I am told this is a classic papper. Here are some notes / excerpts:
“Basaltic magma is derived by incongruent partial melting of mantle peridotite, favoured in tectonic settings (e.g. hotspots and rifts) where mantle rock rises adiabatically to relatively shallow levels, or in subduction-zone settings where volatiles decrease the melting temperature of mantle rock.”
Important magma parameters (pretty uniform for basaltic volcanos)
Magma density relative to lithosphere density — helps deter- mine the positions of magma chambers and intrusions;
Viscosity and yield strength determine the geometry and structures of lava flows and intrusions;
Gas content + viscosity + rheology controls the explosive violence of eruptions by determining the ease with which gases escape from magmas.
Parameters responsible for diversity: magma-supply rate and involvement of non- magmatic water.
”Basaltic systems have a source in the mantle from which magma ascends, mainly because of its positive buoyancy but sometimes aided by tectonic forces, toward the surface. They have one or more conduits by which the magma ascends. Polygenetic volcano systems generally possess a high-level magma chamber, situated at a neutral buoyancy level, which stores magma and modulates its delivery to the volcano and to sub-volcanic intrusions. Deep storage reservoirs may also exist.”
Types of volcanos
Shield volcanos
Stratovolcanos
Central Volanos.
Monogenetic volcanoes. These consist of clusters of scattered and mostly small (> 2 km3) volcanoes, each generated by a single eruption. Most commonly a volcano con- sists of a cinder cone associated with outflows of aa lava, but some are lava shields of scutulum- type (e.g. Rangitoto Island, Auckland, and Xitle in M…, and many that occur near the coast or close to lakes are phreatomagmatic tuff-rings or maars.
Flood basalt fields consist of monogenetic volcanoes erupted from widely scattered vents, but their lava flows cover wider areas, overlap or are superposed to form parallel-stratified successions, and have much greater volumes. Giant flood-basalt fields are distributed through geological time at average intervals of 32 Ma (Rampino & Stothers 1988), and each one formed at the time of inception of a hotspot, on arrival of an ascending mantle plume at the asthenosphere/litho- sphere boundary.
Volcano Collapse due to instable foundations, layers of pyroclastic or hydrothermally-altered material, intrusive dykes, local updomings in central volcanoes, severe marine erosion.
Polygenetic vs. monogenetic. “In the polygenetic volcano systems, magma batches ascend sufficiently frequently along the same conduit that the conduit walls are maintained in a hot condition and provide magma with a thermally and mechanically very favour- able pathway toward the surface. In the monogenetic and flood basalt systems magma batches ascend at such long time inter- vals that the pathway taken by one batch has effectivelycooled by the time that the next batch is ready to ascend.”
Fissures / Rift systems. ‘Most basaltic eruptions occur from fissures, and virtually all basaltic volcano systems have eruptive fissures. Fissures are opened very easily by the hydraulic jacking action of magma, and are the ‘natural’ underground conveyance for low- viscosity magma (Emerman & Marrett 1990). They commonly extend for tens of kilometres and are typically concentrated into rift zones. Magma solidified in fissures forms dykes. Dykes have a high survival potential, and in deeply eroded areas may be virtually all that survives of the volcanic system.
I picked up this book, probably about a year ago, at the recommendation of Dan Russell. Right now, I am about a quarter of the way through it, and it is a wonderful compilation of essays. She is a superb writer, and particularly her descriptions and imagery of the natural world is remarkable.
I like her aim as well:
What science does is what I would like more literature to do too: show us that we are living in an exquisitely complicated world that is not all about us. — Helen Macdonald, Vesper Flights. p. ix
Favorites
2. Nothing Like a Pig.
9. Ants
10. Symptomatic
12. Winter Woods
1. Nests
This essay describes nests. She begins with her feelings about nests develop when she was a child, and encountered them in her yard. She then goes into the present, and reflects more on this than their meanings.
*2. Nothing like a Pig
This essay describes an encounter with a boar. She reflects both on the boar, and more in general on animals in particular, and how the conception of an animal differs from the reality of the animal
Then it happens: a short, collapsing moment as sixty or seventy yards away something walks fast between the trees, and then the boar. The boar. The boar.
– Vesper Flights, Helen Macdonald, p 11.
A great bit of writing. The “short, collapsing moment.” The uncertainty about distance — :sixty or seventy yards” — and what she is seeing — “something.” The revelation: “and then the boar.” And the repetition: “The boar. The boar.”
3. Inspector Calls
A very nice short piece about an encounter with autistic boy, who is visiting her flat with his parents. In particular he connects with her bird and the bird with him.
4. Field Guides
“Field guides made possible the joy of encountering a thing I already knew but had never seen.”
5. Terkels Park
An essay on the place where she grew up. A bit nostalgic, but it was unusual, and had interesting reflections, so I found it worth reading. Some very nice writing:
I could lie awake in the small hours and hear a single motorbike speeding west or east: a long, yawning burr that dopplered into memory and replayed itself in dreams.
— ibid. p 12
My eyes catch on the place where the zoetrope flicker of pines behind the fence gives way to a patch of sky with the black peak of a redwood tree against it and the cradled mathematical branches of a monkey puzzle, and my head blooms with an apprehension of lost space,
— Ibid. p 13
6. High-Rise
About watching migrating birds at night from the top of the Empire State Building. An interesting discussion of how birds migrate — the height and speeds at which they fly, and the way they navigate — and the problems that the lights and tall buildings of the city give them.
7. The Human Flock
“Overhead a long wavering chevron of beating wings is inked across the darkening sky.“
Recounting the observation of large flocks of migrating cranes, and continuing to a discussion of the dynamics of swarms and murmurations. “Turns can propagate through a cloud of birds at speeds approaching 90 miles an hour…” This segues into a concluding comment on refugees, and a plea to regard them as individuals rather than masses.
8. The Student’s Tale
An account of meeting a student who is a refugee and spending time in camps…
A great opening sentence:
There’s a window and the rattle of a taxi and grapes on the table, black ones, sweet ones, and the taxi is also black and there’s a woman inside it, a charity worker who befriended you when you were in detention, and she’s leaning to pay the driver and through the dust and bloom of the glass I see you standing on the pavement next to the open taxi door and your back is turned towards me so all I can see are your shoulders hunched in a blue denim jacket.
— The Student’s Tale, Vesper Flight, Kate Macdonald, p. 53
I think this is a marvelous stream-of-consciousness sentence, with the writers attention shifting from taxi to grapes to taxi to the woman and then to the student whose shoulders are hunched. The second person is also very effective.
*9. Ants
About the mating flights of ants, and the birds that prey upon them. Also reflects on the power of scientific understanding to enhance the beauty of things, rather than detract: “…it’s things I’ve learned from scientific books and papers that are making what I’m watching almost unbearably moving.”
A red kite joins the flock, drifting and tilting through it on paper-cut wings stamped black against the sky.
[…]
The hitching curves of the gulls in a vault of sky crossed with thousands of different flightiness, warm airspace tense with predatory intent and the tiny hopes of each rising ant.
— Helen Macdonald, Vesper Flights, p. 63
*10. Symptomatic
Discusses her experiences with migraines. The writing is beautiful and ranges from describing the onset and symptoms of her migraine, to the way in which she has come to live with them. Ends with a partial analogy to earth undergoing climate change…
I was busily signing books when a spray of sparks, an array of livid and prickling phosphenes like shorting fairy lights, spread downwards from the upper right-hand corner of my vision until I could barely see through them. —Helen Macdonald, Vesper Flights, p. 66
11. Sex, Death, Mushrooms
On mushroom hunting: “It is raining hard, and the forest air is sweet and winey with decay.“
The air is damp and dark in here. Taut lines of spider silk are slung between their flaking trunks; I can feel them snapping across my chest. Fat garden spiders drop from my coat on to the thick carpet of pine needles below. —Helen Macdonald, Vesper Flights, p. 80
* 12. Winter Woods
Beginning with her custom of walking in the woods every New Year’s day, she reflects on the things that are distinctive about forests in winter. From the revelation of the landscape, to the bark textures and angled branches of leafless trees, to the sometimes transitory life that becomes evident. Winter woods, she suggests, are full of potential:
So often we think of mindfulness, of existing purely in the present moment, as a spiritual goal. But winter woods teach me something else: the importance of thinking about history. They are able to show you the last five hours, the last five days, the last five centuries, all at once. They’re wood and soil and rotting leaves, the crystal fur of hoarfrost and the melting of overnight snow, but they are also places of different interpolated timeframes. In them, potentiality crackles in the winter air. —ibid., p. 85
Eclipse
On viewing a solar eclipse. The phenomenology of the event, but also the deep, irrational, fundamental, emotional impact. The essay is reminiscent of Joan Didion’s essay, and in particular the way in which the fading daylight alters the colors in ways that cast the landscape in an alien light. It ends, beautifully, with a description of the light returning, and the emotions that brings.
In Her Orbit
A description of a trip with an astrobiologist to study extremophiles at very high altitudes in the Andes. Some beautiful descriptions of desolate and unworldly environments.
Hares
A description of the phenomenon of boxing hares, their place in English thought and mythology, and their decline due to environmental change.
Lost, But Catching Up
A very short essay description her intersection with a hound that was trying to catch up to the pack during a fox hunt.
Swan Upping Nestboxes
About the English tradition of “Swan Upping,” and her experience observing the activity; all interladen with reflections on the role of tradition and its uneasy releationship to Brexit, which had recently occurred.
F (Foidite)—When possible, classify/name according to the dominant feldspathoid. Melilitites also plot in this area and can be distinguished by additional chemical criteria.
(*)Sodic as used above means that Na2O – 2 is greater than K2O, and potassic that Na2O – 2 is less than K2O. Yet other names have been applied to rocks particularly rich in either sodium or potassium—as are ultrapotassic igneous rocks.
Lava flows from Mauna Loa
Palagonite
About Palagonite
Palagonite is an alteration product formed from basaltic glass (tachylite); concentric bands of it often surround kernels of unaltered tachylite, and are so soft that they are easily cut with a knife. In the palagonite the minerals are also decomposed and are represented only by pseudomorphs.
Palagonite soil is a light yellow-orange dust, comprising a mixture of particles ranging down to sub-micrometer sizes, usually found mixed with larger fragments of lava. The color is indicative of the presence of iron in the +3 oxidation state, embedded in an amorphous matrix.
Palagonite tuff is a tuff composed of sideromelane fragments and coarser pieces of basaltic rock, embedded in a palagonite matrix. A composite of sideromelane aggregate in palagonite matrix is called hyaloclastite.
Formation of Palagonite
Phreatomagmatic. Palagonite can be formed from the interaction between water and basalt melt. The water flashes to steam on contact with the hot lava and the small fragments of lava react with the steam to form the light-colored palagonite tuff cones common in areas of basaltic eruptions in contact with water.
Weathering. Palagonite can also be formed by a slower weathering of lava into palagonite, resulting in a thin, yellow-orange rind on the surface of the rock. The process of conversion of lava to palagonite is called palagonitization.
Tachylite
About Tachylite (tachylyte)
Tachylite (from ταχύς, meaning “swift”) is a form of basaltic volcanic glass formed by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is decomposable by acids and readily fusible. The color is a black or dark-brown, and it has a greasy-looking, resinous luster. It is often vesicular and sometime spherulitic. Small pheoncrysts of feldspar or olivine are sometimes visible. Fresh tachylite glass often contains lozenge-shaped crystals of plagioclase feldspar and small prisms of augite and olivine, but all these minerals occur mainly as microlites or as skeletal growths with sharply-pointed corners or ramifying processes.
All tachylites weather easily and become red to brown as their iron oxidizes.
Formation
Three modes of occurrence characterize this rock. In all cases they are found under conditions which imply rapid cooling, but they are much less common than acid obsidians. (Alkaline rocks have a stronger tendency to crystallize (i.e. not form glass), in part because they are more liquid and the molecules have more freedom to arrange themselves in crystalline order.)
Scoria
The fine scoria (aka cinders) thrown out by basaltic volcanoes are often spongy masses of tachylite with only a few larger crystals or phenocrysts imbedded in black glass. Basic pumices of this kind are exceedingly widespread on the bottom of the sea, either dispersed in the pelagic red clay and other deposits or forming layers coated with oxides of manganese precipitated on them from the sea water. These tachylite fragments, which are usually much decomposed by the oxidation and hydration of their ferrous compounds, have taken on a dark red color (scoria is from σκωρία, skōria, Greek for rust.); this altered basic glass is known as “palagonite.” [see above]
Lava flows
In the Hawaiian Islands volcanoes have poured out vast floods of black basalt, containing feldspar, augite, olivine, and iron ores in a black glassy base. They are highly liquid when discharged, and the rapid cooling that ensues on their emergence to the air prevents crystallization taking place completely. Many of them are spongy or vesicular, and their upper surfaces are often exceedingly rough and jagged, while at other times they assume rounded wave-like forms on solidification. Great caves are found where the crust has solidified and the liquid interior has subsequently flowed away, and stalactites and stalagmites of black tachylite adorn the roofs and floors. On section these growths show usually a central cavity enclosed by walls of dark brown glass in which skeletons and microliths of augite, olivine and feldspar lie embedded
Dikes and Sills
A third mode of occurrence of tachylite is as margins and thin offshoots of dikes or sills of basalt and diabase. They are often only a fraction of an inch in thickness, resembling a thin layer of pitch or tar on the edge of a crystalline diabase dike, but veins several inches thick are sometimes found. In these situations tachylite is rarely vesicular, but often shows pronounced fluxion banding* accentuated by the presence of rows of spherulites that are visible as dark brown rounded spots. The spherulites have a distinct radiate structure and sometimes exhibit zones of varying color. The non-spherulitic glassy portion is sometimes perlitic, and these rocks are always brittle. Common crystals are olivine, augite and feldspar, with swarms of minute dusty black grains of magnetite. At the extreme edges the glass is often perfectly free from crystalline products, but it merges rapidly into the ordinary crystalline diabase, which in a very short distance may contain no vitreous base whatever. The spherulites may form the greater part of the mass, they may be a quarter of an inch in diameter and are occasionally much larger than this.
Flow banding is caused by friction of the viscous magma that is in contact with a solid rock interface, usually the wall rock to an intrusive chamber or the earth’s surface.
The friction and viscosity of the magma causes phenocrysts and xenoliths within the magma or lava to slow down near the interface and become trapped in a viscous layer. This forms laminar flow, which manifests as a banded, streaky appearance.
Flow banding also results from the process of fractional crystallization that occurs by convection if the crystals that are caught in the flow-banded margins are removed from the melt. This can change the composition of the melt in large intrusions, leading to differentiation.
From GPT:
Fluxion banding results from shear forces within a moving magma body. This can happen in several ways:
1. Differential Flow in Lava. As lava moves, its viscosity varies due to cooling and crystallization. The outer layers, which cool faster, may develop a plastic or solid crust, while the inner material remains fluid. This difference in viscosity causes layers of magma to stretch and deform, forming elongated bands.
2. Crystal Sorting and Alignment. “ As magma flows, mineral crystals within it may become aligned due to shear stress. This is common in silicic lavas like rhyolite and dacite, where feldspar and quartz can form parallel bands.
3. Magma Mixing and Compositional Banding. If two magmas of different compositions mix, they may not completely homogenize, leading to streaks of contrasting compositions that appear as bands.
4. Intrusive Settings. In some plutonic rocks, fluxion banding may form as a result of late-stage magmatic flow, where crystals and melts segregate due to convection or deformation.
Kilauea: Dynamics of eruptions; Magma types
over the last 4 decades Kilauea has been very active, erupting both from Haumaumau crater on its summit and various rifts on its east side.
in 1983 Kilauea longest and most voluminous outpouring of lava from Kīlauea’s East Rift Zone in over 500 years. It resulted in the creation of the Pu‘u ‘Ō‘ō cone and extensive lava flows that covered significant areas, destroyed numerous structures, and added new land to the island.
Kilauea erupted on 4 May 2018 — it was an east rift zone eruption following the collapse of the Pu’u O’o vent. The rift eruption was driven by collapse of the central (shallow) magma chambers
The 2018 rift eruption had at least three different magmas:
a highly evolved cool (1110°) viscous lava presumably from sources in the rift system [May 3-9]
a less evolved hot (1130°) more fluid lava [May 17-18…]
a very hot (1145°) magma lacking the cargo of low temperature crystals of the previous lavas, but with olvine with high levels of MgO indicating magma > 1250° somewhere in the feeder system
“The first two were the chemically evolved basalt of the initial fissures and the highly viscous andesite. Both are volumetrically minor sources that represent distinct pockets of old residual magma from Kīlauea’s east rift zone that evolved for more than 55 years, cooling and crystallizing at depth. The third and volumetrically more substantial source was less-evolved and hotter basalt of fissure 8. This source was similar in composition to the magma erupted at Kīlauea in the years before 2018 and was ultimately derived from the summit region. Draining and collapse of the summit by this voluminous eruption may have stirred up deeper, hotter parts of the summit magma system and sent mixed magma down the rift..”
Things I’ve learned re eruption dynamics and magmas
Not all lava from Hawaiian volcanoes is basaltic
Even that that is basaltic, changes in composition; each eruption features at least one, and often several, unique lava compositions.
Magma chambers are not homogeneous; this is presumably even more true of rift systems, where greater cooling can generate mushes of crystals
The 2018 Kilauea rift eruptions were driven by collapse of summit magma chambers.
The 2018 Kilauea rift eruption exhibited periodicity of 2-3 days (surges that began within minutes of caldera collapses 40 K upslope) and 5-10 minutes (pulses driven by local outgassing changes )
The dynamics of an eruption can be mapped into several stages
Lateral injection of magma into a rift zone (which forms, in Hawaii, due to volcano flanks sliding into ocean) leads to initial eruption
Pressure in the rift system leads to its elaboration – advancing dikes may capture pockets of highly evolved magma with mushes of low temperature crystals.
Magma injection into rifts, if large enough, can trigger slip on caldera ring faults
Ring fault slippage can add pressure to rift system and drive eruptive behavior at the rift
The central magma chamber appears to be vertically zoned. Initial eruptions of the rift zone (after flushing out pockets of magma that have evolved in the rifts) are composed of younger magmas from lower in the chamber; summit eruptions are fed by older, more evolved magma, higher up in the chamber.
The 2018 Kilauea eruption produced lava at volumes of 100 meters3/sec
Stages of Hawaiian volcanoes: pre-shield (alkalic basalt & basanite); shield (thoelitic basalt derived from both shallow plumbing system and deep plumbing system adjacent to mantle); post-shield (alkalic basalt from deep plumbing system adjacent to mantle (shallow plumbing has crystalized)); post erosional/rejuvenated (alkalic basalt, basanite & nephelinite from ???)
Order and nature of basaltic mineral & crystals
Common minerals that crystallize from basaltic magma, ordered by the temperatures at which they typically form:
*Olivine (Ca2(Mg,Fe)4O4): This is one of the first minerals to crystallize at the highest temperatures, typically around 1,200°C to 1,300°C. Olivine is rich in magnesium and iron and is often found in the earliest stages of crystallization in basaltic magmas. *Olivine crystals are olive-green to yellow-green color. It often has a glassy or vitreous luster, and the crystals can be angular or rounded, with a granular texture when present in volcanic rocks. When olivine crystals are large enough, they often appear as transparent or translucent, sometimes with visible crystal faces, which are usually in a near-rectangular shape. When olivine is exposed to oxidation, especially under conditions of high temperatures or in the presence of oxygen, it can alter to a yellowish or brownish hue, sometimes developing a reddish or rusty tint due to the formation of iron oxide minerals.
*Pyroxene (e.g., augite, diopside): Pyroxenes crystallize at slightly lower temperatures, generally around 1,100°C to 1,200°C. These minerals are composed of chains of tetrahedra and are rich in iron and magnesium. *Augite crystals are dark green to black, often with a shiny, almost metallic luster. It crystallizes in short prismatic crystals, which are often rectangular or blocky in shape. Augite crystals are typically larger than many other basaltic minerals and can be quite visible in coarse-grained basalts. Augite, being rich in iron, may undergo partial oxidation upon exposure to the atmosphere. The oxidation often causes a darkening of the color to a more brownish or reddish tint, though it rarely forms the rusty, reddish color seen in olivine. Augite may also exhibit a duller or more matte luster when oxidized. *Diopside is another pyroxene mineral, typically appearing as light green to pale green, although it can also be colorless or pale yellow. It forms prismatic crystals that are often transparent or translucent. Diopside crystals have a glassy or vitreous luster and typically display distinct striations or fine parallel lines on their crystal faces.
*Plagioclase feldspar (labradorite, anorthite): Plagioclase forms between 1,000°C and 1,100°C in basaltic magmas. This mineral can range from calcium-rich (anorthite) to sodium-rich (albite) compositions, with the more calcium-rich varieties crystallizing at higher temperatures. * Plagioclase crystals vary from white to gray, and often have a glassy luster. They are typically tabular or blocky in shape and can show distinctive twin planes (known as albite twinning).
Magnetite (Fe3O4): Magnetite crystallizes at around 1,000°C to 1,100°C and often forms alongside other iron-rich minerals. It is a common accessory mineral in basaltic magmas. * Crystals not typically visible in lavas
Ilmenite (FeTiO3): Ilmenite forms at slightly lower temperatures, typically around 900°C to 1,000°C. It is a titanium-iron oxide mineral and often occurs in basaltic lavas. * Crystals not typically visible in lavas
Spinel (MgAl2O4): Spinel crystallizes at lower temperatures, usually around 900°C. It is a common accessory mineral in basaltic rocks, often forming in the lower temperature range of basaltic crystallization. * Crystals not typically visible in lavas
These minerals crystallize according to Bowen’s reaction series, where early-formed minerals (like olivine and pyroxene) are typically more magnesium- and iron-rich, while later-formed minerals (like plagioclase and spinel) are more silica-rich due to depletion of Mg and Fe.
