This 1783 Volcanic Eruption Changed The Course Of History

“The sun fades away, the land sinks into the sea,the bright stars  disappear from the sky,
as smoke and  fire  destroy  the world,
and the flames reach the sky.”
The End of the World according to the “Völuspa“, a collection of Icelandic myths compiled in the 13th century.

June 8, 1783 marks the beginning of a volcanic eruption that will change history…

April 18, 1906: San Francisco´s Wicked Ground

“O, promised land
O, wicked ground
Build a dream
Tear it down

O, promised land
What a wicked ground
Build a dream
Watch it all fall down”
“San Andreas Fault”

Sailors on board of the “Wellington“, just entering the bay of San Francisco, noted something unusual in the early morning hours of April 18, 1906. The captain reported later that the ship “shivered and shook like a springless wagon on a corduroy road” even if the sea was as “smooth as glass.“

Clarence Judson was swimming near Ocean Beach when he suddenly was pulled by a strong current into the sea. He made it back to the shacking shores.

“I tried to run to where I left my shoes, hat and bathrobe ... but I guess I must have described all kinds of figures in the sand.“

In Washington Street, police sergeant Jesse Cook observed a terrifying spectacle:

“The whole street ... It was as if the waves of the ocean were coming towards me,  ...[]... Davis Street split right open in front of me, []… A gaping trench. . . about six feet deep and half full of water. Suddenly ...[]... the walls of the building began to shake. Before I could get into the shelter of the doorway the walls had actually fallen inward.“

George Davidson, professor for Geography, woke up from the tumult coming from the streets. He grabbed his watch on the desk and noted the length of a first quake – 60 seconds – followed by a second – again 20 to 40 seconds long. His observations – 5:12am in the morning – will later be used to determinate the official time of the great earthquake of San Francisco. Many people were still asleep and killed in their beds, those who escaped gathered in the streets. Despite the earthquake, most of the city seemed still intact and surprisingly quiet.
In 1906 San Francisco was already considered a great, but also corrupt, city with more than 400.000 inhabitants. Thanks to the discovery of gold in the rivers of California the city was quickly expanding into its surroundings. It was an important gateway to the Pacific and a modern trade place. The newest technology in film equipment was available in the shops. The earthquake of San Francisco will become the first natural disaster of this magnitude to be so well documented by photographs and film footage (even in color).
However, most buildings in San Francisco were poorly constructed and made of wood. San Francisco had burned to the ground six times in the past century and experienced strong earthquakes in 1865 and 1868, when 30 people were killed.

“Earthquakey Times“, a caricature by Ed Jump of the October 8, 1865 earthquake in San Francisco. While he was working as a newspaper reporter in San Francisco, Mark Twain experienced the earthquake which he describes in his 1872 book “Roughing It.” – “It was just after noon, on a bright October day. I was coming down Third Street. The only objects in motion anywhere . . . were a man in a buggy behind me, and a [horse-drawn] streetcar wending slowly up the cross street. . . . As I turned the corner, around a frame house, there was a great rattle and jar. . . . Before I could turn and seek the door, there came a terrific shock; the ground seemed to roll under me in waves, interrupted by a violent joggling up and down, and there was a heavy grinding noise as of brick houses rubbing together. I fell up against the frame house and hurt my elbow. . . A third and still severer shock came, and as I reeled about on the pavement trying to keep my footing, I saw a sight! The entire front of a tall four-story brick building on Third Street sprung outward like a door and fell sprawling across the street, raising a great dust-like volume of smoke! And here came the buggy-overboard went the man, and in less time than I can tell it the vehicle was distributed in small fragments along three hundred yards of street. . . . The streetcar had stopped, the horses were rearing and plunging, the passengers were pouring out at both ends. . . . Every door, of every house, as far as the eye could reach, was vomiting a stream of human beings; and almost before one could execute a wink and begin another, there was a massed multitude of people stretching in endless procession down every street my position commanded. . . . For some days afterward, groups of eyeing and pointing men stood about many a building, looking at long zig-zag cracks that extended from the eaves to the ground...”

Police sergeant Jesse Cook was the first person to report a fire in a grocery in Clay Street. An hour later there were already fifty fires spotted in the entire city. The firefighters realized horrified that the water pipes in the underground were broken and the hydrants useless. The resulting firestorm will burn three days and will destroy 90 percent of the 28.000 buildings in San Francisco.

Journalist Arnold Genthe will take one of the most famous photos in history. 

“I found that my hand cameras had been so damaged by the falling plaster as to be rendered useless. I went to Montgomery Street to the shop of George Kahn, my dealer, and asked him to lend me a camera. “Take anything you want. This place is going to burn up anyway.” I selected the best small camera, a 3A Kodak Special. I stuffed my pockets with films and started out….”

“Looking Down Sacramento Street, San Francisco, April 18. 1906“, photography by Arnold Genthe.

In Jackson Street, the owner of the “Hotaling´s Whiskey” distillery decides to fight the flames. He pays 80 men to sprinkle 5.000 barrels of whiskey with water pumped out from the sewer system. Later he will mock all those who claim that the earthquake was sent by god by coining a new advertising slogan for his company.

“If, as some say, God spanked the town, for being over frisky – why did He burn the churches down and save Hotaling´s Whiskey?“

Army troops were soon ordered into the city to help the firefighters and prevent panic and looting. Despite the fact that martial law was never proclaimed, the major authorized policeman and soldiers to shoot looting persons – “Obey orders or get shot” was the grim warning on the signboards.
Guion Dewey, a businessman from Virginia, wandering the streets of downtown San Francisco minutes after the quake, experienced the best and worst of human behavior, as he later wrote in a letter to his mother:

“I saw innocent men shot down by the irresponsible militia. I walked four miles to have my jaw set. A stranger tried to make me accept a $10 gold piece. I was threatened with death for trying to help a small girl drag a trunk from a burning house, where her father and mother had been killed. A strange man gave me raw eggs and milk . . . (the first food I had had for twenty-two hours). I saw a soldier shoot a horse because its driver allowed it to drink at a fire hose which had burst. I had a Catholic priest kneel by me in the park as I lay on a bed of alfalfa hay, covered with a piece of carpet, and pray to the Holy Father for relief for my pain. . . . I saw a poor woman, barefoot, told to “Go to Hell and be glad for it” for asking for a glass of milk at a dairyman’s wagon; she had in her arms a baby with its legs broken. I gave her a dollar and walked with her to the hospital. . . .I was pressed into service by an officer, who made me help to strike tents in front of the St. Francis Hotel when the order was issued to dynamite all buildings in the vicinity to save the hotel. I like him and hope to meet him again. When he saw I was hurt, which I had not told him, not yet having been bandaged, he took me to his own tent and gave me water and brandy and a clean handkerchief.“

The earthquake and the firestorms killed an estimated 3.000 to 4.000 people, destroyed 28.000 buildings and the infrastructure of the entire city. However, thanks to a quick rebuilt, just three years later most of San Francisco looked as if the earthquake never happened.

Seismology was still a young scientific discipline at the time of the earthquake in San Francisco. Worldwide there were only 96 seismographs operating, none of these in California. In the aftermath of the disaster, only three days later, the Governor of California announced the formation of the State Earthquake Investigation Commission, led by geologist Andrew C. Lawson of the University of California.
The commission focused on the San Andreas Rift, a nearby valley until then considered of minor interest and mapped geologically only in short sections. For two years Lawson and his team followed the rift, mapping ponds, streams and hills on foot and horseback. They recognized that the rift follows almost the entire coastline of California for more than 1.000 kilometers. During the April 18, earthquake, almost 480 kilometers of this large fault suddenly ruptured, displacing large sections horizontally, not vertically, as geologists had previously believed to be the source of earthquakes. The commission discovered that earthquakes can be generated also along so-called strike-slip faults.
The epicenter of the earthquake was at first located at the point with the largest observed displacement on land. However, today the epicenter is believed to be situated in the Pacific Ocean, in accordance with the seismic waves coming from the sea as observed by the first eyewitnesses.
The results of the scientific investigation of the San Francisco earthquake led Henry Fielding Reid, a geology professor at Johns Hopkins University in Maryland, to propose a new theory regarding the origin of earthquakes, later dubbed the “theory of elastic rebound“. Reid’s hypothesis will have a revolutionary impact on the young science of seismology.

Sources:

SLAVICEK, L.C. (2008): The San Francisco Earthquake and Fire of 1906. Great Historic Disasters. Chelsea House Publishers: 128
STARR, J.D. (1907): The California Earthquake of 1906. A.M. Robertson, San Francisco

Clash of the Titans: The Science behind the Iceberg that sank the Titanic

The tragedy of the “unsinkable” Titanic – lost in the cold water of the Atlantic – became part of history and pop culture, but the story of the main culprit that caused the disaster is mostly forgotten and only vague descriptions and some photos exists of the supposed iceberg(s). One famous photography taken from board of the cable ship “Minia“, one of the first ships to reach the area in search for debris and bodies, shows a tabular iceberg, an unusual shape for icebergs in the northern Atlantic. The crew found debris and bodies floating in the vicinity and the captain assured that this was the only iceberg near the point of the collision. However most surviving Titanic testimonies described later the infamous iceberg with a prominent peak or even two.

Fig.1. The moment of the collision according to the sailor Frederick Fleet - one of the two men on duty as lookout in the night of the disaster (after EATON & HAAS 1986).

Fig.2. Journalist Colin Campbell, a passenger of the "Carpathia" - the first ship to approach the scene of the disaster the next morning and save the surviving passengers of the Titanic - described the iceberg for the "New York Tribune" (after EATON & HAAS 1986).

Fig.3. One of the many icebergs photographed in the morning of April 15, 1912. The passengers on the ship “Prinz Adalbert”, still unaware of the disaster of the previous night, reported later to have noted a “red smear” at the waterline of the white iceberg.

Fig.4. Photography of an iceberg from the cable ship "Minia", one of the first ships to reach the area in search for debris and bodies. The crew found debris and bodies floating in the vicinity of the depicted iceberg and the captain assured that this was the only iceberg near the scene of the collision (after Titanic & Nautical Resource Center).

Fig.5. Another iceberg, photographed five days later from board of the German ship “Bremen”, claimed to be the Titanic iceberg based on the vicinity to the location of the disaster and the description of the iceberg according to survivors. An "authentic" photography of the iceberg that sank theTitanic was worth a lot of money for the eager press, this also explain why so many photographs of icebergs were taken at the time.

Fig.6. Photography taken from board of the ship “Birma” of the same iceberg as seen by the passengers of the “Carpathia” (see also Fig.2.) – the first ship to approach the scene of the disaster and save the surviving passengers of the Titanic – and published at the time in the “Daily Sketch”. This iceberg has in fact some remarkable similarities to the iceberg as described by survivors of the disaster.  
Despite the question if one of the photos shows really the culprit iceberg, the remarkably number of spotted icebergs emphasizes the notion that in 1912 a quite impressive number of these white titans reached such southern latitudes.

The icebergs encountered in the North Atlantic originate mainly from the western coasts of Greenland, where ice streams deliver large quantities of ice in the fjords which lead to the Baffin Bay. Every year ten-thousand of small and large pieces of ice drop from the front of the glaciers and are pushed by the West Greenland Current slowly to northern latitudes, far away from ship routes. Following first the coast of Greenland this current is diverted by the Canadian coast to the south, forming the Labrador Current that circumnavigates Newfoundland and delivers the iceberg to the warm Gulf Stream. A more than 5.000km long journey full of obstacles and incessant erosion by the sun, the water and the waves. Only estimated 1 to 2% of large icebergs will, after a period of 1-3 years, reach latitude 45°N, crossing one of the most important route for ships of the entire Atlantic Ocean.

Fig.7. Schematic map of marine currents (blue= cold; red = hot) around Greenland, probable region of origin (West Greenland) and hypothetical route of the iceberg that hit the Titanic.

Apparently in 1912 icebergs were spotted remarkably often in this region and various hypotheses tried to explain this “anomaly”.  The years before 1912 were characterized by mild winters in Europe and possibly the northern Atlantic. It was therefore speculated that the (relative) warm temperatures increased the melting rate and activity of the calving glaciers on Greenland. 
Also a strengthened Labrador Current, pushing cold water and icebergs much more to the south, was proposed to explain the ice field that in the cold night 100 years ago forced various ships to stop along the Atlantic route. 
Both  hypotheses are based on the recorded values of Sea Surface Temperature (see this diagram by the Woods Hole Oceanographic Institution), which show an alternation of a warm and cold period  in 1900-1920.
A recent hypothesis – promoted by NG – proposes that an exceptional high tide prevented much of the larger icebergs to run, as normally would happen, on ground along the coasts of Baffin Bay. However considering that this tide occurred just some months before (January 1912) and the average velocity of an iceberg is low (0,7km/h~0,6mph), the Titanic iceberg had to take a straight course to arrive in time for his rendezvous with history – April 14, 1912.

Based on iceberg counts along the shores of Labrador and later in the Atlantic, also the year 1912 don’t seem to be necessarily such an anomalous event, but the disaster raised considerably the interest (and maybe perception) of the public for icebergs.

Fig.8. Iceberg counts (estimated before 1912) at 48°N, data compiled from the International Ice Patrol Iceberg Database.

In the days after the disaster bypassing ships encountered and photographed various icebergs. Some eyewitnesses claim to have noted red paint on some of them; however there is no conclusive evidence that one of these spotted white giants is really the iceberg that sank the Titanic. At least some weeks later the culprit iceberg, captured by the warm water of the Gulf Stream, melted and disappeared forever into the Atlantic Ocean.

Bibliography:

EATON, J.P. & HAAS, C.A. (1986): Titanic Triumph and Tragedy. Haynes Publishing: 352
SOUTH, C. et al. (2006): The Iceberg That Sank the Titanic. The Natural World documentary film – BBC

Geologists in the land of the Kangaroo

Terra Australis - the southern continent had been “discovered” by Europeans already in 1606, but only in 1642 the size of the new “island” becomes clear and the first geological observations  were made only in the early 19th century.

October 1800 two ships – the “Geographe” and the “Naturaliste” – set sail from the harbor of Le Havre, France. Under the command of Captain Nicolas Baudin (1754-1803) geographers, astronomers, artists, naturalists, zoologists, botanists, and 2 mineralogists – Louis Depuch (1774-1803) and Charles Bailly (1777-1844) – were instructed to explore, map and eventually claim for France new territories of this new world. In the last moment also the young zoologist, and trained paleontologist, Francois Auguste Peron (1775-1810) joined the expedition.

The geological observations made by Depuch (died during the expedition) are known from various reports send to Baudin. Bailly will publish some notes after his return to France and Peron included his research in the official report of the expedition.

In May 27, 1801 the bare land of Cape Leeuwin was in sight and the naturalists went on land along the Wonnerup Inlet, where they collected the first specimens of Australian animals, plants and rocks.

 

Fig.1. The “Baudin” – expedition, route drawn on Louis de Freycinet´s (1779-1842) “Carte générale de la Nouvelle Hollande”, published in 1811 as part of the results of the 1800-1804 expedition.

A storm forced the men to remain on land for several days and one man died during a failed attempt to reach the ships (during the entire expedition 32 men died, 13% of the crew, a surprising low percentage considering the period). The storm separated the two ships, the “Naturaliste” proceeded to the island of Timor, a Dutch colony at the time, where the crew fell ill with Malaria and other tropical diseases. The “Geographe” approached in November 1801 the island of Tasmania, where the expedition will stay for three months.
April 1802 the “Geographe” meet the British vessel “Investigator“. The expedition of the “Investigator” will map large parts of South-Australia and prove that Australia is one large continent, not two islands separated by a sea strait, as some geographers assumed. This was a disappointing discovery for captain Baudin, as there was no apparent geographic separation between the territories already claimed by British explorers, the entire continent had to be considered of British domain.

Captain Baudin, the crew and the naturalists could now only hope to gain some fame with the scientific results of the expedition...

The geologists Depuch and Bailly used a rock classification scheme, developed by the famous French geologist Déodat de Dolomieu, with four categories. They recognized primary rocks, such as granite; secondary rocks, such as stratified sandstone and limestone; alluvium (recent deposits) and volcanic rocks, such as basalt. The presence of these rocks in Australia was an important discovery, it proved that the classification scheme developed in Europe could be applied worldwide.

 

Fig.2. Charles-Alexandre Lesueur´s and Nicolas-Martin Petit´s depiction of Van-Diemen´s-Land for the “Voyage de decouvertes aux Terres Australes“. The two young men – unskilled workers at the beginning of the expedition -  were invited by Baudin to illustrate the logbook  -  both will become the most skilled artists for animal- and plantlife of the time. The granitic rocks found on the island of Tasmania convinced Peron and the other geologists that the most ancient – the primary – rock was Granite, forming the basement of all continents.

Paleontologist Peron noted along the west coast of Australia horizontal sand- and limestone layers (the Tamala-Limestone) and concluded, based on similarities to recent sediments, that these layers were deposited along an ancient beach, implying substantial variations in the sea level during geologic time:

“One of the greatest achievements of modern geology research and also one of its most indisputable, is the certain knowledge that, in the past, the level of the sea was higher than at the present time. At almost all places in the old and the new world is the proof of this phenomenon as numerous as it is evident. Only in les Terres australes was this still to be ascertained as, by virtue of its immense areal extent, it could have proved to be an important exception to the universality of the former domination of the ocean over the land.” 

(PERON & FREYCINET 1816)

Unfortunately the return to France will be disappointing for Peron. Captain Baudin dies on the island of Timor and French authorities will show little interest in the 220.000 samples of animals, plants and rocks, the 73 living animals, 3 kangaroos, 2 emus and 3 wombats brought back to Europe.

Peron publish his report “Voyage de decouvertes aux Terres Australes” only in  1807, after a long struggle for money and dies just three years later, before the completion of the second volume. However the sea shells collected during the expedition will be studied by an important French naturalist – Jean-Baptiste de Lamarck. In 1804 Lamarck publishes his theory about the transmutation of species, based in part of the observation that the fossil shells found in the sediments of France are similar, but not identical, to shells of living molluscs collected in Australia.

 

Fig.3. Peron discovers on the shores of Tasmania a living clam with a peculiar triangular shape – Trigonia antarctica – a genus of bivalve known only from fossils found in the sediments of the basin of Paris. He notes the similarities of this living specimen with fossil specimens – an important step to consider a relationship between fossil and extant species. Image of Trigonia sp. from Cretaceous sediments of Bavaria.

Unfortunately for Lamarck – and the naturalists of the Baudin expedition – he mixed his careful observations with wild speculations. Lamarck noted variations of organisms in time, however he could not explain why such variations occur or why certain organisms went extinct or survived – apart invoking a final cause and implying a sort of supernatural scheme. Geologist Charles Darwin will later regard Lamarck’s work as “useless“...

Fig.4. Geological map by Jules Grange, published in 1850, surprisingly little was known of the geology of Australia until the 20th century.

Bibliography:

GLAUBRECHT, M. & MERMET, G. (2007): Josephines Emu oder Die Geschichte einer vergessenen Expedition. GEO Nr.6/2007: 98-122
MAYER, W. (2008): Early geological investigations of the Pleistocene Tamala Limestone, Western Australia. from GRAPES, R.H.; OLDROYD, D. & GRIGELIS, A. (eds) History of Geomorphology and Quaternary Geology. Geological Society, London, Special Publications 301: 279-293
MAYER, W. (2009): The Geological Work of the Baudin Expedition in Australia (1801-1803): The Mineralogists, the Discoveries and the Legacy. Earth Sciences History Vol.28 (2): 293-324
RUDWICK, M.J.S. (2005): Bursting the limits of time – The reconstruction of Geohistory in the Age of Revolution. The University of Chicago Press, Chicago, London: 708

"What a confusion for Geologists" - Geologizing with Darwin

The first stop of the voyage of the Beagle (1831-1836) was “Quail Island” (today Island of Santa Maria) – a small island located in the bay of Praia of the larger island of St.Jago (today Santiago, Cape Verde Islands). This visit is especially interesting as it provides some glimpses in Darwin’s geological background at the beginning of his adventure and his later “evolution” as geologist.
 

Darwin collected basic experience as geologist during a field trip across Wales and surely know the geological theories of the time, especially regarding the formation and age of the earth. The notion of a 6.000 year old earth was already dismissed by scholars and even the interpretation of gravel and sand deposits as the remains of the biblical flood (the “Diluvium“) was questioned. However the notion of earth’s history of a succession of catastrophic events was still fiercely discussed.

Many geologists at the time proposed that geologic processes in the past differed significantly from recent processes; even certain types of rocks (and the formation of these rocks) were limited to certain time periods, when today unknown geological processes were shaping the earth. The lawyer Charles Lyell challenged this interpretation of earth’s history, arguing that common and slow processes still observable today also acted long time ago.

Captain FitzRoy offered Charles Lyell’s recently published and controversial “Principles of Geology” as welcoming gift, but Darwin probably didn’t find time to read the book in the first weeks of the expedition. His former mentor, botanist John S. Henslow, even “advised me to get and study the first volume of Principles, which had then just been published, but on no account to accept the views therein advocated.“

It’s therefore even more surprising to read in Darwin’s autobiography (1876-1881) the following phrase:

“The very first place which I examined, namely St. Jago, in the Cape de Verde islands, showed me clearly the wonderful superiority of Lyell’s manner of treating geology.”

Darwin also emphasises how the visit of St.Jago converted him to Lyell’s geology:

“The geology of St. Jago is very striking, yet simple: a stream of lava formerly flowed over the bed of the sea, formed of triturated recent shells and corals, which it has baked into a hard white rock. Since then the whole island has been upheaved. But the line of white rock revealed to me a new and important fact, namely that there had been afterwards subsidence around the craters, which had since been in action, and had poured forth lava. It then first dawned on me that I might perhaps write a book on the geology of the various countries visited, and this made me thrill with delight. That was a memorable hour to me, and how distinctly I can call to mind the low cliff of lava beneath which I rested, with the sun glaring hot, a few strange desert plants growing near, and with living corals in the tidal pools at my feet.“

Fig.1. Profile of the island of St. Jago as seen by Darwin in 1832. Darwin was the first to study the geology of the Cape Verde Islands (from DARWIN 1876). Darwin recognized three distinct layers of rocks, a lower series with volcanic rocks composed of volcanic breccias and magma dikes (deposited under water - identified with "A"), a limestone with fossils ("B") and finally a cover of basaltic lava ("C"). Darwin, trained by Sedgwick, noted also the contact metamorphism between the former hot molten lava and the earlier cool limestone.
It is curious to note that Darwin adopted the geological terms used by German (not British) geologists to describe the rocks observed in the field, here the strong influence of Alexander von Humboldt works, read by the young Charles, is recognizable

Darwin uses in later publications the similarity of the fossils found in the carbonate sediments (Darwin’s line of white rock) and the still living animals on the shore as evidence that no substantial change in the geologic processes forming these rocks occurred over time.  
However from the geological notes he made during the field trip on St. Jago it emerges that young geologist Darwin was still struggling to accept this idea. More important, accepting slow geological processes made it necessary also to accept a very old earth.

During one of his daily excursions on St.Jago Darwin discovered a mature baobab-tree (gen. Adansonia) growing on the bottom of one of the large valleys carved into the hard basaltic rocks of the volcanic island.

“In this [one of the valleys north of Praya] grows the celebrated Baobab or Adansonia; this tree only 45 feet high, measured two feet from the ground round the solid trunk. 35.-Some of the same species in Africa were supposed by Adanson to reach the enormous age of 6000 years.-The very appearance of the tree strikes the beholder that it has lived during a large fraction of the time that this world has existed.“

Darwin notes that a 6.000 year old tree would have experienced a significant period of earth’s history, implying that earth, despite older than proposed by scrupulous clergymen, would be not much older. However the eroded valleys in the thick lava shields, characterizing the landscape on St. Jago, need vast periods of time to form, as he continues:

“Of course the valley must be older & it is this one that has finally left the neighbourhood of Praya in the state we now find it.-How long a time intervened between this period and the deposition of former beach it is impossible to say.-during it three great phenomena occurred, the flowing of the lava.-the upheaving of the coast. & the great beds of diluvium collected in the older valley.-To what a remote age does this in all probability call us back & yet we find the shells [in the 'former beach'] themselves & their habits the same as exist in the present sea.“

In the final note Darwin considers the possibility that the similarity between the fossil shells and the recent ones could also be explained by a short interval of time between the formation of the white rock and the deposition of modern beach deposits (so there was no time for a faunal turnover).
However accepting a young age for the fossil beach deposits and the even younger eroded remains of the volcanic island of St. Jago (the coastal lava shields are covering Darwin´s white rocks and therefore according to stratigraphic principles are younger) would invoke some unknown – and presumably catastrophic – geological event in the not-too distant past to explain its actual deep incised valleys.

“I conceive it to be clear, from the pieces left standing and from the corresponding appearance on each side of the valley, that the country was originally covered with a uniform bed of this rock.-and that after being shattered by some great force: these valleys were formed by the agency of large bodies of water: To this latter force the valleys nearer the coast give abundant evidence.“

Darwin will admit in his diary “what a confusion for geologists.“

To be continued…

Bibliography:

CHIESURA, G. (2010): A Santiago sulle orme di Darwin. Darwin – Bimestrale di Scienze No.40: 32-36
CHIESURA, G. (2013): Isole di Darwin – Un curioso in mezzo al mare. CD-Rom
HERBERT, S. (2005): Charles Darwin, Geologist. Cornell University Press: 485
JOHNSON, M.E.; BAARLI, B.G.; CACHAO, M.; da SILVA, C.M.; LEDESMA-VAZQUEZ, J.; MAYORAL, E.J.; RAMALHO, R.S. & SANTOS, A. (2012): Rhodoliths, uniformitarianism, and Darwin: Pleistocene and Recent carbonate deposits in the Cape Verde and Canary archipelagos. Palaeogeography, Palaeoclimatology, Palaeoecology Vol.329-330: 83-100
PEARSON, P.N. & NICHOLAS, C.J. (2007) : ‘Marks of extreme violence’: Charles Darwin’s geological observations at St Jago (Sao Tiago), Cape Verde islands. in WYSE JACKSON, P. N. (ed.) Four Centuries of Geological Travel: The Search for Knowledge on Foot, Bicycle, Sledge and Camel. Geological Society, London, Special Publications, 287: 239-253

From Nukes to Ship Disasters - how Forensic Seismology helps to understand Catastrophes

On July 25, 1946 the United States detonated the first underwater nuclear weapon in history – code name “Baker” – at the Bikini Atoll. The explosion generated a gas bubble that pushed against the water, generating a supersonic shock wave which crushed the hulls of nearby target ships as it spread out. Seismic waves of this test were observed at seismograph stations around the globe and it was realized that these waves could be used to detect and potentially characterize a nuclear explosion.

Fig.1. Photography of the underwater “Baker” nuclear explosion of July 25, 1946 showing the white sphere of water and vapour formed by the shock wave of the explosion (image in public domain).

The U.S. performed also the first fully underground explosion – code name “Ranier” – that was detected by about 50 seismic stations; however, it was confused in part with a “normal” earthquake.
 

With the ban of nuclear weapon (well, sort of…) testing in the year 1958 it became necessary to install an effective worldwide monitoring system. Three years later the set-up of the WorldWide Standardized Seismographic Network (WWSSN) began and in 1966 almost 112 stations were working in the monitoring project “Vela“. Vela provided a large quantity of supplementary seismic data used to answer three questions: Where is the seismic event located? What is the source type (artificial or natural) of the event? How large is the event?

“It appears increasingly doubtful that an atomic-weapons test of significant dimension can be concealed either underground or in outer space. A five-kiloton nuclear explosion in an underground salt cavern near Carlsbad, N.M., in December was clearly recorded by seismographs as far away as Tokyo, New York, Uppsala in Sweden and Sodankyla in Finland. The seismograph records included tracings of the ‘first motion,’ considered critical in distinguishing between earthquakes and underground explosions.” from “Scientific American“, February 1962

The signature of a natural earthquake shows a distinct pattern: a seismometer will first detect the Primary and Secondary Waves, followed by the more destructive Surface or Rayleigh Waves.
Seismic P Waves are compressional waves, similar to sound waves in the air. Secondary or Shear (S) Waves are transverse waves, like those that propagate along a rope. A sudden explosion generates a “sphere” of compressional waves travelling in all directions. In contrast an earthquake is caused by the sliding of rocks along a fracture and it will generate shear waves concentrated in a certain direction. Therefore an explosion will show a strong and sudden signal of P-waves, with a similar signal recorded by all the seismometers collocated around the explosion. An earthquake will show a more complex pattern, depending of the position of the seismometer, characterized by strong S-Waves and R-Waves.
Also an underground explosion does not generate very strong surface waves as a natural earthquake does.

Fig.2. Schematic seismogram with Primary (P; compressional waves), Secondary (S; shear waves), and Rayleigh (R; surface waves) phases for an artificial blast and a natural earthquake.

As every atomic explosion will generate a unique pattern, distinct from natural earthquakes, seismology is a reliable tool to control the ban of nuclear test and to supervise countries that still test atomic weapons.

The information recovered from seismograms of nuclear blasts can be applied in forensic seismology also to study detonations of common explosives. Most spectacular cases in the last years comprise the reconstruction of the Oklahoma City bombing in 1995 (see this abstract by HOLZER at the AGU meeting in 2002) and the investigation in the explosion on the Russian submarine “Kursk” in 2000 (see KOPER et al. 2001; the blog “About.com Geology” hosts many other examples).

Seismic waves can be generated not only by shear movements along faults or by the expansion of plasma (nuclear device) or gas (conventional device) during an explosion, but also by the impact of objects with the ground.
Seismic signals were already used to identify the location of rock-falls and recent research suggests that the signals can help to characterize the dynamics and volume of a landslide, Dave Petley discusses the significance and use of seismograms in various posts published on his “Landslide blog“.

The analysis of seismic waves provided also insights on what happened September 11, 2001 in New York. Seismograph stations around the city recorded the signals generated by the aircraft impacts and the subsequent collapse of the two towers of the World Trade Center (the Lamont-Doherty Cooperative Seismographic Network provides a rich collection of datasets of the seismic activity around N.Y.). The collapse of the south tower generated a signal with a magnitude of 2.1 and the collapse of the north tower, whit a signal of magnitude 2.3, was recorded by 13 stations ranging in distance from 34 to 428 km.
Also these seismograms show a distinct pattern if compared to the pattern caused by a natural earthquake. There are no P or S Waves, but the impacts of the buildings on the ground generated a sudden peak of short-period Rayleigh Waves.

Fig.3. Seismic recordings at the seismograph station Palisades (N.Y.) for events at World Trade Center on September 11, distance of station from Ground Zero ~ 34 km. Note that impact 1 and collapse 2 relate to the north tower, and impact 2 and collapse 1 apply to the south tower. Expanded views of the first impact and first collapse shown in red. Figure from KIM et al. 2001, published here according to the Usage Permissions granted by AGU & authors.

The seismograms show also that the impact and explosion of the two airplanes generated a relative small amount of seismic energy. This confirms the observation that the collapses of the two towers were not a direct result of the impacts, but caused by the weakening of the supporting structures of the buildings due the subsequent fires.

Most energy of the collapses was dispersed into the deformation of the buildings and the formation of rubble and dust, only a small portion of potential energy was converted into seismic waves. The generated 2.1 and 2.3 M earthquakes were too weak to destabilize nearby buildings, most damage was done by the kinetic energy of the debris and the displaced air.

Also the collision of the cruise ship “Costa Concordia” on January 13, 2012 was recorded by the seismograph station “Monte Argentario“, situated on the Italian mainland. From the eyewitness testimony and the Automatic System of the ship the time of collision with a submerged rock was estimated at 20:45 (UTC). This time is confirmed by a sudden peak in the seismogram at 20:45:10 (the seismograph station is distant 18 km from the site of the collision, the seismic waves needed almost 3-4 seconds to travel this distance). The seismogram shows also after the impact the “noise” generated by the hull of the ship grinding along the rocky substrate.

Fig.4. Seismogram recorded at the station “Monte Argentario” (Italy) showing the seismic waves generated by the impact of the “Costa Concordia” on January 13, 2012 20:45 (UTC). An accurate analysis of “The seismic wake of “Costa Concordia” (23.01.2012) can even specify the speed of the ship at the moment of the collision. Figure used with permission and taken from the post “The earthquake of the Costa Concordia” by Italian seismologist Marco Mucciarelli, published January 21, 2012 on his blog “terremoti, sismologia ed altre sciocchezze“.

Bibliography:

ANDERSON, D.N.; RANDALL, G.E.; WHITAKER, R.W.; ARROWSMITH, S.J.; ARROWSMITH, M.D.; FAGAN, D.K.; TAYLOR, S.R.; SELBY, N.D.; SCHULT, F.R.; KRAFT, G.D. & WALTER, W.R. (2010): Seismic event identification. WIREs Computational Statistics Vol.2, July/August: 414-432
KIM, W.-Y.; SYKES, L.R.; ARMITAGE, J.H.; XIE, J.K.; JACOB, K.H.; RICHARDS, P.G.; WEST, M.; WALDHAUSER, F.; ARMBRUSTER, J.; SEEBER, L.; DU, W.X. & LERNER-LAM, A. (2001): Seismic Waves Generated by Aircraft Impacts and Building Collapses at World Trade Center, New York City. EOS Vol.82 (47)

KOPER, K.D.; WALLACE, T.C.; TAYOLR, S.R. & HARTSE, H.E. (2001): Forensic seismology and the sinking of the Kursk. EOS, Vol.82 (4): 37

January 11, 1771: The Birthday of Lake Alleghe

The lake of Alleghe in the valley of Cordévole is today exactly 244 years old. The "birthday" of this lake is well known, at 7:02 in the morning of January 11, 1771 the river flowing through the valley became dammed by a landslide coming from the mountain Piz.

Fig.1. General view of the valley of Cordévole with the village and lake of Alleghe. On the right, on the mountain Piz, the scar of the landslide is barely visible in the forest, in the background the Civetta (3.220m).

The Alps-traveler Belsazar Hacquet (1739-1815) remembers a visit to the lake in 1780:

“The river Cordévole became my guide, by following him I would find the valley of Cadore. But only after some hundred steps the river was flowing in a large lake, existing here only for the last nine years. I walked around in eastern direction, to the villages of Sternade and Saviner until the mountain of Piz. First the lake was narrow, only by Saviner it became more than 100 venetian fathom [an old length unit used in the mining industry of these times, one fathom ca.1,8m] broad and more than thirty deep. The last mentioned village once was situated on a hill, before it in a broad valley there were four smaller villages…[]…which became flooded by the lake, but the fourth locality, named Marin, was buried with the village of Riete under the collapse of the mountain of Piz, last mentioned village situated previously on the top of the mountain.” Standing on the top of the mountain, I immediately noted that the mountain has a volcano on top of it, and it was possible to see how deep it went. After the mountain collapsed, it could be seen that its base was composed of limestone, build up by mighty layers, dipping from the west to the east with 45 degrees. The surface of the collapse is so smooth, that a man has difficulties to climb on it to the mountain.“

 

Fig.2. Historic depiction of the landslide-lake in the “Atlas Tyrolensis” of 1774 by Tyrolean cartographers Peter Anich and Blasius Hueber. Note the landslide-boulders on the southern shore of the lake, Anich and Hueber were one of the first cartographers to use signatures to display geomorphologic features in their maps (image in public domain).

The strange notion by Hacquet of an active volcano in the Dolomites in very recent times is based maybe on his discovery of volcanic rocks in the area, however – as we today know – these deposits are more than 235 million years old. At the time of Hacquet’s geologic investigation volcanic forces were also believed to cause strong and sudden movements of the terrestrial surface, effects that maybe could also explain a sudden disaster, like a landslide. Also notable how Hacquet describes the surface where the landslide “slipped away”.

Fig.3. Detail of the modern geological map (Carta Geologica delle Tre Venezie, Foglio 12 "Pieve di Cadore", 1940) showing the village and the landslide of Alleghe (with the lake in the lower part of the map) and the dammed lake.

The detachment area of the landslide is composed by Anisian dolostone (Contrin-fm) overlying limestone - layers and marls of the Ladinian (St. Kassian-fm).

 Lithology: pink = Anisian dolostone (Contrin-fm), blue= Anisian dolostone, lower succession (Moena-fm), brown= marls with bedded limestone-layers (St. Kassian-Formation).

Detail of the geological map (Carta Geologica delle Tre Venezie, Foglio 12 "Pieve di Cadore", 1940) showing the village and the landslide of Alleghe (with the lake in the lower part of the map) and the dammed lake, lithology: pink = Anisian dolostone (Contrin-fm), blue= Anisian dolostone, lower succession (Moena-fm), brown= marls with bedded limestone-layers (St. Kassian-Formation). - See more at: http://historyofgeology.fieldofscience.com/2011/01/11-january-1771-landslide-of-alleghe.html#sthash.3iyCIGcp.dpuf

The landslide of Alleghe killed 48 people and destroyed parts of the village of Riete and some farms. The landslide-lake inundated the village of Peron, only in February 1771 a new outflow formed and stabilized the lake level.

Bibliography:

HÖFLER, H. & WITT, G. (2010): Katastrophen am Berg – Tragödien der Alpingeschichte. Bruckmann Verlag: 144

January 6, 1912: Happy Birthday Continental Drift!

January 6, 1912 the German meteorologist Alfred Wegener presented in a lecture entitled “Die Heraushebung der Großformen der Erdrinde (Kontinente und Ozeane) auf geophysikalischer Grundlage” (The uprising of large features of earth’s crust (Continents and Oceans) on geophysical basis) for the first time his hypothesis of the ancient supercontinent Pangaea, from which all modern continents split apart.
Three years later he will publish his book “Entstehung der Kontinente und Ozeane“, translated in the third edition and published in 1922 as “The origin of continents and oceans.”
 

Wegener didn’t propose something completely new; as he based his idea on earlier observations and suggestions, but his work started a fierce discussion in the scientific community.

  

In 1889 and 1909 the Italian musician and naturalist Roberto Mantovani published a hypothesis based on his observations on the volcanic island of Réunion: cracks forming during volcanic eruptions could separate even large parts of an island, could it then be possible that entire continents split apart? Mantovani collected various evidence and published maps to show the shape of the hypothetical former continents (Wegener will use these maps to support his idea), however he explained the driving force behind the breakup of former large continents by the slow expansion of the earth.
 

In 1908 the self-educated geologist Frank B. Taylor proposed that the crust of earth was influenced by tidal forces of the moon and the continents were pulled apart in some regions and pushed together in other areas, forming folds like a carpet. However the involved forces were to weak and his explanation wasn’t deemed plausible. The Austrian geologist Otto Ampferer speculated in 1906 that the Alps were formed by folding of the upper crust, as driving force he proposed magma sinking into the mantle and pulling pieces of crust downwards (!). This “Unterströmungstheorie (also Subfluenztheorie)” lacked however a convincing source of energy and couldn’t explain all aspects of the genesis of the Alps, as it implied only pulling and not compressive forces needed to form folds and faults.

Wegener became interested in the idea of a single continent in 1910 by observing an atlas and noting the coasts of the Africa and South American. Some time later he read a paleontological paper discussing the similarities of terrestrial fossils between separated continents.
 
Wegener continued to collect various published evidence to support his theory of a single continent:
- Like a puzzle also the outlines of continents (especially the continental shelves) seem to fit together.
- There are various geomorphologic and geological similarities along the coasts of South America-Africa and Europe-North America.
- Fossil of land vertebrates and plants can be found on different continents, separated today by large oceans.
- Fossil evidence of ancient climates, today without a recognizable pattern, will form climate zones when the continents are put together.

Wegner considered the prevailing explanation for the patterns in the fossil record as impossible: ancient land bridges that connected continents and habitats (like the Isthmus of Panama today) were composed of light continental granitic crust, such pieces of less dense rocks couldn’t simply sink into the much denser oceanic basalts and disappear without trace.

He will explain in 1911 his idea in a letter to his father-in-law, Professor Wladimir Peter Köppen:

“You consider my primordial continent to be a figment of my imagination, but it is only a question of the interpretation of observations. I came to the idea on the grounds of the matching coastlines, but the proof must come from the geological observations.
These compel us to infer, for example, a land connection between South America and Africa. This can be explained in two ways: the sinking of a connecting continent or separation. Previously, because of the unproven concept of permanence, people have considered only the former and have ignored the latter possibility. But the modern teaching of isostasy and more generally our current geophysical ideas oppose the sinking of a continent because it is lighter than the material on which it rests. Thus we are forced to consider the alternative interpretation. And if we now find many surprising simplifications and can begin at last to make real sense of an entire mass of geological data, why should we delay in throwing the old concept overboard?“

 

  

Wegener hypothesis of continental drift (a catchy phrase adopted mainly by the critics, as Wegener talks more general of “displacement theory“) was received with mixed feelings. Most geologists regarded it as cherry-picking of anecdotes from the literature. However some geologist with field experience, especially in Africa and South-America, became soon convinced of this possibility.

Like Taylor also Wegener could not explain the forces necessary to move the continents in the crust. Wegener imagined that continents - like gigantic ice floes - swim on and are surrounded by the much denser oceanic crust.  He proposed gravitational pull, tidal and centrifugal forces, but the English geophysicist Harold Jeffreys demonstrated that these forces are much too weak or if strong enough, had to stop first earth’s rotation.
 
Wegner himself reacted to the critics and tried to respond to them in various editions of his books, however with moderate success. The greatest problem remained the lack of direct evidence for the movements of continents and the needed explanation for the mechanism and also the large amount of energy needed to move and deform rocks. Most importantly Wegener considered his work as starting point and stimulus for other or even future scientists, a message that wasn’t fully understand at his time.

 

Fig.1. – 3. “Eppur si muove!” Reconstruction of the former supercontinent of Pangaea and the subsequent breakup in various smaller continents from the Carboniferous to the Quaternary. From WEGENER, A. (1929): Die Entstehung der Kontinente und Ozeane. 4th ed.

Wegener will die in 1930. His continental drift hypothesis is in many aspects erroneous: not the single continents move but entire plates of the crust and the driving force comes from within the planet, not from outside. However his most important legacy is to have introduced the idea of moving continents to the scientific community and the public (even Lovecraft will became inspired by Wegener’s writings) – decades later this legacy will influence a new kind of theory: Plate Tectonics.

Bibliography:

MILLER, R. & ATWATER, T. (1983): Continents in Collision. Time-life books, Amsterdam: 176
SCALERA, G. (2003): Roberto Mantovani an Italian defender of the continental drift and planetary expansion. From Scalera, G. and Jacob, K.-H. (eds.): Why expanding Earth? – A book in honour of O.C. Hilgenberg. INGV, Rome: 71-74