the office I looked out of, watching the rain lashing Windows, tearing at the flags hung on poles On other buildings, solitary banners Left up as if to challenge the weather To do its worst, to refute the young storm Tearing northeast out of the Atlantic, Predicted only a few days before As a hurricane, that didn’t happen, But leaving the high-rise building nearly Deserted, with the ticker still running Across the wall; the market had opened Empty office or not, unoccupied Desks giving it that strange quietude Peculiar to such spaces, which the mind Expects to be filled, even while seeing Otherwise. arion 28.2 fall 2020 66 hurricane gloria I felt like a sailor for The only time in my life, stepping off The elevator at 21, and then Walking into the main hall and sensing The building swayed slighty, barely feeling It but knowing it distinctly, hearing It creak exactly as I had heard ships At sea in dozens of movies, and with The sound, the sway, the massive grid of pipes And beams giving and taking. jms Old timers hadn’t warned me about this Although some had ridden out several Storms as bad, real or metaphorical, Not even old Harris who remembered Moving down from Susquehanna county In ’29, to Wall Street and the Crash. ii. Future archaeologists of urban Storms will study pictures of umbrellas Taking flight, wrecked synthetic shapes blooming Against resistant hands, then abandoned, Stuffed into trash cans, twirling down alleys, Pastels, stripes or old-fashioned banker-black, The edge of the story, the windy street’s Last rebuke to those daring to stagger To lunch but caught in the nor’easterly Gale’s grey wall of wind and rain that rattled Doors and buckled windows. The building held Two dozen companies, and I still like To think one fronted for an anchorite, Some isolated individual Up on 24, alone at his desk In a skyscraper office for ten years Praying, sometimes looking down the cliff walls At the peregrine falcons sweeping home Lawrence Dugan 67 To their massive nest stuffed tight in the bronze Lap of a statue seated on City Hall, One of the allegories of Founders And Lenape chiefs placed high over Broad, The hawks diving downward athwart the storm Coming on in grey curtains wavering Over the city and the Delaware Valley. Across the river in Jersey The pines begin, in Camden the street dirt Is sand; halfway to the shore the forest Runs above the expressway, farms below, The pines flourishing in sandy barren Earth lacking nitrogen, incinerating Every dozen years, thousands of acres Blowing away in flames seen at the shore. After that rain those woods were safe for weeks. iii. Ten years and two jobs later I needed Census material and found it online On a rainy day in Center City In a high-rise office nearby, a halfDay ’s work done to my surprise in only Twenty minutes, then realizing as I Stood up from a computer that the view Was familiar. I was back on 21 In my old office; jms had moved But the grey sky cleared with a sweep of wind And the view north and south looked as before Wherever the market’s ticker-tape rolled now. The weather had surprised me again; The only full rainbow I ever saw, The ancient sign that spares the world from floods, A pure unblemished iridescent span, Appeared late in spring, in a sun shower. ...

Leaving the Gay Place: Billy Lee Brammer and the Great Society

Leaving the Gay Place: Billy Lee Brammer and the Great Society

KESEDIAAN MEMBAYAR MITIGASI LONGSOR DI KARANGANYAR DENGAN PENDEKATAN CONTINGENT VALUATION METHOD (Willingness to pay landslide mitigation in Karanganyar with the contingent valuation method approach)

Landslides are still a threat in some areas in Karanganyar Regency which has mountainous topography. Landslides cause in loss of property, and lives. Community participation in landslide mitigation is very important because the community is dealing directly with landslides. One of the roles of the community in landslide mitigation can be measured by the willingness to pay (WTP). The aims of this study are 1) to determine factors that influence WTP for reducing the impact of landslides, 2) to determine the value of WTP for landslides mitigation. The method used in this study is contingent valuation methods by calculating the amount of WTP to reduce the risk of landslides and the factors that affect WTP. This study used primary and secondary data. Primary data were obtained using open interview techniques with 100 respondents in some villages in Karanganyar District, who are at risk of landslides, while secondary data was taken from the Statistics Agency (BPS) and Regional Agency for Disaster Countermeasure (BPBD) of Karanganyar Regency. The results showed that incomes and poverty affected the WTP for landslide mitigation significantly. The average willingness to pay for landslide mitigation in the form of construction of cliff walls, closure of cracks and reparation of waterways in Karanganyar Regency is Rp. 26.307,00 per month.

Amduat-Exemplare von Thutmosis I.: Weitere Fundstücke im Grab KV 38

Summary This article deals with the further exploration in tomb KV 38 in the Valley of Kings. In the course of this exploration in early 2018 I discovered more small mud-plaster fragments of the Amduat book. These different Amduat fragments can be identified as a part of the fourth, sixth, seventh, eighth and tenth hour of the book of Amduat. Therefore, these Amduat fragments prove that possibly the cliff walls of the tomb of king Thutmose I were originally encased and decorated with a complete corpus of the book of Amduat (long version). After an examination of the displayed scenes and their comparison with similar sections of the Amduat from tomb KV 34 it turned out that both specimens show clear differences and that both tombs have manifold artistic variations. Therefore, both specimen are originate from different reigns and were not made by the same king.

First ROV Exploration of the Perth Canyon: Canyon Setting, Faunal Observations, and Anthropogenic Impacts

This study represents the first ROV-based exploration of the Perth Canyon, a prominent submarine valley system in the southeast Indian Ocean offshore Fremantle (Perth), Western Australia. This multi-disciplinary study characterises the canyon topography, hydrography, anthropogenic impacts, and provides a general overview of the fauna and habitats encountered during the cruise. ROV surveys and sample collections, with a specific focus on deep-sea coral, were conducted at six sites extending from the head to the mouth of the canyon. Multi-beam maps of the canyon topography show near vertical cliff walls, scarps, and broad terraces. Biostratigraphic analyses of the canyon lithologies indicate Late Paleocene to Late Oligocene depositional ages within upper bathyal depths (200-700 m). The video footage has revealed a quiescent ‘fossil canyon’ system with sporadic, localised concentrations of mega- and macro-benthos (~680-1800 m), which include corals, sponges, molluscs, echinoderms, crustaceans, brachiopods, and worms, as well as plankton and nekton (fish species). Solitary (Desmophyllum dianthus, Caryophyllia sp., Vaughanella sp., and Polymyces sp.) and colonial (Solenosmilia variabilis) scleractinians were sporadically distributed along the walls and under overhangs within the canyon valleys and along its rim. Gorgonian, bamboo, and proteinaceous corals were present, with live Corallium often hosting a diverse community of organisms. Extensive coral graveyards, discovered at two disparate sites between ~690-720 m and 1560-1790 m, comprise colonial (S. variabilis) and solitary (D. dianthus) scleractinians that flourished during the last ice age (~18 ka to 33 ka BP). ROV sampling (674-1815 m) spanned intermediate (Antarctic Intermediate Water) and deep waters (Upper Circumpolar Deep Water) with temperatures from ~2.5-6°C. Seawater CTD profiles of these waters show consistent physical and chemical conditions at equivalent depths between dive sites. Their carbonate chemistry indicate supersaturation (Ωcalcite ~1.3-2.2) with respect to calcite, but mild saturation to undersaturation (Ωaragonite ~0.8-1.4) of aragonite; notably some scleractinians were found living below the aragonite saturation horizon (~1000 m). Seawater δ13C and nuclear bomb produced Δ14C compositions decrease in the upper canyon waters by up to ~0.8‰ (< 800 m) and 95‰ (< 500 m) respectively, relative to measurements taken nearby in 1978, reflecting the ingress of anthropogenic carbon into upper intermediate waters.

Passive Spine Gripper for Free-Climbing Robot in Extreme Terrain

In this letter, we present a passive spine gripper that can hold rough rocky surfaces of boulders on cliff walls, and we discuss its application to a four-limbed robot for free-climbing in extreme terrain. The limbed robot has four degrees of freedom in each limb, where three are to drive joints of the limb and one for releasing the gripper. The fine spine of the proposed gripper also enables it to passively and adaptively latch on to microscopic asperities of the rough surface, and it is thus an efficient mechanism. In this letter, we present the fundamental design and mechanism of the proposed gripper, after which we introduce its static gripping model. We verify the gripping model by the experimental gripping performance of the prototype gripper. We show a lightweight four-limbed robot that is equipped with the grippers mounted on each limb. To evaluate the climbing capabilities of the robot, we use it to perform climbing experiments on a rugged and steep slope. The results show that the prototype can safely climb over such challenging terrain that is similar to a gravity offload system.

Bouldery slope landforms on Mt. Biseul, Korea, and implications for paleoclimate and slope evolution

AbstractIdentification of bouldery landforms in mountains and correctly understanding their formative processes play an important role in reconstructing the geomorphic history of a region. We propose that blocks were liberated by frost cracking and wedging of cliff walls during the last glacial period. However, we further suggest and test four hypotheses comprising different scenarios for preconditioning by chemical weathering and subsequent block transport using terrain analysis, characterization of boulders, and10Be exposure dating. Frost shattering from the backing cliff produced the boulders since the beginning of the last glacial period (~80 ka), and gelifluction transported them downslope throughout the last glacial period. Their activity then entered a dormant phase at the beginning of the Holocene. Distribution patterns of exposure ages of tors and block streams are similar to those of previous studies, implying that bouldery landscapes in the southern Korean Peninsula were likely to be formed by similar processes under periglacial conditions. The timing of active periods in transport of block streams corresponds well with the cold periods identified in regional and global climate proxy records. Interestingly, the activity of block streams in the study area reached a maximum during Marine Oxygen Isotope Stage 3 to 2 when the growth rate of nearby speleothems was lowest.

Scopelophila ligulatarecorded for the first time in northern Europe

Scopelophila ligulata (Spruce) Spruce is reported for the first time from Europe north of the Alps. The moss was discovered in crevices in south facing cliff walls of felsic volcanic rock on the island Varaldsoy in Hordaland County, southwest Norway, in September 2015.

Morphology and dynamics of the jets of comet 67P/Churyumov-Gerasimenko: Early-phase development

The OSIRIS camera onboard the Rosetta spacecraft obtained close-up views of the dust coma of comet 67P. The jet structures can be used to trace their source regions and to examine the possible effect of gas-surface interaction. Methods. We analyzed the wide-angle images obtained in the special dust observation sequences between August and September 2014. The jet features detected in different images were compared to study their time variability. The locations of the potential source regions of some of the jets are identified by ray tracing. We used a ring-masking technique to calculate the brightness distribution of dust jets along the projected distance. Results. The jets detected between August and September 2014 mostly originated in the Hapi region. Morphological changes ap- peared over a timescale of several days in September. The brightness slope of the dust jets is much steeper than the background coma. This might be related to the sublimation or fragmentation of the emitted dust grains. Interaction of the expanding gas flow with the cliff walls on both sides of Hapi could lead to erosion and material down-fall to the nucleus surface.

Insolation, erosion, and morphology of comet 67P/Churyumov-Gerasimenko

The complex shape of comet 67P and its oblique rotation axis cause pronounced seasonal effects. Irradiation and hence activity vary strongly. Aims. We investigate the insolation of the cometary surface in order to predict the sublimation of water ice. The strongly varying erosion levels are correlated with the topography and morphology of the present cometary surface and its evolution. Methods. The insolation as a function of heliocentric distance and diurnal (spin dependent) variation is calculated using >105 facets of a detailed digital terrain model. Shading, but also illumination and thermal radiation by facets in the field of view of a specific facet are iteratively taken into account. We use a two-layer model of a thin porous dust cover above an icy surface to calculate the water sublimation, presuming steady state and a uniform surface. Our second model, which includes the history of warming and cooling due to thermal inertia, is restricted to a much simpler shape model but allows us to test various distributions of active areas. Results. Sublimation from a dirty ice surface yields maximum erosion. A thin dust cover of 50 μm yields similar rates at perihelion. Only about 6% of the surface needs to be active to match the observed water production rates at perihelion. A dust layer of 1 mm thickness suppresses the activity by a factor of 4 to 5. Erosion on the south side can reach more than 10 m per orbit at active spots. The energy input to the concave neck area (Hapi) during northern summer is enhanced by about 50% owing to self-illumination. Here surface temperatures reach maximum values along the foot of the Hathor wall. Integrated over the whole orbit this area receives the least energy input. Based on the detailed shape model, the simulations identify “hot spots” in depressions and larger pits in good correlation with observed dust activity. Three-quarters of the total sublimation is produced while the sub-solar latitude is south, resulting in a distinct dichotomy in activity and morphology. Conclusions. The northern areas display a much rougher morphology than what is seen on Imhotep, an area at the equator that will be fully illuminated when 67P is closer to the Sun. Self-illumination in concave regions enhance the energy input and hence erosion. This explains the early activity observed at Hapi. Cliffs are more prone to erosion than horizontal, often dust covered, areas, which leads to surface planation. Local activity can only persist if the forming cliff walls are eroding. Comet 67P has two lobes and also two distinct sides. Transport of material from the south to the north is probable. The morphology of the Imhotep plain should be typical for the terrains of the yet unseen southern hemisphere.

Reward for Bravery

Reward for Bravery Laura Schadler (bio) I was born on a hill two blocks back from the Pacific Ocean. I was born in a garage apartment that I never saw, and then my parents moved even farther from the shore. That was before my father went back to Vietnam, taken with a violent nostalgia for war and obsessed with creating a family who wasn’t us, and before my mom moved up in the world, at least a little, to the white stucco house with hot pink weeds clamoring all over, the one we live in now. She called those voracious hot pink things a garden, the cactus too. We were close enough to where the rich people lived, so the rich people were our friends, invited my mom to their parties, and I slept in their bedrooms under soft, white comforters. Growing up, the water was everywhere. My best friend, Vee, had a house right on the cliffs. It was the real deal, with shining, silver cars covered up in the garage, and paintings splattered in grays and olive greens hanging on walls, everything worth millions. Her house would also be the first place to go if the earth moved at all underneath it, just sliding right down those cliff walls and being taken by the sea. No one seemed too concerned with that, though they should have been. Vee and I knew how precarious every structure was, including our own little skeletons, the black hole of ourselves, the crumpling center of our chests where each breath went. It didn’t matter what else we knew about geography; when we stood on Vee’s deck we knew it was the edge of the whole entire world, and also the end. In those days no one’s parents were concerned about the strength of the tide. We were allowed to do whatever we wanted. Even when we were far younger, we chased the edge of the water, smooth rocks in our hands, imaginary contests unfolding, as our parents stood with their backs to us. We took our shoes off when the water came in and trapped us along the cliffs, but nothing bad ever happened. We saw the lagoons of green far out, farther than we could swim. We were never trapped long. Our backs pressed against the red [End Page 20] silt, and the tide fell back again. In that way we were freed, again and again. “There are two tides each day,” Vee recited patiently, her wind-snarled hair pressed to her salty mouth. We both knew equal amounts about the water. I knew about the pressing core of the deep that lured sailors downward. I knew about the broken lighthouses, the shipwrecks, the women with pulsing, turquoise legs. Some nights I wished I were one of the latter, concerned only with swimming and water, as I mostly was any-way, and the considerations of a sky only over ocean, never over land. Some nights without Vee, I walked all those blocks to the beach from my own small house and pressed my feet into the sand all the way down to the break. I don’t want to admit it, exactly, that I hoped I might transform there in the dark all alone, with no one looking. I pinched my legs and threw myself on the ground and kicked and was still, but nothing. My human girl legs continued to stretch out long in front of me. The rich parents had granite-topped kitchen counters and leaned over them with wet glasses in their hands, gin and ice inside. We understood what they talked about, sort of. We eavesdropped when we remembered to. Their afternoon cocktail hours were a vague and daily anthropology class for us. It was the first time I heard words like hysterectomy, a thing that sounded medieval, or fugitive. Vee said it had something to do with what was essential to making us women, something inside us we might not be allowed to keep. Women had an ambivalent power, it was clear, something painful and put-upon about their air when they spoke to their husbands and sons, not that my mother had...

The surface composition of Iapetus: Mapping results from Cassini VIMS

Cassini VIMS has obtained spatially resolved imaging spectroscopy data on numerous satellites of Saturn. A very close fly-by of Iapetus on September 10, 2007 provided the best data on the spectral signature and spatial extent of dark material on Iapetus. This Cassini Rev 49 Iapetus fly-by provided spatially resolved imaging spectroscopy data of the dark material and the leading/trailing side transition from the dark material to visually bright ice on the trailing side. Compositional mapping and radiative transfer modeling shows that the dark material is composed of metallic iron, nano-size iron oxide (hematite), CO2, H2O ice, and possible signatures of ammonia, bound water, H2 or OH-bearing minerals, trace organics, and as yet unidentified materials. CO2 indicates a pattern of increasing CO2 strength from the leading side apex to the transition zone to the icy trailing side. A Rayleigh scattering peak in the visible part of the spectrum indicates the dark material has a large component of fine, sub-0.5-μm diameter particles consistent with nanophase hematite and nanophase iron. Spectral signatures of ice also indicate that sub-0.5-μm diameter particles are present in the icy regions. Multiple lines of evidence point to an external origin for the dark material on Iapetus, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the leading side, exposing clean ice, and slopes facing the leading direction which show higher abundances of dark material. Multiple spectral features and overall spectral shape of the dark material on Iapetus match those seen on Phoebe, Hyperion, Dione, Epimetheus, Saturn’s rings Cassini Division, and the F-ring implying the material has a common composition throughout the Saturn system. The dark material appears to have significant components of nanophase metallic iron and nanophase hematite contributing to the observed UV absorption. The blue scattering peak with a strong UV–visible absorption is observed in spectra of all satellites that contain dark material, again pointing to a common origin of contamination by metallic iron that is partially oxidized.