Category Archives: Volcanism

The Pink and White Terraces, Magic Lanterns, and 19th Century Narratives

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Preamble

A collection of late 19th century lantern slides made by Arthur Whinfield, a native of Worcester, England, has recently been restored and digitized.  I was alerted to the Whinfield collection by an old friend Justin Hughes, an archaeologist working in Worcester, UK, who indicated that the collection contained several slides of the famed Pink and White Terraces near Rotorua, New Zealand. These iconic geothermal wonders were destroyed by the eruption of Tarawera, on June 10, 1886.

Lake Rotomahana, in the shadow of Tarawera volcano, looks peaceful enough. Its waters are ruffled only by wind and the wakes of small boats. No hint of impending doom. No hint of the destructive explosions 132 years ago, eruptions that completely changed the local landscape, destroyed a village and its inhabitants, and obliterated a geological icon – the Pink and White Terraces.

New Zealanders look upon the Pink and White Terraces with a kind of fondness, even though no one alive has seen them. Mineral-rich waters spurting from geothermal springs and erupted from geysers above the former Lake Rotomahana, deposited silica in a cascade of rimmed terraces and pools; ever shrouded in steam. As their name indicates, there were two sets of terraces. The larger White Terraces descended 25m, stair-like, into the lake.  Their pink counterparts were terraced through 22m. Mineral content was more pronounced in the pink variety, with precipitation of arsenic and antimony minerals, and gold.

The terraces disappeared on June 10, 1886. Eruption of Tarawera was focused along a 17 km rift that extended from the volcano summit, through the terraces, and into Lake Rotomahana. Whether the terraces were obliterated, buried, or partly submerged in modern Lake Rotomahana is still debated.

By all accounts the terraces were spectacular; witness the written testimonies of geologists (like Ferdinand von Hochstetter in 1859) and Victorian gentlefolk, renditions in oil and water-colour (like the Blomfield painting above), and photographs – grainy, black and white, tinted amber with age. This was the late 1800s, and photography was in its infancy, the act of recording an image a laborious process.

Enter Arthur Whinfield. Whinfield was a peripatetic photographer who in the 1880s captured the magic of cities and landscapes in the Americas, Asia, Africa, Europe, Australia, and New Zealand. Part of his legacy resides in a collection of lantern slides (more than 2100 of them) that were donated to the Worcester Diocesan Church House Trust by his wife in 1918. A century later, in partnership with the Worcestershire Archive and Archaeology Service, the slides have been restored, digitized, and made available for public display. Included in the collection are 11 glass slides of the Pink and White Terraces, and the aftermath of the Tarawera eruption.

Whinfield took many of the photographs he used in his slides, but also borrowed from other photographers, and this seems to have been the case for several Pink and White Terraces images.  Te Papa Tongarewa  (the New Zealand National Museum) has an extensive, publicly accessible collection of photographs, paintings and prints related to the Terraces. I was able to identify individual photographers in some of the slides from the Te Papa collection.

Click on each image below for a larger format, then use the back-click arrow to return to the article.

The classic image of the Pink Terrace with Maori guides (or is this a family scene?) and a canoe in the foreground is shown below. This iconic photograph was taken by Burton Brothers Studio in 1885, and later used by Muir and Moodie Studio in a popular postcard (early 1900s; one penny postage required). Whinfield’s slide (left) is a copy of this scene (acknowledging the photographer on the lower left corner).

Whinfield slide left; Muir & Moodie postcard right

 

Moodie and Muir also produced a postcard from the White Terraces image below (left); the colour would have been added by hand to the printed photo. The Whinfield slide (right) is an uncoloured version of this image (compare the shape of the steam clouds at the top).  The terrace flights are nicely portrayed in this slide.

Muir & Moodie postcard left; Whinfield slide right

 

One of the more panoramic views of the White Terraces shown by Whinfield (left) is similar to a photograph taken by Burton Brothers in January-May 1886 (in the Te Papa collection) but is viewed from a lower elevation and records a different steam profile; the original photographer may have taken more than one shot from this location (I have not been able to determine who the photographer was for Whinfield’s slide). Here the terraces clearly dip their toes in Lake Rotomahana.  The terraces were a popular tourist attraction, in part because bathing was possible in the lower pools.

Whinfield slide left; Burton Brothers photo right

 

The original black and white photograph for the three slides below (Pink Terraces), was taken by Charles Spencer.  The three Whinfield slides are identical, with the right image slightly enlarged and a mirror of the other two. The view provides some detail of several small pools that appear to have been filled completely by silica.

 

The two slides below show detail of White Terrace pools and the intricate patterns wrought by precipitation of silica.  Dark stains daubed on the pool walls may have been algae. I have not been able to determine the attribution of either slide. The slide on the right is labelled ‘White Terrace Crater’ and may have been taken close to one of the active geysers near the top of the terraces.

 

Whinfield’s slide (below, left) showing the aftermath of the eruption at McRae’s Hotel is slightly different to one taken by photographer George Valentine (1886, McRae’s Hotel and Sophia’s whare) – the man on the right in Valentine’s image has his arms folded; in Whinfield’s slide they are not. The viewing angle is also slightly different – the ladder (foreground) is more oblique in the Whinfield slide.  The hotel probably collapsed under the weight of volcanic ash. Other photographs (not in the Whinfield collection) show the back of the hotel to be demolished completely. The trees were also stripped of foliage.

Whinfield slide right; George Valentine photo right

 

The title of the slide below Rotomahana Looking to Site of Pink Terrace, indicates a view towards the former terrace, or perhaps close to it, in the aftermath of the eruption. If the location is correct, the image is important because it shows that destruction of the Pink Terraces was complete. The Mounds of volcanic ash cover almost everything. Characteristic erosional rills suggest rain soon after the eruption, where surface water run-off redistributed the ash (probably towards the lake).  I could not determine who the photographer was.

Whinfield’s slides, recently brought to life, are delighting and informing audiences today, just as they must have done when he presented them to an eager 19th century public. These days we never think twice about the projection media at our fingertips. It seems almost to be part of our subconscious, but to Whinfield’s audiences there must have been a sense of excitement, awe, and puzzlement, not just in the images they were seeing, but the fact they were seeing them at all. The havoc wreaked by distant volcanic eruptions, was delivered to their living rooms by a rapidly developing technology.

The Whinfield Terrace collection may not contain photographs of his own taking, but this is not important. An iconic landscape was taking shape in people’s minds, a narrative in images. Folk who may never have left their own village became informed; witnessing the real world shaped by unimaginably ferocious forces – a kind of 19th century Scicomm.

 

I would like to hear from anyone who has additional information on the images in Whinfield’s slides, particularly information relating to the original photographers.

 

Credits: The Whinfield collection is owned by the Worcester Diocesan Church House Trust. I am grateful to the Trust for permission to use the digital images of the slides. Thanks also to Justin Hughes of the Worcestershire Archive and Archaeology Service for bringing the slide collection to my attention, for arranging to forward the images, and for his patience with my incessant questions.

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Atlas of volcanoes and volcanic rocks

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Volcanoes and the products of volcanism

The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source as indicated below (it is the polite, and professional thing to do).  I retain copyright of all images presented herein

Brian Ricketts –  www.geological-digressions.com

Volcanoes shape our earth: landscapes, the air we breathe, the oceans.  From day one they have had a direct influence and impact on life itself.  They still occupy a central place in our daily lives. Recent events in Hawaii (fissure eruptions, May-June 2018) and the explosive eruption of Fuego with its destructive pyroclastic flows (Guatemala, June 2018), have killed local inhabitants and destroyed property. Social media makes sure that we are kept up to date with these events; the fourth estate makes sure we are regaled with the death and mayhem.

I have never seen an actual eruption; the inquisitive, scientific part of me would love to witness one (at a safe distance). On my doorstep are three extinct stratovolcanoes 2-3 million years old. An hour and a half drive south puts me smack in the middle of the Taupo Volcanic Zone that, historically and prehistorically, is prone to cataclysmic, explosive fits. The same travel time north and I’m in the Auckland volcanic field, the most recent eruption of which was about 600 years ago. But I have seen the products of volcanism – the quiet effusive type, explosive and cataclysmic events; some as old as 2 billion years, others much more recent.

The collection of images here is a sample of these events. Some I have published, others just visited. I include this category in the Atlas because volcanic edifices and eruption products have a significant impact on sedimentary basins, and provide large volumes of sediment that ultimately are distributed throughout terrestrial drainages systems and marine environments; volcanoes contribute to sediments and sedimentary environments.

There are lots of good sites detailing volcanoes and eruptions. One of my favourite sites for volcano updates is Voices of Volcanology – Facebook @VoicesofVolcanology

Its contributors also provide a rational response to some of the silly, sometimes dangerous media hyperbole.

The USGS also provides media, scientific, and activity alert updates for many volcanoes around the world. One that I keep tabs on (for obvious reasons) is the NZ volcano scene

Click on the image for an expanded view, then ‘back page’ arrow to return to the Atlas. Use the following links to jump to specific image sets:  Precambrian  Arctic

New Zealand  Hawaii  Haleakala

This link will take you to an explanation of the Atlas series, the ownership, use and acknowledgment of images.  There, you will also find links to the other Atlas categories.

 

The images:

Paku Rhyolite dome

Paku rhyolite dome, guards the entrance to Tairua Harbour and estuary, east Coromandel Peninsula, New Zealand. The Paku eruptive center was part of widespread rhyolitic and dacitic volcanism from Late Miocene to Early Pleistocene in the Coromandel Volcanic Zone. They are part of the Minden Rhyolite Group. Paku is about 7-8 million years old (Pliocene). The Paku hypersthene-hornblende-biotite rhyolites here are beautifully flow banded and spherulitic,

             

 

             

 

            

 

Garibaldi Volcanic Field

The Garibaldi and Garibaldi Lake volcanic fields contain some of the youngest eruption products in Canada; most of the activity is about mid-Pleistocene through Holocene.  Most common are calc-alkaline andesites and dacites, with some basaltic rocks, associated with subduction of the Juan de Fuca Plate. They are located 60-70 km north of Vancouver. Mt. Garibaldi is a stratovolcano, with foundations as old as 1.3 Ma; Black Tusk also has old volcanic foundations, but its present form is due to much younger activity.  Late Pleistocene activity took place beneath the western segment of the Laurentide-Cordilleran Ice Sheet.

Herein are a few images of Garibaldi, Tusk, and Garibaldi Lake (the latter is a really nice hike).  Images of lava flows are from exposures along Highway 99 between Squamish and Pemberton.

                 

Lake Garibaldi. Sub-glacial andesite flows in the foreground

 

             

Black Tusk is the remains of an eroded stratovolcano whose foundations erupted about 1.3Ma. Rocks forming the present pinnacle were erupted about 200,000 years ago. This dome was subsequently eroded by the Cordilleran Ice sheet.  Left: from the Callaghan River access road. Right: From Brandywine Falls lookout.

 

          

A tiered, columnar jointed flows overlying Coast Mountain granodiorite. About 10 km north of Squamish, on Highway 99

 

          

Jointed andesitic-dacitic overlying pre-existing, sub-glacial topography on eroded Coast Mountains granodiorite and metamorphic rocks. The contact is shown in red on the left image. Right image: detail of the bedrock, that here contains structurally interleaved and sheared granodiorite and amphibolite. About 10km north of Squamish, Highway 99.

 

                       

 

About 15 km north of Squamish on Highway 99; this jointed lava flow has over-ridden dacitic agglomerate. The flow base is lined with abundant vesicles, most of which have been stretched approximately parallel to the basal flow contact.  The flow base is highly irregular, possibly following sub-glacial erosional topography.

 

                           

Same lication as above. The basal agglomerate here appears to be part of the original flow unit, where the lower cooled lava has been fragmented by the moving flow. Some fragments have been reincorporated into the base of the solid flow.

Precambrian volcanics

This set of images is from the Proterozoic Flaherty Formation, Belcher Islands. A small number of Rb/Sr and Pb-Pb ages indicate between 2.0-1.9 billion years. The Flaherty succession consists of interleaved tholeiitic to subalkaline basalt flows, pillowed lavas, pyroclastic and/or density current ash flows, and interflow turbidites, that accumulated mostly in a marine environment, although edifices may have extended above sea level. Metamorphism is prehnite-pumpellyite grade, and preservation of primary volcanic and volcaniclastic structures is excellent.  The volcanics were extruded on Proterozoic continental crust. However it is still uncertain whether they represent some kind of mantle plume, or formed during extension associated with crustal flexure, or are a hybrid of continental arcs.

              

Jointed lava flows and wrap-around piles of pillow lavas on Flaherty Island. Outcrops often permit the 3-dimensional geometry of flows and pillows to be mapped.

An interpretation of interleaving flows and pillowed lavas, and associated volcaniclastics. The figure is from a 1982 paper: Volcaniclastic rocks and volcaniclalstic facies in the Middle Precambrian (Aphebian) Belcher Group, Northwest Territories, Canada. Canadian Journal of Earth Sciences, v. 19, p. 1275-1294. 

 

 

              

Spheroidal, lobate, and lozenge-like pillow lavas. Left: the main pile is overlain and partly amalgamated with a second pile (top to the right), separated by a layer of glassy fragments formed by thermal shock. West Flaherty Island. Right: Oblique section through pillows, shows chilled margins with small vesicle traces (formerly gas bubbles).

 

                

Surface structures on pillows. Left: small ropy festoons. Right: crudely polygonal crusts formed by rapid cooling in the Precambrian ocean.

 

              

Left: Lozenge-shaped pillows with central flat-bottomed gas cavities, now filled with coarse calcite and prehnite crystals. Right: Filling of a pillow interstice with a layer of shards formed by thermal shock, overlain by coarse calcite. Look closely and you will see the first generation calcite grew in radial clusters on the pillow margin.  Both structures (also called geopetal structures) are useful for determining stratigraphic way-up (top).

 

             

Small lava tube that acted as a feeder to the pillow lavas. Lava in the tube must have drained, leaving an open tube that subsequently was filled by very coarse calcite crystals.

 

A recent lava tube breakout on Kamokuna lava delta, November 2017, Hawaii. This example is on land, but serves as a useful analogy to the submarine lava tube in the image immediately above.

 

 

 

              

Two perspectives of the tops of lava flows. Left: A bedding view (looking down on the flow top) of brecciated, folded and generally squished basalt fragments that formed as the flow cooled, and were carried along the top of the flow. The oblique grooves across the rock face were formed by glacial scouring.  Right: Cross-section through a lava flow; the upper part is completely broken up by movement as the lava solidified. More coherent, less fragmented rock occurs below this (lower right), was deeper in the flow and cooled more slowly.

 

More fluid lava flows formed ropy festoons. Here, flow direction was approximately to the lower right.

 

 

 

              

The base of a lava flow will also cool more quickly, especially if sediment or rock beneath is wet. Cooling here has resulted in rapid expansion of gas bubbles, (probably steam) that have risen into the flow forming elongated, sub-vertical, worm-like cavities, or spiracles. On the right, a larger gas bubble has risen above the flow, and subsquently evolved gas into small cavities in a crude radial pattern (arrow).

 

Larger gas cavities (vesicles) also form within the flow masses, as volcanic gas (water, CO2, SO2) separates from the melt. Here, the cavities are surrounded by much smaller vesicles.

 

 

 

Upper contact of a massive sediment gravity flow. Framework clasts up to a metre are mostly volcanic, but there are a few ripped up sandstone and dolomitic sandstone clasts, presumably from units underlying the Flaherty Formation. Maximum thickness is 85m; the unit covers and area greater than 3000 sq km. There are no obvious depositional or erosional breaks within the unit; there are parallel laminae, and rare crossbeds. The framework is mainly pumice fragments, shards with bubble-wall texture, and lapilli (see photomicrographs below). Pumice generally increases towards the top – density grading, but no obvious size grading. It is not welded.  It is sandwiched between pillowed and jointed lava flows.  It was most likely deposited subaqueously, although it is also possible that the flow originated on a subaerial edifice. Parallel laminae may indicate a degree of surging.  The irregular surface patterns are due to late diagenetic silica replacement of the original volcanic glass.

 

                               

 

Photomicrographs from the massive volcaniclastic flow. From the Left: 1. pumice with elongate gas pores, and various shards (glass replaced by silica). Field of view 8 mm.  2 Shards and lapilli. Both cements are coarse calcite, that has also replaced some matrix. Field of view 8 mm.  3. Bubble-wall ash shards, pumice and matrix in finer-grained part of the flow unit. Field of view 3 mm. 4 Fine, distal flow unit, predominantly bubble-wall shards, some pumice, and basalt fragments.  Field of view 8 mm.

 

              

Inter-flow volcaniclastic turbidites, layers of air-borne ash into water, and hemipelagic mudrock and ash. Right: detail of thin graded volcaniclastic turbidite Tb-d beds, hemipelagic ash, and highly calcareous mudstone – the latter indicating periods of very slow clastic deposition.

 

              

Left: Laminated and rippled volcaniclastic sandstone-siltstone. The middle bed has several load casts. Right: Volcaniclastic sandstone with ripples and climbing ripples. Bedforms in the upper orange-brown layer resemble antidunes.

 

              

Left: Graded volcaniclastic turbidite (Tb-d divisions), in erosional contact with a (steel grey), muddy limestone calcareous mudstone. Right:Laminated and convoluted volcaniclastic Tc-d turbidite intervals. The middle graded bed truncates  the convolutions below.

 

              

Left: Photomicrograph of turbidite volcaniclastic sandstone. Clear bubble-wall textures, some pumice, and crude alignment of shard long directions. Field of view 3 mm. Right: Prehnite in very fine-grained basalt. Field of view 3 mm.

 

Arctic

              

Strand Fiord volcanics, an Upper Cretaceous unit on Axel Heiberg Island, Canadian Arctic. Here an ‘organ-pipe’ array of columnar joints (4m high) have perforated the basalt during cooling. On the right, a bird’s-eye view of 4, 5 and 6-sided columns.

 

              

Curved and radiating entablature joints in Strand Fiord basalt flows, Axel Heiberg Island. Structural dip here is about 60 degrees. Flow thickness is about 35m. The entablature on the left is underlain by bed-normal jointed basalt.

 

              

Left: Cow pat ballistics in bedded lapilli and reworked basalt gravel, attests to eruption material mixing directly with fluvial reworked debris. The right image shows a coalified tree fragment caught up in a lahar. Strand Fiord volcanics, Axel Heiberg Island.

 

              

The Mount Edziza volcanic field in Stikine, northern British Columbia began 7.5 million years ago, and continued into the Pleistocene. It features large stratovolcanoes, calderas and cinder cones. Featured here is a stairway of jointed basalts, and a well preserved cinder cone.

 

New Zealand

                            

 

Upper Miocene Coroglen volcanics north of Whiritoa,  east coast of Coromandel, New Zealand. From the left: 1. Cooling joints in ignimbrite. 2. Detail of ignimbrite fragmental pumice and rhyolite, and fiamme (dark fragments stretched during hot emplacement of the pyroclastic flow).  3. Flow banded rhyolite. Outcrop is about 5m high.  4. A lahar with fragments of rhyolite, ignimbrite and possible andesite, over-ridden by a flow-banded rhyolite.

 

              

Late Pliocene flow-banded rhyolite at Mount Maunganui, New Zealand.

 

                              

 

Karioi volcano, Raglan New Zealand.  A Late Pliocene stratovolcano that during eruptions and later formation of lahars, dipped its toes in Tasman Sea. Three images from the left show an upper andesite flow, over airfall lapilli tuffs, and at base a laharic breccia.  On the right, detail of lapilli tuffs with a larger ballistic clast (20cm long).

 

                            

 

Stream reworking and lahars from the flanks of an active Karioi volcano, delivered pebble to boulder sized debris to the Late Pliocene coast. Evidence for this is seen in pockets of fossil molluscs (mostly bivalves) – modern bivalves commonly are wedged between clasts – these are not fossils. Rounding of clasts probably took place in streams and during coastal reworking. A few large boulder rafts are 3-4m across.

 

Auckland volcanic field contains about 50 known eruptive centres; scoria cones, lava flows,  and craters formed by highly explosive, phreatomagmatic eruptions, concentrated in an area of metropolitan Auckland, about 360 sq km. Activity began about 250,000 years ago; the youngest is Rangitoto which erupted 600 years ago, and was witnessed by Auckland Maori.

             

Eruption of Rangitoto in Auckland Harbour produced a circular island. The central scoria cone is flanked by aa basalt flows, air-fall scoria and lapilli. In the left image, In the left image (viewd from Musik Pt.), Motukorea (also known as Brown’s Island) is a small cone, thought to have erupted 7000-9000 years ago. Right image from Motuihi Island.

 

                           

 

Rangitoto features: From the left: Blocky and rubbly aa flows; a lava cave, and a profile of weathered lapilli.

 

                          

Explosion craters, or maars. Lake Pupuke, now filled with a fresh water lake is more than 45,000 years old. Orakei Basin (centre) is tidal – more than 83,000 years, and Panmure Basin (right), also tidal, is older than 17,000 years. The crater entrance is a narrow rocky channel, connected to Tamaki estuary – this is the Pacific Ocean side of Auckland. The stretch of water in the distance is part of Manukau Harbour – the Tasman Sea side of Auckland. A narrow isthmus separates the two ocean water bodies.  All three craters are rimmed by tephras. Lake and tidal basin sediment fill can also be used to date the events, using pollen and ash layers derived from more distant eruptions in Rotorua-Taupo.

 

                          

 

           

This group of images shows well bedded air-fall tephra layering near the outer rim of Maungataketake maar volcano, bordering Manukau Harbour, west Auckland. It is close to Auckland International Airport. Age is uncertain but could be as old as 177,000 years. Layers were also disrupted by ballistics (bomb sag, 3rd from left).  The eruption apparently obliterated a nearby forest – ash layers drape a stump (4th from left), and in the modern shore platform, large tree trunks were flattened.

 

                         

 

Mt Taranaki (Egmont), is an andesitic stratovolcano that began erupting 130,000 years ago. It is  regarded as active. The edifice is surrounded by a spectacular ring plain, dotted with lahar mounds, testament to the destructive nature of volcanoes even when not erupting. The lahars were generated on the volcano flanks during large landslides, including possible sector collapse; loose rock, mud and water form fluid, fast-moving flows. They can travel many kilometres from their source.  Conical lahar mounds commonly form around very large rafts of rock (sometimes many metres across), once the flow has come to rest.  Images on the right show typical, poorly sorted lahar textures.

 

                           

West of Auckland city, Waitakere hills are underlain by Early Miocene andesitic and basaltic flows, pillows, and debris flows, derived from volcanic centres off the west coast of New Zealand. Marine fossils are commonly caught up in the lahars and debris flows. Typical debris flow textures shown on the left; centre cliff with many stacked debris flows) boulders up to 1.5m wide), intruded by a dyke – Karekare Beach. Right image shows two, very large lava tubes, filled with radially jointed andesite (Maori Bay), feeders from nearby Waitakere Volcano.

 

                           

Conical mounds on Mamaku Plateau, north of Rotorua, look superficially like lahar mounds. However, in this case the mounds formed from a hot ignimbrite (240,000 years ago) with preferential cementation and welding by hot gases.  Subsequent erosion has left the harder zones upstanding (also called Tors).  The image on the right shows this hard, central zone. (located on State Hwy 5)

 

                         

A Mamaku Plateau mound with central cemented, resistant hard core (a remnant of the Mamaku Plateau Ignimbrite), draped by air-fall tephra.

 

             

Mt Ngauruhoe (aka Mt Doom) is a stratovolcano, and the youngest component of the Tongariro volcanic complex. It may be as old as 7000 years. It is made up of andesite flows, scoria and ash. Several young lava flows extend into adjacent Mangatepopo Valley.

 

             

Left: Typical scoriaceous aa flow in Mangatepopo Valley. Right: Looking down the path of a pyroclastic flow generated during the 1975 eruption. The flow contains a chaotic jumble of scoria and ash, with blocks up to 2m across. In place there are distinct rubbly levees. The flow rode over part of an older lava flow – the darker grey area, upper middle of image.

 

Hawaii

              

Halemaumau crater, Kilauea as it was in 1983. It looks very different now!

 

             

Left: Lava tree, cast during a 1790 eruption. Right: A nice sea arch eroded into layered flows.

 

             

Left: Spatter on a small lava tube vent, Kilauea. Right: Pelee’s Hair – volcanic glass that has been stretched while molten.  The preservation potential of such structures is very low.

A small flow with ropy central portion and raised levees of fragmented basalt.

 

                          

 

Ropy lavas, festooned, twisted, knot-like, and folded. Kilauea

 

Haleakala crater, Maui

A large stratovolcano that last erupted about 500 years ago

                          

From the summit (a little over 3000m) climb down to the crater floor to a parched landscape of cinder cones, crunchy lapilli underfoot, and a myriad ballistics. The crater walls (centre) exposes multiple episodes of dyke intrusion that fed the overlapping scoria mound conduits.

 

                          

Ballistics: left is a flattened cow pat splatter. Centre a spindle bomb, twisted in flight. Right bread-crust cooling pattern on a flattened bomb.

 

Hardy Silver Swords. Spikey

 

             

Oxidised air-fall lapilli and ash layers on older flanks of the Haleakala Volcano

 

 

 

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Hiking with my grandson

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Version 1:
“What’s that Pa?”
Point it out, the “What’s that”.
Ah yes, I see what you’re at.
That is that, and this is that.
It’s all to do with…
geological this and thats.
An erupting this over here, and
A gurgling that over there.
“Thanks Pa”.

Version 2:
So mate there’s another of those
recent lava flows.
Vesicular scoria atop aa!
Yep, that’s it mate.
You can tell this one’s older than that one,
because
it has more vegetation (you figured that out,
good one mate), and
the younger flow crept up over the older one.
That’s called Superposition  – will you
remember that for next time mate?
Very important geological principle.
“Yes Pa” (looks in the opposite direction )

And this mate, a bit scary –
Some volcanic rabble rouser tossed this down the flank.
Clouds of gas and lava bits n pieces, churning,
smothering.
No getting away from that one mate – that pyroclastic flow.
Might pay to remember that as well, eh!

Back home:
Nonnie asks “how was that?”
“Really cool. I learned about…
vehicular lava,
some arcane rule about the preferred position,
and when volcanoes are in a bad mood, lots of gas “.

Nice re-cap mate!

Tongaririo Crossing, in Tongariro National Park, is one of New Zealand’s most popular hikes – a good 7 hours to do the complete trail, complete with elevation gain, fumaroles, craters, cold wind. and the ever-present risk of an eruption.  Seriously worth the effort.

The Park is a World Heritage Site. It is centered around the three active volcanoes, Ruapehu, Tongariro, and Ngaruahoe.

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Deciphering a volcano’s moods; predicting volcanic eruptions

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A peaceful morning, zephyrs, whispy clouds wrapping, scarf-like, the towering edifice that is your town’s backdrop. A sudden roar; the clouds are shredded.  The turmoil of a volcano with attitude, a billowing column of ash and rock, tossed effortlessly skyward, reaching heights of 5 to 7 km in a matter of minutes. Not content with this scene, parts of the column collapse into fast-moving, ground-hugging pyroclastic flows that smother and incinerate everything in their path. This was Sinabung a few days ago (February 19, 2018 – the Youtube video is worth watching).

The Indonesian volcano is regarded as active and has been erupting off and on for about 7 years, following a 400-year slumber, although the violence of this event caught many by surprise. Happily, it was short-lived and no lives were lost. But the event does illustrate the fickleness of volcanoes, and like a case of indigestion, a bad-tempered, frequently unpredictable response to rumblings in their internal plumbing. Eruption prediction ideally should provide sufficient warning to all those who live nearby; Sinabung decided otherwise. Continue reading

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Erupting mud volcanoes; We have ignition

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Mud
It supports geological processes.
It flows, subsides, and leads to failure, sometimes catastrophically.
It can be beneficial, forming fertile river floodplains.
It can be a pain in the neck, clogging infrastructure.
It oozes when soft; dries brick-hard
People bathe in it. Pigs love it.

And it erupts, as volcanoes.

Not the magmatic kind, with 1000oC lavas or explosive ash columns, but eruptions nonetheless. Most mud volcanoes are much smaller than their magmatic counterparts; some only a metre high, others 10s of metres. Eruptions may be the quiet, oozy kind where mud flows, slithers and slides down slope, or more violent, shooting sticky stuff 10s of metres into the air (or water); some even ignite in a cascade of fireballs. And yes, they do form on the sea floor.  One example in 2015 along the Sea of Azov coast (land-locked between Russia and Ukraine), sent mud and water several metres into the air; you can see the muddy jetsam gradually expanding across the sea surface.  Continue reading

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Ropes, pillows and tubes; modern analogues for ancient volcanic structures

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Analogies are the stuff of science. In geology, we frequently employ modern analogies of physical, chemical, or biological processes to help us interpret events that took place in the distant past. We cannot observe directly geological events beyond our own collective memory. Instead, we must infer what might have taken place based on evidence that is recorded in rocks, fossils, chemical compounds, and the various signals that the earth transmits (such as acoustic or electrical signals).  Analogies are not exact replicas of things or events, although they may come quite close. Their primary function is to guide us in our attempts to interpret the past.  As such, they are part of our rational discourse with deep time. Analogies are at the heart of the concept of Uniformity espoused by our 18th and 19th century geological heroes, James Hutton and Charles Lyell; they are the foundation for the common dictum “the present is the key to the past”, coined by Archibald Geikie, an early 20th century Scottish geologist.

Even though lots of people have written about this, I figure one more example that illustrates the methodology won’t hurt. Forty years ago, I worked on some very old rocks on Belcher Islands, Hudson Bay, that included volcanic deposits. Looking at the photos (35mm slides), I still marvel at the geology, the fact that something almost 2 billion years old is so well preserved, makes it look like the volcano just erupted.

Here are three ancient structures that were constructed by flowing basalt lava. Each can be compared with modern volcanic structures and processes that we can observe directly.  We can interpret the ancient structures according to the similarities and differences between the modern analogues and the ancient versions. The examples are from strata known as the Flaherty Formation, a succession of volcanic rocks exposed on Belcher Islands, Hudson Bay. Continue reading

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Islands with attitude; the devastation wrought by collapse of oceanic volcanoes

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Krakatoa, 1883, and the seas shivered. The eruption, one of the largest in recorded history, delivered tsunamis that swept away entire villages around Indonesia and its neighbours; little more than the flotsam and jetsam of nature’s fickleness.  Five years later, in the same general neighbourhood, nature was at it again.

Ritter Island, barely a speck on most maps, is a volcanic edifice rooted to the floor of Bismarck Sea between Papua New Guinea and New Britain. In 1888, most of the island slid beneath the waves, creating avalanches of rocky debris.  Eye-witness accounts tell of multiple tsunamis over a 3-hour period, and waves at least 8m high with run-ups to 15m above sea level.  Ritter Island is an active volcano, but at that time it was not erupting in any major way.  The island landslide is probably the largest in recent history – more than 4 cubic kilometres of volcanic rock were dislodged and redeposited along the seafloor. Slope failures like this are called volcanic sector collapses. Continue reading

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Lahars; train-wreck geology

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Christmas morning in New Zealand is synonymous with mid-summer barbecues at the beach, deservedly lazy times, perhaps a bit of over-indulgence. That morning, in 1953, Kiwis were expecting to awaken to news of the Royal tour; the newly crowned Queen was doing the rounds of towns and countryside, perfecting that royal wave to flag-waving folk lining the streets. Instead, they awoke to the news of a train disaster near Mt. Ruapehu, one of three active volcanoes in central North Island; a railway bridge on Whangaehu River, near Tangiwai, had been washed out on Christmas Eve.  Train carriages were strewn along the river banks, 151 people were killed.  The culprit was a geological phenomenon known as a lahar. Continue reading

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Overture to a cave; the spectacle of jointing in ancient basalt lava flows

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Saturday August 8, 1829, Felix Mendelssohn and his traveling companion Karl Klingemann, took a boat trip to Fingal’s Cave, the entrance to a world beneath Staffa, an inconspicuous dot on the edge of the Atlantic. Staffa is part of the Hebrides Archipelago, west Scotland. Celtic legend called it Uahm Binn, ‘The Cave of Melody’, that in story was part of a bridge extending to the iconic Giant’s Causeway in County Antrim (Northern Ireland).  The Celtic name is apt; Atlantic swells echoing countless songs.  Klingemann later wrote “Fingal’s Cave…its many pillars making it look like the inside of an immense organ, black and resounding, and absolutely without purpose, and quite alone, the wide grey sea within and without.”. Continue reading

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Io; Zeus’s fancy and Jupiter’s moon

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Zeus, the head-honcho of assorted Greek gods, heroes, nymphs, and mortals, was chiefly the God of the Sky, or Heavens. One of his minor portfolios was the upholding of Honour, but as mythology relates, he didn’t put much energy into that particular task; he was a philanderer, much to the annoyance of his own wife, Hera (I guess his energies were directed elsewhere).  One such misdirection was Io, a mortal woman, who had the misfortune to be turned into a heifer by Zeus, to hide the infidelity from Hera. Io’s memory now survives as a planetary body; one of the Galilean moons of Jupiter is named after her (to be named a moon of the Roman God Jupiter, seems like a historical slap in the face to the Greek deity). Continue reading

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