946 eruption of Paektu Mountain

The 946 eruption of Changbaishan, on the boundaries of China/Korea, was one of the most powerful in recorded history and is classified as a VEI-7 event. The eruption resulted in a brief period of significant climate change in China. The age of eruption has not been well constrained, but a possible age is A.D. 946.[1] The 946 eruption of Changbaishan named "Millennium eruption", and erupted about 100–120 km3 tephras.[2][3] Millennium eruption begin with strong Plinian column, and ended by voluminous pyroclastic flow. Average of 5 cm of Plinian ashfall and coignimbrite ashfall covered Sea of Japan and northern of Japan about 1.5 million km2,[2] and the ash layer named "Baegdusan-Tomakomai ash"(B-Tm). Millennium eruption probably occurred in winter of A.D. 946.[4]

Age of Millennium eruption

Age of eruption has not been well constrained. The earliest radiocarbon ages of the carbonized woods yielded three different ages: 1,050 ± 70 B.P., 1,120 ± 70 B.P., and 1410 ± 80 B.P.[4]

History of 14C wiggle-matching dating

In 1996, Dunlap reported a high-precision wiggle-matching age determined at the University of Arizona as 1039 ± 18 AD(2σ).[5] However, in 1998, Liu reported a 14C measurements from the center to the edge of the wood, followed by fitting with a high-accuracy tree ring calibrating curve, the obtained age of the Millennium eruption was determined to be 1215 ± 15 AD.[6] In 2000, Horn reported another wiggle-matched radiocarbon dating with an AMS-mass spectrometer, and the interval of highest probability is 969 +24/-15 AD(945–984 AD; 2σ), which is widely used. In 2000s, at least 5 of high-precision 14C wiggle-matching ages had been reported: 930–943 AD, 926 ± 10 AD, 945–960 AD, 931 ± 10 AD, and 946 ± 6 AD.[1][7][8][9][10]

Recent 14C wiggle-matching dating

Xu et al.,(2013)[1] reported 27 best wiggle-match dating from single partially charred 264-year-old tree, which is 946 ± 3 AD(1σ). Yin et al.,(2012) also reported 82 best wiggle-matched AMS 14C ages of samples from four carbonized logs, which is 938/939. However, the result of Xu et al. (2013)[1] using a “regional 14C offset” in their ages to decrease the error, and their new date was obtained from the longer tree-ring sequence with the higher analytical precision of ±25 14C years, on a 260-year tree-ring sequence that covers three consecutive wiggles around A.D. 910, A.D. 785, and A.D. 730. Since longer dated tree-ring sequence, finer sample resolution, and higher 14C analytical precision all facilitate more and tighter tie-points for better WM dating. The new date is believed to represent yet the best high-accuracy and high-precision 14C WM chronology for the Millennium eruption.[1] Xu's wood samples were cut from a tree growing in the area about 24 km from the vent of Changbaishan volcano, it is not clear if volcanic CO2 emission before the eruption could affect the samples and produce ages that are slightly too old.[1] The best WM dates for the Millennium eruption use the outliers-removed subset of the original 14C measurements and also account for the effect of possible regional 14C offset, and yielded two nearly identical WM ages of A.D. 945 ± 3 and A.D. 947 ± 3, where overall and combined agreement indices of the models reach their highest values.[1] Therefore, the average of these two WM ages (A.D. 946 ± 3) represents the best modeled WM age for the Millennium eruption.[1]

History record

The book «高丽史»(History of Goryeo) describe "是歳天鼓鳴赦" and "定宗元年天鼓鳴"(thunders from the heaven drum) in 946 A.D. Also, the book «興福寺年代記»(Heungboksa Temple History) recored "十月七日夜白灰散如雪"(3 November, white ash rain as snowing) on 3 Nov, 946.[4] The thunders may relate to Millennium eruption, and white ash rain may relate to B-Tm ash.[4] Three months later, on 7 February(947 A.D.), "十四日，空中有聲如雷鳴"(drum thunders) and "正月十四日庚子，此日空中有声，如雷"(drum thunders) were recorded in «貞信公記» and «日本紀略».[4] Another similar recored is on 19 Feb, 944, in «日本紀略» "廿三日丙申，子刻，振動，聲在上".[4] Based on history record, Millennium eruption might started on Feb, 944 or Nov, 946, and the climax eruption may occur on Feb, 947.[4]

Ice-core

Sun et al.,(2013)[11] found volcanic glass in Greenland, which the chemical is good agree with Millennium eruption magma(rhyolite and trachyte). The age of volcanic glass layer is 939/940 A.D. However, Sigl et al.,(2015)[12] found out that ice-core chronologies are 7 years offset, and the Millennium eruption glass layer should be in 946/947 A.D. This conclusion is consistent with wiggle-matching dating and history recored.

Eruption Volume

The eruption volume is also not been well constrained, from 70 to 160 km3. Machida et al.,(1990)[13] roughly estimated the proximal volume(include ignimbrite and Plinian fall) no more than 20 km3, and the volume of distal B-Tm ashfall attains more than 50 km3. The total bulk volume estimate to be 70 km3. Horn and Schmincke (2000)[2] used exponential method for minimum area/thickness and maximum area/thickness obtain the volume of Plinian ashfall is 82 ± 17 km3, and used area-thickness method for ignimbrite obtain 14.9 ± 2.6 km3. The total bulk volume estimate to be 96 ± 19 km3. Liu et al.,(1998)[3] also used same method with Horn and Schimincke to calculate the volume of Plinian ashfall, and obtain almost same value, which is 83 km3. However, Liu used different area-thickness value for ignimbrite. Liu assumed the distribution of ignimbrite is in radius 40 km of caldera, and the average ignimbrite thickness is 7.47m, which the volume of ignimbrite is 37.5 km3. The total bulk volume estimate to be 120 km3. Guo et al.,(2001)[14] used the exponential method estimate that volume of ashfall is 135.2 ± 7.8 km3. But Guo assumed the geometry of ignimbrite is a cone, and the volume of ignimbrite could be 20.1 km3. Guo also calculated the volume of valley-ignimbrite, because in a valley the thickness of ignimbrite could be 80 m. Then, the total bulk volume is 161.6 ± 7.8 km3. However, 100–120 km3 has been widely used.[15]

Eruption dynamic

Base on sequence of pyroclastic, Millennium eruption begins with pumice and ash falls, and then eruption column collapse formed ignimbrite. The column collapse probably is pulsing collapse, because the ignimbrite and pumice-fall are interbedded. Machida et al.,(1990)[13] divided the Millennium eruption into 4 stages: Baegdu Plinian pumice fall, Changbai pyroclastic flow, Yuanchi tephra falls, and Baishan pyroclastic flow. But Baishan pyroclastic flow may related to post-caldera activity (?A.D.1668 eruption?).[15] More recent study indicate that eruption include 2 stages: Plinian pumice fall and unwelded ignimbrite.[2][3]

Plinian stage

This stage formed large area of white comenditic pumice and ash. The Plinian eruption column reached 36 km.[3] B-Tm ash and "white ash rain" may related to this stage.[4] Base on variation of grain-size and thickness of pumice. Plinian stage can divided into 3 part: early period, climax period, and later period.[3]

Early period

In a Plinian pumice-fall sectional, the grain-size of pumice shows reversely graded(coarse pumice on bottom and fine pumice on top). The variation of pumice size shows a major fluctuation in eruption column height during this Plinian event. Base on distribution of maximum lithics clasts, in the early eruption, eruption column probably reached 28 km (HB=20 km), and mass discharge rate attain 108 kg/s (105 m3/s). Early period may released 1.88–5.63 × 1019 joule, and eruption might lasted for 33.5–115.5 hours.[3]

Climax period

Based on distribution of crosswind of maximum lithics clasts, the top of eruption column might reached 36 km (HB=25 km), and mass discharge rate attain 3.6 × 108 kg/s (3.6 × 105 m3/s). The distribution of downwind of maximum lithics clasts shows wind direction is SE120°, and the wind speed is 30 m/s during the climax period. For radius of eruption vent, the height of eruption column (HB=25 km), the H2O content of magma (1–2%), and the temperature of magma (1000 k) indicate that radius of eruption vent is 200 m. Climax period may released 4.18–12.43 × 1019 joule, and eruption might lasted for 35–104 hours.[3]

Later period

This period eruption formed the upper part of Plinian pumice fall, which is the fine pumice. Later Plinian pumice fall and pyroclastic flow are at same time, because some sectional shows that pumice fall and ignimbrite are interbedded. Combine the grain-size of pumice and thickness of pumice fall. The height of eruption column of later period is no higher than 14 km (HB=10 km), and the mass discharge rate is 5 × 106 kg/s (5 × 103 m3/s). Later period may released 8.76–26.16 × 1017 joule for Plinian eruption and keeping eruption column.[3]

Ignimbrite stages

In many sectional, a large grey ground-surge under an ignimbrite sheet, which might be a front part of pyroclastic flow, and the unwelded ignimbrite always underlain a large ash-cloud surge. They are part of ignimbrite. Ignimbrite distributed in radius 40 km of caldera, and average thickness is 7.47 m. In many valleys, thickness of ignimbrite may be 70–80 m. Changbaishan ignimbrite is low-aspect ratio ignimbrite, which is 1.87 × 10−4. Speed of initial pyroclastic flow might be 170 m/s (610 km/h), and 50 m/s (180 km/h) in 50 km away from the caldera.[3]

Duration

The radius of vent and H2O content of magma indicate that average of volume discharge rate of Plinian eruption and ignimbrite is 1–3 × 105 m3/s (1–3 × 108 kg/s). Assume the total bulk volume of Millennium eruption is 120 km3, and bulk volumes of pumice fall and ignimbrite are 83 km3 and 37.5 km3, respectively. Ignimbrite-forming eruption may lasted one and a half day to four days (35–104 hours). Plinian eruption may lasted three days to nine and a half days (77–230 hours). The duration of Millennium eruption may be four and a half days to fourteen days (111–333 hours).[3]

Volatile

Plinian volcanic eruptions could inject a large amount of volatiles and aerosols into atmosphere, even stratosphere, leading to climate and environment changes.[14] Chlorine concentrations in the peralkaline from Millennium eruption were postulated to have reached up to 2% and an average of 0.44%. The Millennium eruption was thus thought to have emitted an enormous mass of volatiles into the stratosphere, potentially resulting in a major climatic impact.[2]

Cl

McCurry used electron microprobe analysed the volatile in glass inclusion of feldspar, the result of electron microprobe analysis shows 1% halogen, and he assumed the degassing efficiency factor of peralkaline is 0.3–0.5. McCurry concluded that Millennium eruption may released 2000 Mt Cl.[16] Liu used chromatography to analysed the average of volatile of 5 whole-rock samples, and the contents of halogen is 0.08%–0.11%.[16] More recent and more details study is Horn and Schmincke (2000).[2] They used ion probe to analysed the average of volatile in 6 of matrix glass and 19 melt inclusions, and the average of content of Cl in melt inclusions and matrix glass are 0.4762% and 0.3853%, respectively. Horn and Schmincke concluded that Millennium eruption may released 45 ± 10 Mt of Cl. Another author Guo[14] who study petrology and geochemistry shows the average of contents of Cl in melt inclusions and matrix glass are 0.45% and 0.33%, respectively.[14] They concluded that Millennium eruption may released 109.88 Mt of Cl, and 15.82 input to stratosphere.[14] The Cl contents in the melt inclusions are similar to those of Mayor Island, and higher than those of Tambora (0.211%), Krakatau (0.238%) and Pinatubo (0.88–0.106%).[2][14] The large difference of results between Guo and Horn is because Guo used higher volume and density of magma.

SO2

Liu used chromatography to analysed the average of volatile of 5 pumice and obsidian, and the contents of S are 0.0415%, and Liu assumed the degassing efficiency factor of S is 0.3. Liu estimated that Millennium eruption may released 40 Mt of SO2.[16] However, Horn and Schimincke[2] calculated that only 20% S in magma had been degassed, because 80% of all analyses of inclusions and matrix fall below the detection limit of ion probe. The results of average contents of S in 19 of inclusions are 0.0455%, Horn assumed the contents of S in matrix glass are 0.025% because 250 ppm is detection limit of ion probe.[2] They concluded that the total SO2 released from eruption are only 4 ± 1.2 Mt, but Horn suggests that may be excess sulfur accumulated in vapor phase.[2] Guo calculated the average contents of S in 9 glass inclusions and 1 matrix glass are 0.03% and 0.017%, respectively. The results of Guo are 23.14 Mt of SO2 released from eruption, and 3.33 Mt of SO2 input to stratosphere.[14] The S contents in glass inclusions show the reverse correlation with SiO2 concentrations, indicating that S solubility in magma is controlled by magma differentiation process because of occurrence of the S-rich fluid inclusions.[14]

F

Liu used chromatography to analysed the average of volatile of 5 pumice and obsidian, and the contents of F are 0.0158–0.0481%. Horn and Schimincke used ion probe found that average contents of F in inclusions are 0.4294%, but F concentrations in matrix glass show a significant bimodal distribution into F-rich (0.3992% F) and F-poor (0.2431% F).[2] In order not to over-estimate syn-eruptive F loss, they considered this bimodal distribution of F for calculating the volatile difference between matrix glass and melt inclusions (4300 ppm F). The volatile loss is approximately 300 ppm F for melt inclusion and F-rich matrix glass (64% proportion of the comenditic magma), whereas it is 1900 ppm F for melt inclusion and F-poor matrix glass (36% proportion of the comenditic magma). Horn concluded that 42 ± 11 Mt of F released from eruption.[2] Guo base on less samples (9 inclusions and 3 matrix glass) calculated that F contents in inclusions and matrix glass are 0.42% and 0.21%, respectively.[14] Guo concluded that 196.8 Mt of F released from eruption, and 28.34 Mt of F input to stratosphere.[14] With magma evolving, halogen contents increase irregularly, parallel to the increase of SiO2 concentrations in glass inclusions[14] The large difference of results between Guo and Horn is because Guo used higher volume and density of magma, and higher difference contents between matrix glass and inclusions.

Vapor phase

Sulfur is not strongly enriched during differentiation, in contrast to water, chlorine, and fluorine. The reason could be pre- or syn-eruptive degassing of a separate vapor phase, such as postulated for the Pinatubo and Redoubt eruptions. The ultimate source for the excess volatile observed during the 1991 Pinatubo eruption is assumed to be sulfur-rich basaltic magmas underlying, and syn-eruptively intruded, into the overlying felsic magmas. The sulfur-rich trachytic and trachyandesitic magmas which underlay the rhyolitic magma at Changbaishan may have been a possible source for excess sulfur accumulation. If this scenario is realistic, clearcut proxies for the environmental impact of the eruption would be expected.[2][14] Millennium eruption magmas are predominantly phenocryst-poor (≤ 3 vol%) comendites plus a volumetrically minor late-stage, more phenocryst-rich (10-20 vol%) trachyte. Sizeable (100-500 µm diameter) glassy but bubble-bearing melt inclusions are widespread in anorthoclase and hedenbergite phenocrysts, as well as in rarer quartz and fayalite phenocrysts. Comparing the relative enrichments of incompatible volatile and non-volatile elements in melt inclusions along a liquid line of descent shows decreasing volatile/Zr ratios suggesting the partitioning of volatiles into a fluid phase. This suggests that current gas-yield estimates (Horn & Schminke, 2000[2]) for the Millennium eruption, based on the petrologic method (difference in volatiles between melt inclusions and matrix glass), could be severe underestimates.[17]

Climate impact

Millennium eruption was thus thought to have emitted an enormous mass of volatiles into the stratosphere, potentially resulting in a major climatic impact, but more recent study indicate that the Millennium eruption of Changbaishan volcano might have limited regional climatic effects, rather than global or hemispheric impact as implied by its magnitude.[1][2][11][12] However, there are some temperature anomaly and atmospheric anomaly in A.D. 945–948 may related to Millennium eruption.[18][19]

Date Temperature Anomaly Atmospheric Anomaly Source
4. Apr, 945 It snowed heavily Old History of the Five Dynasties
28. Nov, 946 Glaze ice Old History of the Five Dynasties
7. Dec, 946 Large scale frost and fog, and rime covered all plants Old History of the Five Dynasties
31. Jan, 947 It snowed over ten days, and caused inadequate food supply and famine Old History of the Five Dynasties, Zizhi Tongjian
24. Feb, 947 until 23. Apr, 947 Warm spring Japanese historical meteorological materials
14. May, 947 Frost, and cold as harsh winter Japanese historical meteorological materials
28. Nov, 947 On the sun there was a black spot like a hen's egg Old History of the Five Dynasties
16. Dec, 947 Glaze ice Old History of the Five Dynasties
25. Dec, 947 Glaze ice Old History of the Five Dynasties
6. Jan, 948 Glaze ice Old History of the Five Dynasties
24. Oct, 948 It snowed in Kaifeng Old History of the Five Dynasties

References

  1. 1 2 3 4 5 6 7 8 9 Xu, JD (2013). "Climatic impact of the Millennium eruption of Changbaishan volcano in China: New insights from high-precision radiocarbon wiggle-match dating". Geophysical Research Letters 40: 54–59. Bibcode:2013GeoRL..40...54X. doi:10.1029/2012GL054246.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Horn, S (2000). "Volatile emission during the eruption of Baitoushan Volcano (China/North Korea) ca. 969 AD". Bull Volcanol 61: 537–555. doi:10.1007/s004450050004.
  3. 1 2 3 4 5 6 7 8 9 10 L'iu, RX (1998). Modern eruption of Changbaishan Tianchi volcano. China Science Publishing.
  4. 1 2 3 4 5 6 7 8 Hayakawa, Y (1998). "Dates of Two Major Eruptions from Towada and Baitoushan in the 10th Century". Bulletin of the Volcanological Society of Japan.
  5. ↑ Dunlap, C (1996). "Physical, chemical, and temporal relations among products of the 11th century eruption of Baitoushan, China/North Korea".
  6. ↑ Liu, RX (1998). "The date of last large eruption of Changbaishan-Tianchi volcano and its significance". Science in China Series D: Earth Sciences 41: 69–74. doi:10.1007/BF02932423.
  7. ↑ Nakamura, F (2007). "High-precision radiocarbon dating with accelerator mass spectrometry and calibration of radiocarbon ages". The Quaternary Research.
  8. ↑ Machida, H (2007). "Recent large-scale explosive eruption of Baegdusan volcano: age of eruption and its effects on society".
  9. ↑ Yatsuzuka, S (2010). "14C wiggle-matching of the B-Tm tephra, Baitoushan volcano, China/North Korea". Radiocarbon.
  10. ↑ Yin, J (2012). "A wiggle-match age for the Millennium eruption of Tianchi Volcano at Changbaishan". Quaternary Science Reviews 47: 150–159. doi:10.1016/j.quascirev.2012.05.015.
  11. 1 2 Sun, CQ (2013). "Ash from Changbaishan Millennium eruption recorded in Greenland ice: Implications for determining the eruption’s timing and impact". Geophysical Research Letters 41: 694–701. doi:10.1002/2013GL058642.
  12. 1 2 Sigl, M (2015). "Timing and climate forcing of volcanic eruptions for the past 2,500 years". Nature 523: 543–549. doi:10.1038/nature14565.
  13. 1 2 Michida (1990). "The recent major eruption of changbai volcano and its environmental effects".
  14. 1 2 3 4 5 6 7 8 9 10 11 12 Guo, ZF (2001). "The mass estimation of volatile emission during 1199–1200 AD eruption of Baitoushan volcano and its significance". Science in China Series D: Earth Sciences 45: 530. doi:10.1360/02yd9055.
  15. 1 2 Wei, HQ (2013). "Review of eruptive activity at Tianchi volcano, Changbaishan, northeast China: implications for possible future eruptions". Bull Volcanol 75. doi:10.1007/s00445-013-0706-5.
  16. 1 2 3 Liu, RX (1998). Volcanism and human environment. Seismological Press. p. 11. ISBN 7502812504.
  17. ↑ Iacovino, K (2014). "Evidence of a Pre-eruptive Fluid Phase for the Millennium Eruption, Paektu Volcano, North Korea". American Geophysical Union. Bibcode:2014AGUFM.V24D..08I.
  18. ↑ Fei, J (2006). "The possible climatic impact in China of Iceland's Eldgja eruption inferred from historical sources". Climatic Change 76: 443–457. doi:10.1007/s10584-005-9012-3.
  19. ↑ Yau, KKC (1988). "A revised catalogue of far eastern observations of sunspots (165 BC to 1918 AD)". Royal Astronomical Society. Bibcode:1988QJRAS..29..175Y.

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