oleh Ken Wohletz Los Alamos National Laboratory LA-UR 00-4.608 Copyright © 2000 UC
Sejarah modern memiliki kaitan asal-usul ke abad 6-7. Selama periode ini terjadi kegagalan pertanian dan munculnya wabah yang mempunyai andil dalam:
(1) keruntuhan kota Super kuno, Persia kuno, peradaban Indonesia, budaya Nasca dari Amerika Selatan, dan peradaban Arab selatan,
(2) perpecahan kekaisaran Roma dengan konsepsi negara bangsa banyak dan kelahiran kembali dari Cina bersatu, dan
(3) asal-usul dan penyebaran Islam, sementara Kristen Arian menghilang.
Dalam bukunya yang bejudul ” Bencana, Sebuah Investigasi ke dalam Asal Usul Dunia Modern”, penulis David Keys mengeksplorasi sejarah dan arkeologi untuk menghubungkan semua gejolak manusia terkait destabilisasi iklim yang disebabkan oleh bencana alam, dengan bukti yang kuat dari Data lingkaran pohon dan inti es yang terjadi pada tahun 535 M.
Deskripsi bahwa ada masa-masa dengan cahaya matahari yang berkurang, dingin terus-menerus, dan anomali salju di saat musim panas tercatat dalam laporan tertulis abad ke 6 Masehi. Tulisan-tulisan dari China dan Indonesia menggambarkan fenomena atmosfer langka yang mungkin menunjuk ke sebuah gunung berapi di jalur sabuk api Indonesia.
Meskipun jejak radiokarbon letusan di bagian dunia tidak teridentifikasi, ada bukti kuat batimetri dan vulkanik, bahwa Krakatau mungkin pernah mengalami letusan kaldera besar. Oleh karena itu, studi ini mendorong ekspedisi ilmiah yang akan dipimpin oleh Haraldur Sigurdsson ke daerah tersebut.
Ekspedisi menemukan deposit piroklastik tebal, dengan penanggalan (dating) radiometrik yang tepat, yang merekomendasikan adanya peristiwa runtuhnya kaldera dari “Proto-Krakatau” memang terjadi mungkin pada abad ke 6.
Batimetri menunjukkan diameter kaldera 40 s.d. 60 km, dengan runtuhnya di bawah permukaan laut, dapat terbentuk Selat Sunda, memisahkan Jawa dari Sumatra, seperti yang dicatat oleh tulisan-tulisan sejarah kuno Jawa. Seperti runtuhnya kaldera akibat letusan beberapa ratus kilometer kubik puing-puing awan panas, yang beberapa kali lebih besar dari letusan tahun 1815 dari Gunung Tambora.
kemungkinan hipotetis Letusan ini ADALAH interaksi magma dan air laut , seperti yang diceritakan dalam dokumen letusan Krakatau masa lalu , tetapi pada skala yang luar biasa. Simulasi komputer dari letusan menunjukkan bahwa interaksi ini bisa menghasilkan plume dari 25 km sampai > 50 km tinggi, membawa dari 50 sampai 100 km kubik air laut menguap ke atmosfer.
Meskipun sebagian besar uap mengembun dan jatuh dari ketinggian rendah, sejumlah besar yang masih lofted ke stratosfer, membentuk awan es bercampur material super halus (Wohletz KH, 2000).
Apakah Abad Kegelapan dipicu oleh gunung berapi yang berhubungan dengan perubahan iklim pada abad ke-6? EOS Trans Amer Geophys Union 48 (81), F1305. ( Presentasi Kendali dalam format PDF )
Meskipun dampak asteroid/komet tetap sebagai penyebab potensial, kita fokus pada sumber vulkanik yang terletak di dekat katulistiwa. Lebih dari 100 gunung berapi di khatulistiwa potensial untuk dipertimbangkan, kita menemukan bukti terbaik menguatkan di Indonesia, di mana terputusnyas geo-politik sekitar abad ke-6 didokumentasikan dengan baik.
Uji Carbondating umur Tephra sangat berguna, tapi perlu hati-hati. Sebagai contoh, beberapa tanggal diterbitkan oleh Rabaul yang tampaknya seperti cocok ternyata keliru. Itu adalah terjemahan dari “Pustaka Raja Purwa” (Kitab Raja-raja kuno) di Jawa yang memperingatkan Keys David dan kita untuk letusan besar Krakatau pada tahun 338 dari Kalender Shaka, yang dikenal kemungkinan besar akan sejajar dengan tanggal kalender Barat AD 416. Kita menghabiskan banyak waktu mengidentifikasi dan menerjemahkan teks yang dapat dibuktikan yang tidak “terkontaminasi” sebanyak 1.883 tulisan, dalam teks itu adalah pemisahan Jawa dari Sumatera pada tradisi Jawa kuno tentang bencana yang sesuai deskripsi besar ledakan letusan.
Dengan kata lain, runtuhnya kaldera yang menghasilkan Selat Sunda modern. Studi Krakatau pra letusan tahun 1883 dari grafik Admiralty Inggris Selat Sunda menunjukkan kedalaman dasar laut dangkal (~ 10 m) di selat, dan pulau-pulau Krakatau, Sebesi, Sebuku, Sertung, dan pegunungan dekat Katimbang (Matius Rajah Bassa), pulau-pulau ini dapat menjadi sisa-sisa ventilasi vulkanik yang mengelilingi sisi-sisi Proto-Krakatau, pendahulu dari gunung berapi Krakatau.
Menghubungkan ventilasi ini menguraikan kaldera dengan diameter permukaan ~ 50 km berpusat di Selat Sunda sekitar 20 km Timur Laut dari Krakatau saat ini. Menggambar bagian barat-ke-timur silang dari runtuhnya kaldera hipotetis, menunjukkan bagaimana Selat Sunda mungkin telah terbentuk selama letusan abad ke-6 dari Proto Krakatau.
Untuk menguji hipotesis ini kaldera Proto-Krakatau, melalui saluran Inggris 4 melakukan penggalangan dana untuk mendanai sebuah ekspedisi pada tahun 1999 untuk meneliti Selat Sunda.
Aku meminta kepada Haraldur Sigurdsson dan Steven Carey untuk melakukan upaya ini karena keakraban mereka dengan wilayah tersebut. Mereka berhasil menemukan deposit batu apung dan abu dari letusan eksplosif besar yang penanggalan karbon dating-nya antara 6600 SM dan 1.215 Masehi. Tentu saja tidak konklusif, namun indikasi kesulitan dalam mengenali bukti letusan ledakan tua di lingkungan tropis dan / atau kapal selam.
Seri berikutnya adalah gambar dari simulasi komputer tentang peristiwa letusan. Letusan pertama adalah dari jenis yang dikenal sebagai “freatik,” yang melibatkan magma yang tidak baru, melainkan debu dan batu ditiup keluar dari kawah Proto Krakatau menjadi semburan uap, yang dibentuk seperti merebus air tanah di bawah gunung berapi oleh panas magma saat mendekati permukaan Awal letusan yang benar-benar raksasa ditandai dengan penampilan kaku, kental, 900 derajat C magma di permukaan yang begitu tinggi, gas itu meledak keluar dari gunung berapi dengan kekuatan ratusan bom nuklir. Ledakan ini, yang dikenal sebagai letusan “Ultra Plinian” (setelah Pliny tua yang menyaksikan jauh lebih kecil tetapi serupa dalam fenomena penampilan selama letusan Vesuvius AD79), batu apung, abu, dan gas sebagai jet keluar dari gunung berapi, ledakan jet meningkat menjadi sekitar 50 km ke stratosfer. Kecepatan naik gas, batu apung, dan abu cenderung melebihi kecepatan suara, dan mendorong gelombang kejut dengan kecepatan hampir dua kali lipat dari suara (~ 650 m / s ). Melontarkan batu apung dan abu ke atmosfir dengan kekuatan 100-1.000.000.000 kg per detik, banyak yang jatuh setelah mencapai ketinggian tertentu di langit menjadi selimut setebal beberapa meter diatas tanah sekitarnya, terdiri dari batu apung dan abu (lapisan biru muda pada ilustrasi di bawah).
Lontaran batu apung, abu, dan gas panas tinggi ke stratosfer, melayang di stratosfir terbawa angin mengelilingi bumi dari barat ke timur. Sebagai letusan Plinian Ultra terus tanah di bawah gunung berapi mulai mereda, secara bertahap jatuh ke bagian beberapa km dievakuasi dari dapur magma di bawah. Dengan penurunan ini, runtuhnya dinding terbuka di sekitar gunung berapi, yang memungkinkan air laut untuk mengisi ke dalam saluran magma yang menghubungkan dapur magma dan gunung berapi.
Air laut ini menguap seketika dengan kekuatan ledakan tambahan, sehingga letusan yang disebut “Phreatoplinian,” yang berkonotasi kombinasi letusan Plinian dengan freatik (dekat permukaan) air. Penambahan sejumlah besar uap air ke kolom letusan menyebabkannya runtuh dengan sendirinya, tumpah keluar awan abu, batu apung, dan uap yang meluncur di lereng sekitarnya dengan kecepatan hingga ratusan meter per detik, melambat untuk puluhan meter per detik setelah perjalanan sekitar 10 km dari gunung berapi, namun terus menerjang apa saja yang ada di lereng hingga 50 km atau lebih dari gunung berapi.
“aliran piroklastik” ini benar-benar menghapuskan semua vegetasi dan setiap struktur hunian. Menganalisis Letusan tersebut Sedangkan simulasi erupsi sebelumnya memberikan gambaran kualitatif yang baik tentang bagaimana letusan berkembang, kita menginginkan informasi yang lebih rinci, khususnya mengenai parameter fisik letusan. Beberapa parameter tersebut dapat dibatasi dengan mempertimbangkan skala letusan digambarkan di atas, sementara yang lain harus dihitung. Dengan menggunakan hasil simulasi superkomputer yang memecahkan persamaan matematika yang mengekspresikan perilaku fisik letusan, kami mendapatkan hasil yang berguna untuk model gelombang atmosfer dan suara.
Durasi Letusan: Dari ukuran kaldera diasumsikan, kami menunjukkan di atas bahwa ~ 200 km 3 dari magma itu meletus. Untuk letusan sebesar ini, skala letusan sejarah yang lebih kecil menunjukkan tingkat debit massa 1 miliar kg per detik atau lebih. Fluks ini setara dengan satu-satu seperseribu 3 km per detik atau 3,6 km 3 per jam. Semua parameter lainnya sama, letusan akan diambil setidaknya 34 jam, tetapi karena waxing dan waning fluks selama letusan, bagian cataclysmal dari letusan mungkin telah berlangsung selama 10 hari. Bahkan, letusan tersebut mungkin terjadi di hari-panjang pulsa, yang terjadi selama bertahun-tahun.
Produk Letusan: Sebagian besar magma sudah terpecah-pecah oleh kekuatan luar biasa dari letusan menjadi potongan-potongan batu apung dan abu.Terutama selama letusan Phreatoplinian, abu adalah bentuk yang diinginkan diusir.dari magma Abu ini terdiri dari fragmen kecil dari pecahan batu dan kaca, dengan diameter mulai dari r sekitar 1 mikrometer sampai beberapa milimeter . Selama letusan Phreatoplinian, sebanyak 50% dari abu ini bisa saja terdiri dari fragmen berdiameter kurang dari 50 mikrometer . Fragmen kecil tersebut telah sangat lama menghuni di atmosfer tinggi, dapat disimpan tinggi- selama berbulan-bulan oleh turbulensi atmosfer normal. Dengan asumsi bahwa 75% dari total 125 km3 dari magma yang terlibat dengan letusan Phreatoplinian, mungkin sebanyak 30 km3 dari partikel abu halus dimasukkan ke dalam sirkulasi global.
Belerang dari magma kemungkinan kental pada partikel abu tetesan asam sulfat, namun kelimpahannya tidak diketahui.
Kelembaban udara: Seiring dengan, batu apung dan abu banyak air menguap dan disuntikkan ke dalam atmosfer dan stratosfer, terutama selama fase Phreatoplinian dari letusan, mungkin volumetrically yang paling penting dari fase cataclysmal. Untuk penguapan air yang optimal, magma cair mengandung cukup panas untuk menguapkan volume kira-kira sama air.
Dengan asumsi bahwa 75 dari 125 km total 3 dari magma berinteraksi dengan air, 75 km 3 yang menguap, yang setelah ekspansi ke tekanan atmosfer mungkin telah menduduki hampir 100.000 km 3 dari atmosfer. Yang pasti, banyak dari uap ini akan terkondensasi yang jatuh sebagai abu-tersumbat hujan dengan di jam letusan, tapi mungkin sebanyak setengah dari itu dilakukan di seluruh dunia oleh angin stratosfer. Uap ini akan terkondensasi sampai membentuk kristal es, dan ini kristal es ini akan menyebar di udara untuk membentuk awan rarified stratus, gelap oleh abu entrained. Seiring dengan uap air dari klorin laut yang juga dibawa ke stratosfer, komponen yang berpengaruh penting pada kimia stratosfir.
Struktur Jet dan Plume :
Jet abu, batu apung, dan gas muncul dari terowongan ventilasi pada kecepatan supersonik dari 650 m/s, tetapi melambat sampai memperlambat kecepatan kenaikan apung beberapa puluh meter per detik setelah mencapai 10 sampai 15 km ke atmosfer. Membanggakan apung memiliki energi yang cukup untuk terus meningkat menjadi hampir 50 km sebelum menjadi netral apung dan mulai menyebar lateral. Lebar jet dan membanggakan selama fase erupsi Plinian mungkin berkisar dari beberapa km pada dasarnya banyak sebanyak 40 km di dekat puncaknya, tepat di bawah tingkat di mana ia menyebar sebagai awan landasan berbentuk raksasa.
Konsentras iAsh dalam bulu-bulu menurun ke atas karena campuran udara ambien ke bulu-bulu seperti naik, tetapi konsentrasi mungkin tinggal di tingkat 1 bagian dalam satu juta volume.
Ini adalah perkiraan yang sangat konservatif volume membanggakan total selama letusan, memberikan nilai lebih dari 100 juta km3 dan kemungkinan mencapai beberapa kali lipat lebih besar.
Ringkasan:
Besarnya Keruntuhan 100 m lebih dari 50-km kaldera berdiameter dapat melibatkan letusan ~ 200 km3 magma Scaling serupa berukuran letusan memprediksi fluks massa ~ 10^9 kg/s Lamanya Letusan dari 200 km3 dari magma pada 10^9 kg/s membutuhkan setidaknya ~ 60 jam letusan terus menerus Letusan terus menerus tidak mungkin, sehingga durasi mungkin telah berlangsung dari minggu ke lebih dari satu bulan Tephra Dominan batu apung dan abu Untuk letusan phreatoplinian hingga 50% berat-dari tephra dapat terfragmentasi menjadi abu halus (mm) Jika 75% dari vol-produk yang meletus adalah phreatoplinian, 75 km3 dari abu halus yang disuntikkan ke atmosfir Gas Dominan H 2 O Untuk kuat air / magma interaksi, volume air menguap hampir sama dengan volume magma dalam interaksi Jika 75% vol-dari produk meletus mengalami kuat air / magma interaksi kemudian 150 km3 dari air laut yang menguap, menciptakan hingga 200.000 km3 dari uap air di atmosfer Kemungkinan sebagian besar (50% vol-atau lebih) terkondensasi suatu endapan dari ketinggian rendah Sisa uap kristal es mungkin terbentuk di stratosfer Plume Struktur Meletus dengan kecepatan hingga 650 m/s, kolom letusan mungkin telah melampaui 50 km di ketinggian sebelum mencapai daya apung netral Dari model numerik, konsentrasi Volume tephra setelah pencampuran dengan atmosfer adalah 10 -6 atau kurang Jika komponen baik-abu tetap di bulu-bulu dengan uap air yang terbentuk kristal es, maka volume total dapat membanggakan telah mencapai beberapa puluh juta km3
Atmosfer Wonderings
Pertimbangkan volume besar bulu-bulu abu dan uap (10-80000000 km3).
Luas Tropopause permukaan bumi adalah ~ 5.2×10 8 km2. Letusan membanggakan bisa menghasilkan lapisan awan 20-150 m tebal atas seluruh dunia. Dengan sumber membanggakan dekat khatulistiwa, kedua belahan otak utara dan selatan akan terpengaruh. Seperti segumpal vulkanik berkekuatan besar belum pernah dipertimbangkan untuk CGMS, dan analog yang hanya mungkin membanggakan ejecta dari dampak KT.
Penerapan model musim dingin nuklir (jelaga) untuk dampak KT mengindikasikan seperti beban partikel di stratosfer akan menyebabkan runtuhnya troposfer. Selain volume besar uap air dapat menghasilkan awan besar es stratosfir, menyebabkan kerusakan ozon.
Were the Dark Ages Triggered by Volcano-Related Climate Changes in the 6th Century?
(If so, was Krakatau volcano the culprit?)
Modern history has its origins in the tumultuous 6th and 7th centuries. During this period agricultural failures and the emergence of the plague contributed to: (1) the demise of ancient super cities, old Persia, Indonesian civilizations, the Nasca culture of South America, and southern Arabian civilizations; (2) the schism of the Roman Empire with the conception of many nation states and the re-birth of a united China; and (3) the origin and spread of Islam while Arian Christianity disappeared. In his book, Catastrophe An Investigation into the Origins of the Modern World, author David Keys explores history and archaeology to link all of these human upheavals to climate destabilization brought on by a natural catastrophe, with strong evidence from tree-ring and ice-core data that it occurred in 535 AD. With no supporting evidence for an impact-related event, I worked with Keys to narrow down the possibilities for a volcanic eruption that could affect both hemispheres and bring about several decades of disrupted climate patterns, most notably colder and drier weather in Europe and Asia, where descriptions of months with diminished sun light, persistent cold, and anomalous summer snow falls are recorded in 6th-century written accounts. Writings from China and Indonesia describe rare atmospheric phenomena that possibly point to a volcano in the Indonesian arc. Although radiocarbon dating of eruptions in that part of the world are spotty, there is strong bathymetric and volcanic evidence that Krakatau might have experienced a huge caldera eruption.
Wohletz KH, 2000, Were the Dark Ages triggered by volcano-related climate changes in the 6th century? EOS Trans Amer Geophys Union 48(81), F1305. (Full Presentation in PDF format)
Krakatau?
Tree-ring data from Keith Briffa (CRU, Univ. of East Anglia), corroborated by European data compiled by Mike Baillie (Queen’s Univ., Belfast), shows clear evidence of a 535 AD climate perturbation, and it is now known worldwide. The origins of this event are likely to have been volcanic since ice core from Greenland and Antarctica show sulfuric acid spikes during this time interval, and for the Byrd core (Antarctica), it is the largest in the last 2000 years. David Keys and I worked with Claus Hammer (Niels Bohr Institute) to reinvestigate the GRIP core from Greenland that Clausen et al. (1997) had already identified.Although asteroid/comet impact remain as potential causes, I focus on a volcanic source located near the equator. Of over 100 potential equatorial volcanoes considered, I found best corroborating evidence in Indonesia, where 6th Century geo-political discontinuity is well documented. Tephra dates are very useful, but there can be pitfalls. For example, some published dates for Rabaul that looked like a fit turned out to be erroneous. It was a translation of the Javenese “Pustaka Raja Purwa” (The Book of Ancient Kings) that alerted David Keys and I to a massive eruption of Krakatau during the 338th year of the Shaka Calendar, which is known to likely be misaligned to the western calendar date of AD 416. We spent considerable time identifying and translating text that could be demonstrated as not having been “contaminated” by post 1883 writings, and in that text is the ancient Javanese tradition of the separation of Java from Sumatra in a cataclysm that fits a description of a large explosive eruption. In other words, a caldera collapse that produced the modern Sunda Straits.
A pre-1883 British Admiralty chart of Sunda Straits shows shallow (~10 m) depths of sea floor in straits, and islands of Krakatau, Bezee, Sebooko, Thwart way, and mountains near Katimbang (Mt. Rajah Bassa); these islands may be vestiges of volcanic vents surrounding the flanks of Proto-Krakatau, the predecessor of the present Krakatau (Krakatoa) volcano. Connecting these vents outlines a caldera with a surface diameter of ~50 km centered in the Sunda Straits about 20 km NE of present day Krakatau.
Drawing a west-to-east cross section of hypothetical caldera collapse, shows how Sunda Straits might have formed during the 6th century eruption of Proto Krakatau.
In order to test this Proto-Krakatau caldera hypothesis, I arranged through the UK Channel 4 to fund an expedition in 1999 to the Sunda Straits. I asked Haraldur Sigurdsson and Steven Carey to undertake this effort because of their familiarity with the region. They succeeded to find a pumice and ash deposit from a large explosive eruption that carbon dating bracketed between 6600 BC and 1215 AD. Certainly not conclusive, but indicative of the difficulties in recognizing evidence of old explosive eruptions in a tropical and/or submarine environment.
Reconstructing the Eruption
If one assumes that the average amount of collapse over the entire caldera area averaged ~100 m, then the volume of collapse was approximately 200 km3. This volume is a rough estimate of the amount of magma evacuated from the magma chamber at a depth of several km below the Sunda Straits, a chamber that might have held over a 2000 km3 of magma at the time of eruption (a cylindrical body 50 km in diameter and several km thick).The 6th century eruption likely started with widespread tumescence of the ground over an area of a thousand square kilometers around Proto Krakatau, occurring over a period of years and reaching a magnitude of several meters or more near Proto Krakatau. This rising of the ground was likely to have proceeded so slowly that people in the area might not have noticed it, but they would have noticed the ever increasing occurrence of small earthquakes that perhaps were felt every few weeks in the year before the giant eruptions and reached nearly continuous shaking in the weeks before the eruption.
The following illustrations were generated by the volcanic eruption simulator, Erupt3, and they depict cross-sectional views of the Sumatra-Java island arc structure, built up by volcanism over thousands of years, consisting of layers of lava, pumice, and ash (red, magenta, and green colors). Proto-Krakatau is shown as a cone-like structure forming a land area connecting Sumatra to the west and Java to the east.
The next series of pictures are snap shots of a computer simulation of eruptive events. The first eruptions were of a type known as �Phreatic,� involving no fresh magma, but rather dust and rocks blown out of the crater of Proto Krakatau by up-rushing steam, which formed by boiling of groundwater below the volcano by the heat of magma as it approached the surface.
The start of the truly giant eruptions were marked by appearance of stiff, viscous, 900 degrees C magma at the surface that was so highly gas-charged that it exploded out of the volcano with the force of hundreds of nuclear bombs. This explosion, known as an �Ultra Plinian� eruption (after Pliny the elder who witnessed much smaller but similar in appearance phenomena during the AD79 eruption of Vesuvius), drives pumice, ash, and gas as a jet out of the volcano, the jet rising to about 50 km into stratosphere. The speed of up-rushing gas, pumice, and ash likely exceeded the speed of sound, and the jet pushed a shock wave into the atmosphere that raced ahead of the jet at a speed of nearly twice that of sound (~650 m/s). The jet emplaced pumice and ash into the atmosphere at a rate of 100 to 1000 million kg per second, much of it falling from high in the sky to blanket surrounding lands under meters of pumice and ash (light blue layer in illustration below). The jet of pumice, ash, and gas was so hot that it continued to rise as a buoyant plume high into the stratosphere, where it was entrained in stratospheric winds circling the earth from west to east.
As the Ultra Plinian eruption continued the land under the volcano began to subside, gradually falling into the evacuated part of the magma chamber several km below. With this subsidence, fractures opened around the volcano, allowing sea water to rush into the magma conduit that connected the magma chamber and volcano. This sea water was instantaneously vaporized with additional explosive force, resulting in an eruption called �Phreatoplinian,� which connotes the combination of Plinian eruption with phreatic (near surface) water. The addition of vast quantities of water vapor to the eruption column caused it to collapse on itself, spilling out clouds of ash, pumice, and steam that raced across the surrounding country side at speeds of up to hundreds of meters per second, slowing down to tens of meters per second after traveling about 10 km from the volcano, but continuing to engulf the country side for up to 50 or more km from the volcano. These �pyroclastic flows� completely wiped out all vegetation and any dwelling structures, leaving nothing alive in their wake.
After days to weeks of these Phreatoplinian eruptions, the volcanic fury subsided, leaving a collapse caldera filled by the sea, separating Sumatra from Java, with vestiges of Proto Krakatau barely peeking above the newly formed Sunda Straits
The following before and after cross sections show how the earth�s surface collapsed downward during the 6th century caldera eruption, producing the Sunda Straits, where the Proto Krakatau volcano collapsed below sea level. Note how rock layers and units, shown in various colors, have been displaced downward after the eruption, and a gray-colored layer blankets the topography denoting the pyroclastic flow deposits left by the eruption. The simulated caldera is over 40 km in diameter.
The next illustration shows the 3-D plan view of the simulation results, a view from high altitude above Sumatra and Java. The simulation shows a rough portrayal of the Sumatra-Java island land mass extending from west to east, with the volcanic cone of Proto Krakatau near the center. This island was constructed by the simulated growth of overlapping volcanic cones and lava plateaus, but does not exactly match the coastline of pre-6thcentury Sumatra and Java. Note that after the 6th century eruption, Proto Krakatau has mostly disappeared, falling below sea level, replaced by a body of water separating Sumatra and Java called the Sunda Straits. From the cross section views above, one can see that the straits are shallow, just covering the sunken volcano. Below, parts of the volcano still protrude above sea level, leaving islands in the straits that are remnants of Proto Krakatau. Perhaps the southern island in the view below is where modern Krakatau will form. Since the 6th century erosion has likely caused some of these islands to fall below sea level, while new volcanic extrusions along the caldera margins have produced new islands, including the present-day Krakatau, which has grown along the southern margin of the caldera. One may also notice a slight change in the coastlines of Sumatra and Java outside of the caldera limits (dotted curve); this change reflects a regional subsidence after the caldera eruption. Although these simulation results are not an exact portrayal of the Sunda Straits, they serve to illustrate the general development of land masses.
Analyzing the Eruption
While the preceding eruption simulations give a good qualitative picture of how the eruption progressed, we desire more detailed information, specifically regarding the physical parameters of the eruption. Some of these parameters can be constrained by considering the scale of the eruption portrayed above, while others must be calculated. Using the results of supercomputer simulations that solve mathematical equations that express the physical behavior of the eruption, we obtain results that are useful for atmospheric and sound wave models.Eruption Duration: From the size of the assumed caldera, we showed above that ~200 km3 of magma was erupted. For eruptions of this magnitude, scaling of smaller historical eruptions indicates mass discharge rates of 1 billion kg per second or more. This flux is equivalent to one-one thousandths of a km3 per second or 3.6 km3 per hour. All other parameters being equal, the eruption would have taken at least 34 hours, but owing to waxing and waning fluxes during the eruption, the cataclysmal parts of the eruption might have lasted over 10 days. In fact, such eruptions might occur in day-long pulses, occurring over a period of years.
Eruption Products: Most of magma was fragmented by the tremendous forces of the eruption into pieces of pumice and ash. Especially during the Phreatoplinian eruption, ash was the preferred form of expelled magma. This ash is composed of tiny fragments of rock and glass shards, ranging from about 1 micrometer to a couple of millimeters in diameter. During the Phreatoplinian eruption, as much as 50% of this ash could have been composed of fragments less than 50 micrometers in diameter. Such tiny fragments have exceedingly long resident times in the atmosphere, able to be kept aloft for months by normal atmospheric turbulence. Assuming that 75% of the total 125 km3 of magma were involved with the Phreatoplinian eruption, perhaps as much as 30 km3 of fine ash particles were put into global circulation. Sulfur from the magma likely condensed on ash particles as sulfuric acid droplets, but its abundance is not known.
Water Vapor: Along with the pumice and ash, a lot of water was vaporized and injected into the atmosphere and stratosphere, especially during the Phreatoplinian phase of the eruption, perhaps volumetrically the most important of the cataclysmal phases. For optimum water vaporization, molten magma contains enough heat to vaporize an approximately equal volume of water. Assuming that 75 of the total 125 km3 of magma interacted with water, 75 km3 were vaporized, which upon expansion to atmospheric pressure may have occupied nearly 100,000 km3 of the atmosphere. To be sure, much of this vapor would have condensed an fallen out as ash-clogged rain with in hours of the eruption, but perhaps as much as half of it was carried around the world by stratospheric winds. This vapor would have condensed to form ice crystals, and these ice crystals would disperse in the rarified air to form stratus clouds, darkened by entrained ash. Along with the water vapor from the sea chlorine is also carried into the stratosphere, a component having an important effect on stratospheric chemistry.
Jet and Plume Structure: The jet of ash, pumice, and gas emerged from the vent at supersonic speeds of 650 m/s but decelerated to slow buoyant rise speeds of several tens of meters per second after reaching 10 to 15 km into the atmosphere. The buoyant plume had sufficient energy to continue rising to nearly 50 km before it became neutrally buoyant and began spreading laterally. The width of the jet and plume during the Plinian eruption phase may have ranged from several km at its base to many as many as 40 km near its apex, just below the level where it spread out as a giant anvil-shaped cloud. Ash concentrations within the plume decreased upwards because of admixture of ambient air into the plume as it rose, but these concentrations probably stayed at levels of 1 part in a million by volume. This is a very conservative estimate of total plume volume over the course of the eruption, giving a value of well over 100 million km3 and likely reaching several orders of magnitude larger.
Summary:
Magnitude
- Collapse of 100 m over 50-km diameter caldera can involve eruption of ~200 km3 of magma
- Scaling of similar-sized eruptions predicts mass fluxes of ~109 kg s-1
- Eruption of 200 km3 of magma at 109 kg s-1 requires at least ~60 hours of continuous eruption
- Continuous eruption not likely, so duration may have lasted from a week to over one month
- Dominantly pumice and ash
- For phreatoplinian eruption up to 50 wt-% of the tephra can be fragmented to fine ash (< 63 mm)
- If 75 vol-% of the erupted products were phreatoplinian, 75 km3 of fine ash were injected into the atmosphere
- Dominantly H2O
- For strong water/magma interaction, a volume of water vaporized is nearly equal to the volume of magma in the interaction
- If 75 vol-% of the erupted products experience strong water/magma interaction then 150 km3 of seawater were vaporized, creating up to 200,000 km3 of water vapor in the atmosphere
- Likely a large portion (50 vol-% or more) condensed an precipitated from low altitudes
- Remaining vapor likely formed ice crystals in the stratosphere
- Erupted at speeds up to 650 m s-1, the eruption column may have exceeded 50 km in height before reaching neutral buoyancy
- From numerical models, tephra volume concentrations after mixing with the atmosphere are 10-6 or less
- If the fine-ash component remained in the plume with water vapor that formed ice crystals, then the total plume volume may have reached several tens of million of km3
Atmospheric Wonderings
- Consider the large volume of the ash and vapor plume (10 � 80 million km3).
- The earth�s tropopause surface area is ~5.2×108 km2.
- Eruption plume could have produced a cloud layer from 20 to 150 m thick over the entire globe.
- With the plume source near the equator, both north and south hemispheres would be affected.
- Such a large magnitude volcanic plume has never been considered for CGMs, and its only analog might be the ejecta plume of the K-T impact.
- Application of nuclear winter models (soot) for the K-T impact indicate such a burden of particles in the stratosphere would cause collapse of the troposphere.
- In addition the large volume of water vapor may produce huge stratospheric ice clouds, leading to destruction of the ozone.
- Initial global cooling by 5 to 10 degrees C or more lasting up to 10 years, caused by the increased global albedo.
- Subsequent global warming with remaining water vapor acting as a greenhouse gas and decreased ozone.
- An artistic rendition of the hypothetical cloud drifting first westward in the tropics and then mixing to higher latitudes to where it spread eastward eventually covering a large portion of the earth’s surface within days and weeks after the eruption (below).
- The frequency of magnitude 8 eruptions is not considered historical
- A 535 Krakatoa (?) suggests a larger frequency of magnitude 7-8 eruptions
- Large, historic caldera-type eruptions may not be recognized because of their location in shallow seas or concealed by vegetation
- In 1998 Stanley Ambrose proposed a volcanic winter hypothesis for recent human DNA differentiation
- Mitochondrial DNA is passed on by mother; the rate of its mutation is fairly constant over time
- Small variation found in today�s population and the number of mutations suggest common ancestors dating back ~70-80 ka (Toba�s eruption)
- A �bottleneck� of this DNA suggests reduction of world population to a few thousands (Rogers and Jorde)
- Do existing lines carry a �survival� signature?
- The historical and archaeological evidence is abundant and so far has stood up to academic review. In fact this evidence is now a major topic for Dark Ages societies
- The Proto-Krakatau hypothesis is supported by somewhat more circumstantial evidence
- The global atmospheric impact is very hypothetical, requiring new GCM model to approach a perturbation of this magnitude
- The global consequences to humanity of a super eruption (Catastrophe) are much more complex and far reaching than has ever been considered. Such an event can fundamentally and permanently change human history
- There are numerous potentially active calderas that can erupt in the near future with the magnitude of Proto-Krakatau
- The global climate impact might involve:
- Initial global cooling by 5 to 10 degrees C or more lasting up to 10 years, caused by the increased global albedo.
- Subsequent global warming with remaining water vapor acting as a greenhouse gas and decreased ozone.
- An artistic rendition of the hypothetical cloud drifting first westward in the tropics and then mixing to higher latitudes to where it spread eastward eventually covering a large portion of the earth’s surface within days and weeks after the eruption (below).
VEI Frequency Plot Revision
- The frequency of magnitude 8 eruptions is not considered historical
- A 535 Krakatoa (?) suggests a larger frequency of magnitude 7-8 eruptions
- Large, historic caldera-type eruptions may not be recognized because of their location in shallow seas or concealed by vegetation
Is Adaptation to Volcanic Crisis Programmed in our DNA?
- In 1998 Stanley Ambrose proposed a volcanic winter hypothesis for recent human DNA differentiation
- Mitochondrial DNA is passed on by mother; the rate of its mutation is fairly constant over time
- Small variation found in today�s population and the number of mutations suggest common ancestors dating back ~70-80 ka (Toba�s eruption)
- A �bottleneck� of this DNA suggests reduction of world population to a few thousands (Rogers and Jorde)
- Do existing lines carry a �survival� signature?
Conclusions
- The historical and archaeological evidence is abundant and so far has stood up to academic review. In fact this evidence is now a major topic for Dark Ages societies
- The Proto-Krakatau hypothesis is supported by somewhat more circumstantial evidence
- The global atmospheric impact is very hypothetical, requiring new GCM model to approach a perturbation of this magnitude
- The global consequences to humanity of a super eruption (Catastrophe) are much more complex and far reaching than has ever been considered. Such an event can fundamentally and permanently change human history
- There are numerous potentially active calderas that can erupt in the near future with the magnitude of Proto-Krakatau