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The 1669 eruption at Mount Etna: Chronology, petrology and geochemistry, with inferences on the magma sources and ascent mechanisms

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 Analysis of the petrochemical characters of the 1669 Etnean lavas shows that they can be grouped into two sets: SET1 lavas were erupted from 11 to 20 March and are more primitive in composition than SET2, erupted later until the end of activity. Both sets may be interpreted as the result of crystallization under different conditions of two primary magmas which are compositionally slightly distinct and which fractionate different volumetric proportions of minerals. To explain why more mafic lavas (SET1) were erupted earlier than more acid ones (SET2), we argue that new deeper magma rose up into a reservoir where residing magma was fractionating. Density calculations demonstrate that new magma is less dense and may originate a plume, rapidly rising through the residing magma which is cooler and more volatile-depleted than the new magma. Calculations of uprise velocity assuming laminar flow are consistent with this hypothesis.
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Editorial responsibility: M. Rosi
Rosa Anna Corsaro 7 Renato Cristofolini (Y)
Loredana Patanè
Istituto di Scienze della Terra, University of Catania,
C.so Italia, 55, I-95129 Catania, Italy
Fax: c95 719 5760
Bull Volcanol (1996) 58:348–358 Q Springer-Verlag 1996
ORIGINAL PAPER
R. A. Corsaro 7 R. Cristofolini 7 L. Patanè
The 1669 eruption at Mount Etna: chronology, petrology and
geochemistry, with inferences on the magma sources and ascent
mechanisms
Received: 20 November 1995 / Accepted: 2 August 1996
Abstract Analysis of the petrochemical characters of
the 1669 Etnean lavas shows that they can be grouped
into two sets: SET1 lavas were erupted from 11 to
20 March and are more primitive in composition than
SET2, erupted later until the end of activity. Both sets
may be interpreted as the result of crystallization under
different conditions of two primary magmas which are
compositionally slightly distinct and which fractionate
different volumetric proportions of minerals. To ex-
plain why more mafic lavas (SET1) were erupted ear-
lier than more acid ones (SET2), we argue that new
deeper magma rose up into a reservoir where residing
magma was fractionating. Density calculations demon-
strate that new magma is less dense and may originate a
plume, rapidly rising through the residing magma
which is cooler and more volatile-depleted than the
new magma. Calculations of uprise velocity assuming
laminar flow are consistent with this hypothesis.
Key words Lava compositions 7 Magma sources 7
Plume ascent 7 Mount Etna 7 1669 eruption
Introduction
The 1669 eruption at Mount Etna (11 March to 11 July)
was quite unique among the historically dated ones due
to:
1. The relatively low elevation of the vents (800–
850 m a.s.l.)
2. The large volume of lava erupted (500–1000 7
106 m
3
; Wadge 1977; Romano and Sturiale 1982)
3. Its high average effusion rate (p50–100 m
3
/s), which
induced the lava flow branches to run over long dis-
tances, flooding a fairly densely populated area and
threatening several towns and villages, among them
Catania itself, which was partly destroyed.
Because of the impact on the region and its inhabi-
tants, this eruptive event is well documented in papers
based on contemporary records (Recupero 1815; Alessi
1832; Gemmellaro 1860; Sartorius 1880), so that its vol-
canological and petrological evolution may be recon-
structed with some accuracy.
The 1669 eruption is also interesting because it
marks a significant change in the petrography and erup-
tive regime of Mount Etna (Tanguy 1980; Guest and
Duncan 1981; Clocchiatti et al. 1988; Hughes et al.
1990; Condomines et al. 1995). From F1600 to 1669,
effusive activity consisted typically of frequent, long-
lasting and high-volume eruptions of plagioclase-rich
lavas; in contrast, the period 1670–1750 was character-
ized by more sporadic and shorter eruptions of low ef-
fusion rates and lavas richer in mafic phenocrysts.
For this reason we undertook a detailed sampling of
1669 lavas, whose petrochemical, geochemical and iso-
topic study allows us to interpret its pre-eruptive mag-
matic evolution.
The eruption course
The eruption was preceded by more than 2 weeks of
increasing seismic activity (Anonymous 1669 in De
Fiore 1912). Early in the morning on 11 March (at
about 5 a.m.), a 2-m-wide fracture opened, extending
for 9 km from the base of Mt. Frumento (2800 m a.s.l.)
to Piano S. Leo (1200 m a.s.l.), where weak eruptive
episodes occurred. Shortly thereafter on the same day a
new fracture opened from Mt. Nocilla to Mt. Fusara,
with vents erupting juvenile tephra, until the evening
when a lava flow poured out at the site where the main
cinder cone (Monti Rossi) of this eruption was even-
tually to develop in the next few days.
349
Lava flowed around the undated cone of Monpilieri,
with two branches heading to the nearest villages (Mal-
passo to the west and Mascalucia to the east), which
were reached and destroyed, respectively, on 12 March
and 13 March.
From 14 March effusive activity gave rise to a wide
fan-like lava field which subdivided downslope into
three main branches which headed toward the Campor-
otondo countryside, St. Pietro Clarenza and St. Giovan-
ni Galermo, respectively.
The summit crater remained quiet until 25 March
when a violent explosive event occurred (at about
10 a.m.), followed by the partial collapse of the summit
cone.
On 20 March (Anonymous 1669; Tedeschi-Paternò
1669; Winchelsea 1669) a flow unit moved rapidly
southward and then toward the western side of the city
of Catania. After having ponded in a depression (Gur-
na di Nicito) at the end of March, the branch reached
the city walls on 1 April, and later surrounded the high-
standing Ursino Castle, flowing into the sea (23 April)
with a 2-km-wide front.
In the following 2 months, the branch directed to
Catania was continually fed, probably through a lava
tube system, and kept slowly flowing to the sea, up to
17 km away from the vents.
A surface of approximately 37 km
2
was covered by
the flow field and related tephra and approximately ten
towns or villages were destroyed or partly damaged by
the lava flow and by seismic activity preceding and ac-
companying the eruption. A sketch map of the flow
field, with dates and approximate locations of the ad-
vancing fronts, is shown in Fig. 1.
Sampling and analytical techniques
Lavas were sampled along the main 1669 flow
branches; ten samples were taken at various vertical
quarry sections next to the fronts. Because historic re-
cords permit us to reconstruct a temporal sequence of
the different flow branches, the specimens may be as-
signed to the branches active until 20 March (grouped
as SET1) or to the later branch which reached Catania
(grouped as SET2).
Mineral analyses were carried out at “C.N.R.-C.S.
per la Minerogenesi e Geochimica Applicata”, Flor-
ence, by means of a Jeol JXA-8600 electron micro-
probe at an acceleration voltage of 15 kV and a cup
current of 10 mA and corrected according to Bence and
Albee (1968).
Major elements were analysed at the Istituto di
Scienze della Terra, Catania, by X-ray fluorescence
(XRF) on powder pellets except for MgO (AAS), FeO
(KMnO
4
titration), and LOI (gravimetric analyses).
Results are calibrated against several international
standards and reproducibility is better than 0.5% of the
analytical values. Only data from one laboratory, ob-
tained by the same methods, were considered to avoid
effects due to systematic interlaboratory errors.
Fig. 1 Map of the 1669 flow (redrawn from VV AA 1979). Ap-
proximate sites of Catania and villages at the eruption time and
front positions of the advancing branches are shown. Thick gray
line marks probable lava tube system. Inset: triangle summit crat-
ers; 1 Mt. Frumento; 2 Mt. St. Leo; 3 Mt. Nocilla; 4 Mt. Fusara; 5
Mt. Rossi; stippled area sedimentary basement
Trace element contents were measured at Actlabs,
Canada, by inductively coupled plasma emission (ICP;
Sr, Zr, Th, U, V, Y, Cu, Ni) and instrumental neutron
activation analysis (INAA; Rb, La, Sm, Yb, Sc, Cs, Ce,
Eu, Lu, Co, Ta, Nd, Tb, Cr). Analytical uncertainty is
given as lower than 5% for all trace elements except
Tb, Rb, Cs, Ta and Ni whose contents, in analysed lav-
as, are next to instrumental detection limit.
Sr-isotope compositions were measured by means of
VG Micromass 54 E mass spectrometer at Dipartimen-
to di Scienze della Terra dell’ Università “La Sapien-
za”, Rome. Analytical uncertainty is below B0.00003.
Ratios are corrected for mass fractionation relative to
NBS987 standard with
87
Sr/
86
Srp0.71017.
Petrography
Among the analysed lavas, porphyritic varieties are
dominant with porphyricity index (PIptotal pheno-
crysts vol%) in the range 37–52 and phenocryst colour
index (CI
phx
pmafic mineral phenocrysts/total pheno-
crysts vol%) in the range 10–53. Although precision of
350
Fig. 2 Porphyricity index (PIptotal phenocrysts vol%) vs pheno-
cryst colour index (CI
phx
pmafic mineral phenocrysts/total pheno-
crysts vol%). The PI and CI
phx
values measured in rocks be-
longing to SET1 (open squares) are significantly different from
SET2 lavas (filled squares)
modal analysis is much less than for chemical data, two
groups are clearly apparent: average PI (p33) and
CI
phx
(p36) measured in rocks belonging to SET1 are
significantly different from those of SET2 lavas (aver-
age PIp44 and CI
phx
p18), which are similar to the ear-
lier seventeenth century ones (Fig. 2).
All the analysed samples show the mineral associa-
tion plccpx (augite)colcmt (either as phenocrysts or
in the groundmass) which is typical of alkaline Etnean
lavas; glomeroporphyritic textures are common in all of
the examined lavas, with either monomineralic and po-
lymineralic aggregates.
Plagioclase phenocryst compositions vary within a
range (An
56-85
Ab
15-41
Or
1-3
) common to other Etnean
recent lavas (Cristofolini et al. 1987b; Tanguy 1980;
Corsaro 1990). Direct and oscillatory zoning schemes
are common, suggesting variable physical and chemical
conditions during its growth history. Mafic inclusions
and sieve textures are common, which may suggest rap-
id growth due to decompression and volatile loss.
Clinopyroxene compositions plot in the diopside
field of the Wo–En–Fs diagram (Morimoto 1988), like
for previously analysed Recent Mongibello pyroxenes
(Cristofolini et al. 1987b; Corsaro 1990); Al
IV
is high
(0.10 a.u.f.), Al
VI
is consistently low (0.04 a.u.f.) sug-
gesting crystallization at P~0.5 GPa (Mun˜oz and Sa-
gredo 1974). Lack of zoning in olivine phenocrysts
(cores: Fo
73–77
; rims: Fo
73–74
) suggests a subsolidus ho-
mogenization, due to ionic diffusion probably related
to high-temperature re-equilibration.
Ti-magnetite, with TiO
2
contents ranging from 9.9 to
19.24%, is the only opaque mineral, with microlites be-
ing Ti-enriched (Uspp60) relative to phenocrysts
(Uspp40).
Among aggregates, plagioclase clusters, often in syn-
neusis relationship (Vance 1969), are the most com-
mon, with plagioclase crystals having the same size and
compositional range as the isolated ones, which sug-
gests similar growth times and crystallization condi-
tions.
Clinopyroxene aggregates are rare, whereas “gab-
broic” (plcpxcolBmt) aggregates are common with
mineral compositions similar to those of the isolated
crystals.
Chemistry
Analyses of some representative samples and average
major and trace element compositions of both SET1
and SET2 are shown in Table 1.
Major elements
Based on major element compositions determined in
all of the samples, the 1669 lavas fall in the Na-alkalic
field, and are exclusively hawaiites, as clearly shown in
the TAS diagram (Fig. 3; Le Maitre 1989).
Because Mg
v
* values (Mg/MgcFe
2c
normalized for
Fe
2
O
3
/FeOp0.15) are between 55 and 63, no primitive
melt compositions are represented among the sampled
lavas.
The 1669 lava compositions plot across most of the
field of post 1500 Etnean lavas for many elements (Cor-
saro and Cristofolini 1991; Cristofolini and Romano
1982). In Harker diagrams the rock sets previously de-
fined on the basis of their petrography and time se-
quence differ from each other in their chemistry also
and define distinct trends: SET2 lavas quite closely re-
semble the plagioclase-phyric ones of the early seven-
teenth century, whereas SET1 lavas are definitely more
basic and magnesian (Fig. 4), showing a tendency to the
later eighteenth- to early twentieth century products.
The meaning of this distribution is examined later.
Trace elements
Trace element contents, measured on selected samples,
cover the compositional range of 1669 (Barbieri et al.
1993) and other Etnean historical eruptions (Corsaro
1990), and their distribution is coherent with the major
element compositions. Compatible trace element con-
tents (Cr, Ni, Co, Sc) related to mafic phases are syste-
matically higher in SET1 than in SET2 rocks; Sr and Ba
contents (compatible with plagioclase) are systematical-
ly lower in SET1 than in SET2. Incompatible element
contents are generally higher in SET1 than in SET2
(Fig. 5 and Table 1).
Primitive mantle normalized patterns (Hofmann
1988) are quite similar to that of within-plate basalts ex-
cept for some anomalies, negative for Ta and Ti and
positive for Th, as already observed (Beccaluva et al.
1982; Cristofolini et al. 1987a; Armienti et al. 1989; Cor-
saro 1990).
351
Table 1 Major (% weight), trace (ppm) element and Sr itotope composition of some representative samples for SET 1 and SET 2 lavas. Average values and standard deviations are
also shown. Major elements average values are calculated for 10 samples (SET 1) and 24 samples (SET 2); trace elements average values are calculated for 4 samples (SET 1) and 6
samples (SET 2); Sr isotopes average values are calculated for 3 samples (SET 1) and 5 samples (SET 2)
SET 1 SET 2 SET 1 SET 2
Sample 669/19 669/20 669/22 669D 669/01 669/03 669/13 669/14 669/16 669G Mean SD Mean SD
SiO
2
48.97 48.76 48.52 48.45 49.84 49.67 50.50 50.04 50.33 50.14 48.78 0.28 50.24 0.33
TiO
2
1.40 1.38 1.44 1.49 1.30 1.36 1.26 1.31 1.21 1.27 1.42 0.07 1.26 0.08
Al
2
O
3
18.83 18.56 18.14 18.16 19.87 19.42 19.91 19.77 19.84 19.81 18.59 0.47 19.75 0.23
Fe
2
O
3
2.14 3.32 2.26 3.35 1.58 2.40 1.73 1.88 1.93 2.39 3.28 1.07 2.59 1.23
FeO 6.65 5.82 7.29 6.58 6.27 5.79 5.68 5.95 5.44 5.37 5.94 0.93 5.12 0.95
MnO 0.18 0.18 0.19 0.19 0.16 0.18 0.14 0.16 0.16 0.16 0.19 0.01 0.16 0.01
MgO 6.38 6.73 7.01 7.01 5.18 5.20 4.78 4.98 5.20 5.45 6.65 0.38 5.07 0.19
CaO 8.78 8.63 8.81 8.89 9.18 9.41 9.11 9.10 9.02 9.08 8.77 0.11 9.15 0.16
Na
2
O 4.11 4.04 3.95 3.73 4.11 4.00 4.34 4.23 4.27 4.19 4.00 0.12 4.22 0.15
K
2
O 1.39 1.38 1.31 1.33 1.36 1.32 1.46 1.39 1.40 1.39 1.37 0.03 1.39 0.04
P
2
O
5
0.49 0.48 0.48 0.42 0.43 0.41 0.51 0.45 0.50 0.47 0.46 0.03 0.47 0.03
L.O.I. 0.67 0.73 0.60 0.41 0.73 0.84 0.58 0.74 0.69 0.27 0.57 0.13 0.58 0.19
Rb 49.0 40.0 35.0 36.0 30.0 34.0 36.0 39.0 34.0 21.0 40.0 6.0 32.0 6.0
Cs 1.3 1.0 0.8 0.8 0.7 0.7 0.8 0.6 0.8 0.6 1.0 0.2 0.7 0.1
Sr 1058.0 1020.0 990.0 900.0 1288.0 1216.0 1204.0 1228.0 1134.0 1184.0 992.0 67.0 1209.0 51.0
Ba 688.0 660.0 648.0 610.0 700.0 670.0 676.0 688.0 634.0 661.0 652.0 32.0 672.0 23.0
Ta 2.5 2.5 2.6 2.5 2.0 2.5 2.4 2.5 2.7 1.9 2.5 0.1 2.3 0.3
Th 10.0 9.0 9.5 8.3 8.5 8.1 8.7 8.7 8.3 7.8 9.2 0.7 8.4 0.4
U 2.3 2.3 2.5 2.7 2.5 1.7 2.0 1.9 2.2 2.3 2.5 0.2 2.1 0.3
Zr 194.0 210.0 216.0 n.d. 202.0 202.0 192.0 196.0 178.0 199.0 207.0 11.0 195.0 9.0
Hf 5.0 4.5 4.7 4.5 4.2 3.6 4.5 4.2 4.5 4.2 4.7 0.2 4.2 0.3
La 67.7 68.5 71.3 63.1 62.2 62.7 64.3 64.7 67.0 61.0 67.7 3.4 63.7 2.1
Ce 142.0 136.0 124.0 120.0 110.0 127.0 130.0 125.0 128.0 100.0 131.0 10.0 120.0 12.0
Nd 59.0 55.0 55.0 48.0 49.0 51.0 49.0 50.0 51.0 42.0 54.0 5.0 49.0 3.0
Sm 11.0 10.0 9.2 8.3 7.7 9.2 9.5 8.9 9.2 7.2 9.0 1.2 8.6 0.9
Eu 2.60 2.67 2.68 2.39 2.40 2.40 2.45 2.30 2.50 2.27 2.59 0.13 2.39 0.09
Tb 1.2 1.0 1.0 1.0 0.8 0.9 1.0 0.9 0.9 0.9 1.1 0.1 0.9 0.1
Yb 2.49 2.68 2.32 2.03 1.87 2.32 2.26 2.20 2.27 1.72 2.38 28.00 2.11 0.25
Lu 0.36 0.36 0.34 0.32 0.21 0.33 0.35 0.32 0.33 0.27 0.35 0.02 0.30 0.05
Y 16.0 16.0 16.0 n.d. 16.0 14.0 16.0 16.0 14.0 26.0 16.0 1.0 17.0 5.0
Ni 36.0 41.0 45.0 n.d. 26.0 27.0 24.0 24.0 26.0 30.0 41.0 5.0 26.0 2.0
Cr 80.0 86.0 93.0 74.0 50.0 39.0 40.0 43.0 50.0 45.0 83.0 8.0 45.0 5.0
Sc 28.0 28.0 31.0 24.0 23.0 23.0 21.0 21.0 23.0 22.0 28.0 3.0 22.0 1.0
V 229.0 223.0 231.0 n.d. 181.0 187.0 193.0 184.0 187.0 250.0 228.0 4.0 197.0 26.0
Co 45.0 47.0 51.0 46.0 36.0 33.0 35.0 34.0 35.0 34.0 47.0 3.0 35.0 1.0
Cu 120.0 119.0 121.0 n.d. 106.0 107.0 112.0 109.0 108.0 110.0 120.0 1.0 109.0 2.0
87
Sr/
86
Sr 0.70338 0.70341 0.70330 0.70344 0.70341 0.70337 0.70336 0.00006 0.70340 0.00003
352
Fig. 3 TAS diagram (Le Maitre 1989). 1669 lavas fall into Na-
alkalic field, being exclusively hawaiites in composition. (For
symbols see Fig. 2)
Fig. 4 In Harker diagram, 1669 lavas group into two distinct data
sets: SET1 rocks, erupted until 20 March, are more basic than
SET2, erupted after this date. In most of the plots the two sets
project on distinct trends. Error bars are 2s. (For symbols see
Fig. 2)
Strontium isotope distribution
87
Sr/
86
Sr values, measured in samples, range from
0.70330 to 0.70344 (Fig. 6). These values are systemati-
cally lower than those given by Barbieri et al. (1993) for
the same flow because of a different standard value
used for normalizing the data.
As the isotopic variability is generally within analyti-
cal uncertainty (expressed as 2s),
87
Sr/
86
Sr ratios may
then be considered substantially constant, i.e. consis-
tent with an origin of magmas from an isotopically ho-
mogeneous source.
Petrological study
In Harker diagrams the analysed rocks define two dis-
tinct trends which, on the whole, may not be referred to
a continuous crystal fractionation process from a
unique parent magma under homogeneous conditions,
because there is no simple way to account for a transi-
tion from SET1 to SET2 compositions by fractionation
of phases consistent with the actual mineralogy. In
greater detail the SET1 trend appears as chiefly related
to the role played by mafic phases (cpx, mt, ol), and the
SET2 variation as chiefly controlled by sialic phases
(plagioclase).
The two rock sets may be further distinguished from
each other if major element compositions are plotted
into the pseudo-ternary diagram Ol–Di–Ne (Fig. 7;
Sack et al. 1987), where they define distinct elongated
fields with their major axes subparallel to each other
353
Fig. 5 Trace element contents
(ppm) of selected samples. Er-
ror bars are 1s. (For symbols
see Fig. 2)
Fig. 6
87
Sr/
86
Sr values of selected samples belonging to both
SET1 and SET2. Since the variance is less than analytical uncer-
tainty, the isotopic ratios may substantially be considered homo-
geneous. Error bar is 2s. (For symbols see Fig. 2)
Fig. 7 In pseudo-ternary diagram Ol–Di–Ne (Sack et al. 1987),
1669 lavas define distinct elongated fields with their major axes
subparallel to each other and to the high (8–30 kbar) and low
(1 bar) pressure cotectict lines, implying no simple relationship
between the two sets. (For symbols see Fig. 2)
and to the high (8–30 kbar) and low (1 bar) pressure
cotectict lines, implying no simple relationship between
the two sets.
Fractional crystallization hypothesis: a test
To assess the importance of fractional crystallization
within SET1 and SET2, we modeled the compositional
variation using the XLFRAC program (Stormer and
Nicholls 1978), by one step for each of the two sets,
with involved phase compositions measured by micro-
probe (Table 2A). Step A: 669/22–669/20: to mimic the
SET1 trend. Step B: 669/3–669/13:to mimic the SET2
trend.
In each step the pair is chosen so that most of the
compositional range of the related set is covered. Ta-
ble 2B shows the mass balance calculation results.
In order to explain the different compositions of
669/22 and 669/20, only 3% of solid mafic phases (one
tenth of the actual phenocryst content) should be re-
moved: 1.8% cpx, 0.6% mt and 0.6% ol, which does not
look consistent with a major role played by crystal frac-
tionation. On the other hand, to drive composition
from 669/3 to 669/13, 7% of solid phases should be re-
moved, among which plagioclase takes a relevant role
(2.3%).
Also, trace element mass balance calculations using
a Rayleigh crystallization model for the same two steps
discussed above, with bulk distribution coefficients
from Villemant et al. (1981), match fairly well the ma-
354
Table 2
A) Phenocryst compositions measured by microprobe
Pl Ol Cpx Mt
SiO
2
TiO
2
Al
2
O
3
FeO
tot
MnO
MgO
CaO
Na
2
O
K
2
O
47.56
0.00
32.50
0.81
0.07
0.36
15.87
2.67
0.07
37.51
0.11
0.00
22.36
0.42
38.44
0.35
0.84
0.10
48.59
1.62
5.06
8.53
0.19
12.56
22.39
0.97
0.00
0.64
13.19
5.91
70.02
0.75
3.50
0.54
0.00
0.18
B) Mass balance results for major elements (Stormer and Nicholls
1978)
Steps Pl Ol Cpx Mt S% R
669/22-669/20
669/3-669/13
P
32 18
14 62
40 20
14 3
70
0
Rpresiduals; S%ppercent solid substracted; Olpolivine;
Cpxpclinopyroxene; Plpplagioclase; Mtpmagnetite
Fig. 8 Trace element mass balance computed for steps A and B
according to a Rayleigh crystallization model. Shaded column
measured enrichment factor; open column calculated enrichment
factor. The good agreement between calculated and measured
data supports a fractional crystallization hypothesis to explain
both SET1 and SET2 trends
jor element mass balance results: The difference be-
tween calculated and measured enrichment factors
(ptrace element concentration in daughter rock/trace
elements concentration in parent rock) is less than 10%
for most of the elements, except for Ni, Rb and Sr
(Fig. 8). Even if this might also be related to the accura-
cy level of the analytical data and to incorrect distribu-
tion coefficients for these elements, the difference be-
tween measured and calculated values may be ac-
counted for by the lavas not being strictly representa-
tive of melts, due to the selective accumulation or sub-
traction of solid phases.
Eruptive dynamics
In principle, the evolution from earlier more primitive
to later more differentiated products during a parasitic
eruption with vents at low elevation might be inter-
preted as due to the gradual emptying of the central
feeding system filled with a compositionally zoned
magma. If this system is intercepted in its lowest part by
a fracture allowing the magma to rise up to the surface
at a low elevation, the deepest more primitive magma
will be poured out first, followed by the shallowest
more differentiated magma. This mechanism is, howev-
er, unreasonable for the 1669 eruption, because a con-
duit of unrealistic size would be required to be consis-
tent with the overall volume of erupted lavas (0.5–
1km
3
).
In our opinion, two points must be taken into ac-
count for interpreting the 1669 eruptive dynamics:
1. From a petrochemical and geochemical point of
view, the 1669 lavas define two quite different trends
(SET1 and SET2) with little evidence for transition-
al members.
2. SET1 lavas are erupted during the first stages of ac-
tivity and SET2 ones during the following ones.
These observations may be accounted for by assum-
ing a fractionated magma to reside within a reservoir
open to a high-level conduit system, where new deep
magma, more mafic but richer in volatiles, enters
through a tectonically induced fracture. Then the resid-
ing melt, although more acidic, is denser than the new
one, and a rapidly uprising laminar plume of the latter
may form in the reservoir (Sparks at al. 1980; Sparks
1983), eventually triggering eruptive activity because of
the increased pressure in the system (Blake 1981). The
plume melt would not significantly mix with the resid-
ing one and should be extruded first, preserving its ori-
ginal chemical features.
In the above model, SET1 rock compositions should
represent the uprising plume and SET2 the residing
more acidic magma (Fig. 9), which should be denser
than the more mafic buoyant plume.
Density calculation
The bulk density (
M
) of a crystal-bearing magma is
(Blake and Ivey 1986):
M
pj
X
c(1Pj)
L
, (1)
355
Fig. 9 Sketch of the proposed model. Relative dimensions of rep-
resented objects are not real
Table 3 Density values (kg/m
3
) measured at 25 7C and extrapo-
lated in the range 1000–1300 7C, by using literature volumetric ex-
pansion coefficients (Skinner 1966)
T (7C) Ol Cpx Pl Mt
25
1000
1100
1200
1300
3514
3404
3393
3383
3372
3370
3282
3277
3268
3259
2710
2667
2664
2660
2656
5750
4963
4946
4945
4904
where jpvolumetric proportion of phenocrysts (i.e.
porphyricity index);
X
pdensity of crystal assemblage
(p
S
[
i
7X
i
]), where
i
pdensity of i-mineral phase;
X
i
pvolumetric proportion of i-mineral); and
L
pden-
sity of the melt coexisting with the crystal assemblage.
This relation was applied to both SET1 (plume) and
SET2 (residing magma) lavas in order to estimate their
average densities. In order to simplify relative density
calculation, the effect of lithostatic pressure was ne-
glected because, reasonably, at the magma–plume in-
terface, this is the same for both magmas. However, we
did consider as relevant a possible temperature differ-
ence of the two magmas.
The crystal assemblage density was calculated in the
temperature range 1000–1300 7C by extrapolating the
volumetric expansion coefficients of olivine, plagio-
clase, clinopyroxene and magnetite, known in the range
100–1000 7C (Skinner 1966), to higher temperatures, so
that density of these minerals might be calculated for
appropriate magmatic conditions (Table 3), on the
grounds of the volume proportions of the phenocryst
phases of each of the sampled lavas for SET1 and
SET2. Average values of phenocryst volume propor-
tions and densities are given in Table 4A and B).
The melt density coexisting with the crystal assem-
blage was computed according to Bottinga and Weill
(1970), with partial molar oxide volumes by Lange and
Carmichael (1987, 1990) defined in the 1300–1600 7C
temperature range. Melt compositions for SET1 and
Table 4
A) Olivine, plagioclase, clinopyroxene and magnetite volumetric
proportions (%). Uncertainty is 1
s
SET 1
volume
proportion (%)
SET 2
volume
proportion (%)
Ol
Cpx
Pl
Mt
14B6
21B6
62B11
3B1
5B2
12B7
82B8
1B0.5
B) Average crystal assemblage densities (kg/m
3
) for both SET 1
and SET 2 in the temperature range 1000–13000 7C. Uncertainty
is 1
s
. Mean densities (and 1
s
) were obtained by averaging the
r
values of samples for the two SETS
T (7C) SET 1
r
(crystal
assemblage)
SET 2
r
(crystal
assemblage)
1000
1100
1200
1300
2720B21
2749B21
2711B20
2734B19
2678B22
2700B24
2672B20
2688B22
C) Average densities (kg/m
3
) for SET 1 and SET 2 magmas cal-
culated for different temperatures and volatile contents. Densities
are calculated according to Blake and Ivey (1986)
T (7C) SET 1 SET 2
r
L
(1%)
r
L
(2%)
r
L
(3%)
r
L
(1%)
r
L
(2%)
r
L
(3%)
1000
1100
1200
1300
2710
2697
2685
2672
2677
2665
2653
2641
2646
2634
2623
2611
2674
2663
2652
2641
2647
2637
2626
2615
2621
2611
2601
2591
SET2 on a dry basis were deduced by subtracting the
appropriate chemistry of phenocrysts, weighted accord-
ing to their modal proportions, from water-free whole-
rock compositions.
Values of
L
were then computed in the tempera-
ture range 1300–1600 7C for melts with 1, 2 and 3%
H
2
O contents, respectively, which are consistent with
experimental data for recent Etnean lavas (Metrich and
Clocchiatti 1989; Trigila et al. 1990). These
L
values
were extrapolated to the temperature range (1000–
1200 7C) for which crystal assemblage densities were
also calculated, and finally the average
M
values for
SET1 and SET2 were obtained by applying Eq. (1).
The average data show that if the SET2 magma, re-
siding in an open system, is cooler and volatile-depleted
with respect to the new uprising one (SET1), which ap-
pears to be a reasonable assumption, the latter is lighter
and may then diapirically ascend into the former.
For example, the data summarized in Fig. 10 show
that, if T
SET2
F1000 7C (consistent with its more acidic
nature and higher PI) and H
2
O
SET2
p1%, at
D
T
(SET1-
SET2)
p100 7C and
D
H
2
O
(SET1-SET2)
p1%, respectively,
D
(SET2-SET1)
equals 10 kg/m
3
; a plume may then rise
through the residing magma as, according to Sparks et
356
Fig. 10 Average density difference between residing magma and
plume
D
(SET2-SET1)
as a function of their difference in tempera-
ture
D
T
(SET1-SET2)
and
D
H
2
O
(SET1-SET2)
. We assume for the resid-
ing magma Tp1000 7C and volatile contentp1%
al. (1980),
D
p5 kg/m
3
is the minimum value to start a
basaltic plume by buoyancy into a reservoir. Any other
combination of
D
T and
D
H
2
O values resulting in
D
`5 kg/m
3
would allow the SET1 plume to rise. Ac-
cording to preliminary experimental work (Pompilio et
al. 1995) and computer simulation (Ghiorso et al. 1983)
at H
2
O
SET2
p1% and H
2
O
SET1
p2.5%, for tempera-
tures of, respectively, 10507 C (SET2) and 11007 C
(SET1) at P
tot
between 0.1 and 0.3 Gpa (which appear
reasonable for their overall chemistry and phenocrysts
content), a rising plume might form (Table 4C).
The plume type (Sparks 1983; Sparks et al. 1980)
may also be defined if one takes into account the lack
of transitional terms and structures suggesting mingling
processes. These observations are consistent with a
laminar flow regime of the plume (low Reynolds num-
ber) which causes it to rise through the residing magma
without any clear mixing processes. In these conditions
it is also possible to evaluate the plume ascent rate (v)
by the following equation:
vp(g
D
d
2
)/12 m, (2)
where gpgravity acceleration (p9.8 m/s
2
); mpresiding
magma viscosity (p103–104 Pa s); and dpfeeding con-
duit width (p3 m).
With
D
ranging from 5 to 50 kg/m
3
, the plume may
rise up through the magma residing in the reservoir,
with rates between 13 and 1300 m/h. These values are
clearly a rough estimate, because in Eq. (2) the effects
due to the irregular shape of the feeding fracture are
not considered, and also because both the plume and
residing magma should have a Bingham rheology due
to their temperature and proportion of suspended solid
phases. Besides, velocity values are reasonably high to
permit the plume to rapidly ascend toward the top of
the residing magma without mixing processes occurring
before the onset of the eruption itself.
Conclusions
Effusive temporal succession and petrochemical
data suggest that 1669 lavas group in two distinct SETS
which, on the whole, may not be referred to a fractional
crystallization process from a common parent magma.
Both rock sets have been interpreted as the result of
distinct fractional crystallization processes involving
slightly different primary magmas, which fractionate
different volumetric proportions of minerals; the con-
stant
87
Sr/
86
Sr values suggest that the source region of
both sets has a homogeneous isotopic character.
On the other hand, lavas of the two sets were
erupted during distinct stages. The first phases of activ-
ity were characterized by more mafic lavas (SET1),
whereas more acidic ones (SET2) were poured out dur-
ing the intermediate and final part of the eruption. This
sequence appears inverted with respect to what should
be expected by the magma rising up from a composi-
tionally zoned reservoir, and may not be accounted for
by emptying a zoned central conduit system, tapped at
depth by tensional fractures, because its volume is not
consistent with the volume (ca. 0.5–1 km
3
) of erupted
lavas.
It is then assumed that SET2 rock compositions
might represent a residing and fractionating magma
batch entered by new deep magma (SET1), through an
actively opening tensional fracture system. It is shown
that SET1 magma, although more mafic than SET2, if
hotter and richer in volatiles, is less dense and can con-
sequently rise through the reservoir as a buoyant plume
without mixing.
In the model defined above, a density difference of
approximately 10 kg/m
3
(
D
Tp100 7C and
D
H
2
Op1%)
is consistent with a computed uprise rate of the plume
around 25 m/h (under a laminar flow regime, with re-
siding melt viscosity of the order of 10
4
Pa s). That is
high enough to allow the residing batch to be crossed
without mixing with the new magma. This SET1 mag-
ma finally injected itself into the extensional fractures
developing up to the surface and fed the first eruptive
phases. Lavas derived from the uprising plume were
then poured out first, followed by the more acidic SET2
lavas from the residing batch, the ascent and eruption
of which were eventually triggered by the increased res-
ervoir pressure due to the new magma injection.
Evidence for the onset of the second eruption stage
is also given by the violent explosive activity of
25 March at the central crater, probably consequent to
a sudden pressure drop in the main conduit system, fol-
lowed by the collapse of the summit cone.
The proposed eruption model relates to a clear
change in the petrography of the lavas and dynamics at
Mount Etna, which occurred jointly with the 1669 erup-
tion. The plagioclase-rich SET2 lavas, similar to prod-
ucts of the earlier seventeenth century eruptions, are
representative of magma fractionating in a quite regul-
arly replenished magma reservoir. These quasi-steady
357
state conditions were upset by the input of volatile-rich
and hot magma from a slightly different source,
through a distinct fracture system, which induced the
1669 eruption, one of the largest Etna eruptions in his-
tory. The changes in the plumbing system and the ab-
normally high volume of the magma produced a signifi-
cant drop in the average eruption rate and difference of
style in the following decades (Mulargia et al. 1987; Ro-
mano and Sturiale 1982). Approximately ten flank
eruptions were recorded in the preceding century, since
1537, whereas only two occurred after 1669 until 1755.
Acknowledgements We express our thanks to Prof. A. Lo Giu-
dice, University of Catania, and to Prof. A. Peccerillo, University
of Calabria, for their helpful comments and constructive sugges-
tions on a previous version of the manuscript. We are grateful to
the reviewers (Drs. Batiza and Tanguy) for useful comments and
suggestions. We are also indebted to Prof. M. Barbieri, University
of Rome, for having made isotopic analysis possible at his facility,
and to Drs. F.Olmi and G. Vaggelli, Florence, CNR, Centro di
studio per la Minerogenesi e la Geochimica applicata, for their
assistance in the microprobe analysis. This research was carried
out with the financial support of the Ministry of University and
Scientific Technical Research (MURST, Rome) and from CNR
National Group of Volcanology (NGV, Rome).
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... The Valle del Bove (Figure 1b) volcanic succession is characterized by a rarity of primitive products and its prehistoric eruptions evolve up to trachyte encompassing high degrees of crystallization (>40%). This remarkable compositional variability has been attributed to crystal fractionation processes at shallow crustal levels mostly controlled by degassing and H 2 O exsolution phenomena [16,[22][23][24][25]. ...
... Major and trace elements of bulk rocks and single minerals have been analyzed for each rock sample and then discussed in the framework of magma modeling based on P-T-f O 2 -H 2 O-lattice strain equations. This approach constrains the crystallization and emplacement conditions of the sill, illustrating that the differentiation of prehistoric magmas started at intermediate (~6 km) depths [27][28][29][30] and proceeded through fractional crystallization, degassing and cooling phenomena at shallow crustal levels or during ascent towards the surface (e.g., References [16,24,25]). ...
... The Valle del Bove (Figure 1b) volcanic succession is characterized by a rarity of primitive products and its prehistoric eruptions evolve up to trachyte encompassing high degrees of crystallization (>40%). This remarkable compositional variability has been attributed to crystal fractionation processes at shallow crustal levels mostly controlled by degassing and H2O exsolution phenomena [16,[22][23][24][25]. ...
Article
Full-text available
This study documents the compositional variations of phenocrysts from a basaltic trachyandesitic sill emplaced in the Valle del Bove at Mt. Etna volcano (Sicily, Italy). The physicochemical conditions driving the crystallization and emplacement of the sill magma have been reconstructed by barometers, oxygen barometers, thermometers and hygrometers based on clinopyroxene, feldspar (plagioclase + K-feldspar) and titanomagnetite. Clinopyroxene is the liquidus phase, recording decompression and cooling paths decreasing from 200 to 0.1 MPa and from 1050 to 940 °C, respectively. Plagioclase and K-feldspar cosaturate the melt in a lower temperature interval of ~1000–870 °C. Cation exchanges in clinopyroxene (Mg-Fe) and feldspar (Ca-Na) indicate that magma ascent is accompanied by progressive H2O exsolution (up to ~2.2 wt. %) under more oxidizing conditions (up to ΔNNO + 0.5). Geospeedometric constraints provided by Ti–Al–Mg cation redistributions in titanomagnetite indicate that the travel time (up to 23 h) and ascent velocity of magma (up to 0.78 m/s) are consistent with those inferred for other eruptions at Mt. Etna. These kinetic effects are ascribed to a degassing-induced undercooling path caused principally by H2O loss at shallow crustal conditions. Rare earth element (REE) modeling based on the lattice strain theory supports the hypothesis that the sill magma formed from primitive basaltic compositions after clinopyroxene (≤41%) and plagioclase (≤12%) fractionation. Early formation of clinopyroxene at depth is the main controlling factor for the REE signature, whereas subsequent degassing at low pressure conditions enlarges the stability field of plagioclase causing trace element enrichments during eruption towards the surface.
... The basaltic trachyandesite (BT; MgO ≈ 4 wt.%) is representative of Etnean mugearites younger than the 16th century and erupted during the Recent Mongibello volcanic activity (Corsaro et al., 1996). With respect to the more differentiated products, the selected basaltic trachyandesite exhibits relatively low REE (La/Yb = 41) and HFSE (Zr/ Hf = 50) ratios, indicative of low degrees of crystal fractionation before eruption to the surface. ...
... For all the calculations, the most primitive hawaiitic rocks belonging to the 1669 AD eruption was assumed as the primitive magma (La = 63.1, Yb = 2.03, Zr = 216, and Hf = 4.5; sample 669D from Corsaro et al. (1996). The LKO eruptions are well reproduced by a two-step fractional crystallization mechanism, including clinopyroxene crystallization (13% for the FC1 vector) at the early stage of magma evolution, and subsequent plagioclase formation (22% for the FC2 vector). ...
... This discrepancy is resolved when FC calculations are reiterated using as starting composition one of the most primitive hawaiites (MgO ≈ 7 wt.%) of the 1669 AD eruption (La = 63.1, Yb = 2.03, Zr = 216, and Hf = 4.5; sample 669D from Corsaro et al., 1996). The petrographic features of some lavas emplaced before the voluminous 1669 AD event are also dominated by abundant (> 30%) and large (up to centimeter-sized) plagioclase crystals (Armienti et al., 1997;Armienti et al., 2004). ...
Article
The purpose of this review study is to reappraise in a more comprehensive form the thermodynamic principles behind the partitioning of trace elements between clinopyroxene and melt. The original corollary is that the partitioning energetics controlling the crystal-melt exchange are described by two distinct but complementary contributions: ΔGpartitioning = ΔGstrain + ΔGelectrostatic. ΔGstrain is the excess of strain energy quantifying the elastic response of the crystallographic site to insertion of trace cations with radius different from that of the major cation at the site. ΔGelectrostatic is the excess of electrostatic energy requiring that an electrostatic energy penalty is paid when a trace cation entering the lattice site without strain has charge different from that of the resident cation. Lattice strain and electrostatic parameters for different isovalent groups of cations hosting the same lattice site from literature have been discussed in comparison with new partitioning data measured between Tschermak-rich clinopyroxenes and a primitive phonotephritic melt assimilating variable amounts of carbonate material. Through such a comparatively approach, we illustrate that the type and number of trace cation substitutions are controlled by both charge-balanced and -imbalanced configurations taking place in the structural sites of Tschermak-rich clinopyroxenes. A virtue of this complementary relationship is that the control of melt composition on the partitioning of highly charged cations is almost entirely embodied in the crystal chemistry and structure, as long as these crystallochemical aspects are the direct expression of both ΔGstrain and ΔGelectrostatic. A size mismatch caused by cation substitution is accommodated by elastic strain in the surrounding lattice of clinopyroxene, whereas the charge mismatch is enabled via increasing amounts of charge-balancing Tschermak components, as well as the electrostatic work done on transferring the trace cations from melt to crystallographic sites, and vice versa. The influence of the melt chemistry on highly-charged (3+ and 4+) cation partitioning is greatly subordinate to the lattice strain and electrostatic energies of substitutions, in agreement with the thermodynamic premise that both these energetic quantities represent simple-activity composition models for the crystal phase. The various charge-balanced and -imbalanced configurations change principally with aluminium in tetrahedral coordination and the clinopyroxene volume change produced by heterovalent cation substitutions. In contrast, for low-charged (1+ and 2+) cations, the role of melt chemistry cannot be properly deconvoluted from the structural changes of the crystal lattice. The incorporation of these cations into the clinopyroxene lattice depends on the number of structural sites critically important to accommodating network-modifying cations in the melt structure, implying that the partitioning energetics of monovalent and divalent cations are strictly controlled by both crystal and melt properties. We conclude that the competition between charge-balanced and charge-imbalanced substitutions may selectively change the ability of trace elements to be compatible or incompatible in the clinopyroxene structure, with important ramifications for the modeling of natural igneous processes in crustal magma reservoirs which differentiate under closed- and open-system conditions.
... The basaltic trachyandesite (BT; MgO ≈ 4 wt.%) is representative of Etnean mugearites younger than the 16 th century and erupted during the Recent Mongibello volcanic activity (Corsaro and Cristofolini, 1996). With respect to the more differentiated products, the selected basaltic trachyandesite exhibits relatively low REE (La/Yb = 41) and HFSE (Zr/Hf = 50) ratios, indicative of low degrees of crystal fractionation before eruption to the surface. ...
... to 1886) lavas sampled on the SE flank of Mt. Etna volcano and emplaced during the Recent Mongibello activity (Corsaro and Cristofolini, 1996). These products were responsible for the construction of the summit cones by the emplacement of primitive to more evolved (MgO = 3-7 wt.%) lava flows with Na-affinity. ...
... The studied volcanic rocks share the common mineral association of Etnean magmas. Products earlier than the 16 th century are hawaiites and mugearites, whereas the younger lavas are hawaiites (Corsaro and Cristofolini, 1996). Bulk rock major and trace element concentrations, as well as Sr isotopes reveal that simple crystal fractionation is not responsible for the differentiation of magma (Corsaro and Cristofolini, 1996). ...
Preprint
A correct description and quantification of the geochemical behaviour of REE+Y (rare earth elements and Y) and HFSE (high field strength elements) is a key requirement for modelling petrological and volcanological aspects of magma dynamics. In this context, mafic alkaline magmas (MAM) are characterized by the ubiquitous stability of clinopyroxene from mantle depths to shallow crustal levels. On one hand, clinopyroxene incorporates REE+Y/HFSE at concentration levels that are much higher than those measured for olivine, plagioclase, and magnetite. On the other hand, the composition of clinopyroxene is highly sensitive to variations in pressure, temperature, and melt-water content, according to exchange-equilibria between jadeite and melt, and between jadeite/Ca-Tschermak and diopside-hedenbergite. As a consequence, the dependence of the partition coefficient on the physicochemical state of the system results in a variety of DREE+Y/DHFSE values that are sensitive to the magmatic conditions at which clinopyroxenes nucleate and grow. In order to better explore magma dynamics using clinopyroxene, a new P-T-H2O-lattice strain model specific to MAM compositions has been developed. The model combines a set of refined clinopyroxene-based barometric, thermometric and hygrometric equations with thermodynamically-derived expressions for the three lattice strain parameters, i.e., the strain-free partition coefficient (D0), the site radius (r0), and the effective elastic modulus (E).
... Etna. The lava flow inundated unusually distal locations, up to 20 km from the vent, and destroyed several villages along its path to the sea(Corsaro et al., 1996;Branca et al., 2013). The 1859 Mauna Loa lava flow, ∼ 51 km in length, inundated several fish ponds and strongly affected the local population at the time(Lipman and Banks, 1987). ...
... 4; e.g., Valentine and Connor, 2015).The 0.5 km 3 of lava erupted over a similar period as the 1669 CE eruption of Mt Etna (0.5 -1 km 3 , 122 days;Corsaro et al., 1996), the 1256 CE Madinah flow in Harrat Rahat volcanic field (0.44 -0.50 km 3 , 52 days;Camp and Roobol, 1989;Dietterich et al., 2018b) and the recent Fissure 8 eruption of Kīlauea volcano in 2018 (0.8 km 3 , 60 days; Neal et al., 2019).Peak effusion rates of Flow 1 are larger than most of the recent mafic eruptions but lower than those estimated during the rapid emplacement of the 1977 Nyiragongo lavas(Table 4.4;Komorowski et al., 2003). However, they compare well with peak effusion rates observed during the eruption of Mauna Loa in 1984 and Hekla in 1991(Gudmundsson et al., 1992;Lipman and Banks, 1987). ...
Thesis
Monogenetic volcanoes are the most common volcanic landforms on Earth and usually form isolated small-volume volcanic centres with a wide range of eruptive styles and products. Here, I focus on the case of Tseax volcano (Wil Ksi Baxhl Mihl) in north-western British Columbia, Canada's deadliest volcanic eruption; its ~ 1700 CE eruption killed up to 2,000 people of the Nisga'a First Nation. Tseax is composed by two imbricated volcanic edifices (an outer breached spatter rampart and an inner 70 m high tephra cone) and 4 far-travelled, valley-filling lava flows (2 pahoehoe and 2 'a'a) for a total volume of 0.5 km³ submerging the former Nisga'a villages. All the erupted products are Fe-, Ti-rich, basanite-to-trachybasalts and their geochemical homogeneity suggests the eruption of a single magma batch that was produced by low partial melting of a cpx-poor wehrlite at 52 - 66 km depth. The magma was stalled for > 10³ days in the upper crust and cooled down to 1094 - 1087 °C prior to eruption. The eruption lasted between 1 to 4 months and was divided in two main periods. The first period occurred in a typical Hawaiian-style with lava fountaining, spatter activity and the eruption of long pahoehoe flows. Almost half of the total lava volume was erupted in the first days of the eruption with fluxes > 800 m³/s. The lava may have engulfed the Nisga'a villages in a few tens of hours and thus be one of the cause for the fatalities. A "vog" produced when the lava entered the Nass River may have been also responsible for the Nisga'a deaths. The second period of activity was characterized by low intensity Strombolian explosions with the building of the tephra cone and eruption of the shorter 'a'a lava flows.In high speed channelised lava flows, standing waves are often interpreted as hydraulic jumps, indicating supercritical conditions. Using open channel hydraulic theory for supercritical flows, the geometry of the standing waves to constrain eruption flux and viscosity. I propose that investigating standing waves during ongoing eruption is a powerful tool to help for lava flow modelling and hazard mitigation.
... Etna. The lava flow inundated unusually distal locations, up to 20 km from the vent, and destroyed several villages along its path to the sea(Corsaro et al., 1996;Branca et al., 2013). The 1859 Mauna Loa lava flow, ∼ 51 km in length, inundated several fish ponds and strongly affected the local population at the time. ...
... of lava erupted over a similar period as the 1669 CE eruption of Mt Etna (0.5 -1 km 3 , 122 days;Corsaro et al., 1996), the 1256 CE Madinah flow in Harrat Rahat volcanic field (0.44 -0.50 km 3 , 52 days;Camp and Roobol, 1989;Dietterich et al., 2018b) and the recent Fissure 8 eruption of Kīlauea volcano in 2018 (0.8 km 3 , 60 days; Neal et al., 2019).Peak effusion rates of Flow 1 are larger than most of the recent mafic eruptions but lower than those estimated during the rapid emplacement of the 1977 Nyiragongo lavas ( ...
Thesis
Full-text available
Monogenetic volcanoes are the most common volcanic landforms on Earth and usually form isolated small-volume volcanic centres with a wide range of eruptive styles and products. Here, I focus on the case of Tseax volcano (Wil Ksi Baxhl Mihl) in north-western British Columbia, Canada’s deadliest volcanic eruption; its 1700 CE eruption killed up to 2,000 people of the Nisga’a First Nation. Tseax is composed by two imbricated volcanic edifices (an outer breached spatter rampart and an inner 70 m high tephra cone) and 4 far-travelled, valley-filling lava flows (2 pahoehoe and 2 ‘a‘a) for a total volume of 0.5 km3 submerging the former Nisga’a villages. All the erupted products are Fe-, Ti-rich, basanite-to-trachybasalts and their geochemical homogeneity suggests the eruption of a single magma batch that was produced by low partial melting of a cpx-poor wehrlite at 52 - 66 km depth. The magma was stalled for > 1000 days in the upper crust and cooled down to 1094 - 1087 degree Celsius prior to eruption. The eruption lasted between 1 to 4 months and was divided in two main periods. The first period occurred in a typical Hawaiian-style with lava fountaining, spatter activity and the eruption of long pahoehoe flows. Almost half of the total lava volume was erupted in the first days of the eruption with fluxes > 800 m3/s. The lava may have engulfed the Nisga’a villages in a few tens of hours and thus be one of the cause for the fatalities. A ‘vog’ produced when the lava entered the Nass River may have been also responsible for the Nisga’a deaths. The second period of activity was characterized by low intensity Strombolian explosions with the building of the tephra cone and eruption of the shorter ‘a‘a lava flows. In high speed channelised lava flows, standing waves are often interpreted as hydraulic jumps, indicating supercritical conditions. Using open channel hydraulic theory for supercritical flows, the geometry of the standing waves to constrain eruption flux and viscosity. I propose that investigating standing waves during ongoing eruption is a powerful tool to help for lava flow modelling and hazard mitigation.
... Tseax eruption rates also overlap with eruptions of similar volumes of tholeiitic lavas from large shield volcanoes. For example, eruption rates of 47-95, 116-174, 58, and 78-90 m 3 /s were estimated for the 1,669 Etna, 1859 Mauna Loa, 2018 Kilauea Fissure 8, and 2007 Piton de la Fournaise eruptions, respectively (Corsaro et al., 1996;Riker et al., 2009;Rhéty et al., 2017;Neal et al., 2019). The eruption of Tseax suggests that monogenetic eruptions can be comparable in size and time-averaged eruption rate to eruptions occurring on larger edifices with more complex plumbing systems and relatively stable magma storage zones. ...
Article
Full-text available
Despite having relatively short timespans of eruptions, monogenetic volcanoes can pose significant risks to the nearby population. Here, we describe the ~1700 CE eruption of Tseax volcano, British Columbia, which killed up to 2,000 people of the Nisga'a First Nation and is ranked as Canada's worst natural disaster. Within the Nisga'a culture, Adaawak stories preserve an observational account of the Tseax eruption. In this study, we establish the chronology of the eruption by integrating field observations and petrophysical data informed by Nisga'a oral and written histories. The Nisga'a stories corroborate the short duration and exceptional intensity of the eruption as recorded in the volcanic products. The eruption was divided in two main periods: 1) Period A and 2) Period B. 1) The eruption started in a typical Hawaiian style with low levels of lava fountaining that built up a spatter rampart. This pyroclastic edifice was breached by voluminous pāhoehoe lavas erupted at high discharge rates. We estimate that almost half of the emplaced lava volume (0.20 km 3) was erupted in Period A and had a flux of 800-1,000 m 3 /s. The low viscosity lava reached the Nass Valley, 20 km downstream of the volcano, in "swift currents", and engulfed the former Nisga'a villages in only 1-3 days, thus likely being responsible for the reported fatalities. The discharge rates progressively diminished to 10-200 m 3 /s until the end of this first eruptive period, which lasted a few weeks to a few hundred days. 2) The Period B eruption produced two 'a'ā lavas with discharge rates <50 m 3 /s. This period was also characterised by an explosive phase of eruption that built a 70 m high tephra cone overlapping with a spatter rampart; Period B lasted approximately 20 days. In total, the eruption produced 0.5 km 3 of volcanic materials (mostly in the form of lava flows) on the order of weeks to a few months. The mountainous terrain significantly controlled the emplacement of lava flows that reached long distances in a short amount of time. Our work shows that, under certain conditions, eruptions of small-volume monogenetic volcanoes ca pose risks comparable to flank eruptions on long-lived shield volcanoes.
... Of those which have occurred, it is the 1669 eruption which seems the most disastrous (Corsaro et al., 1996). As the well-known volcanologist Tazieff said, it was "an appalling calamity, when it seems the very cyclopes sitting in the interior of the mount rose" (Tazieff, 1978). ...
Article
Full-text available
This paper reports the first multidisciplinary petrologic, mineralogical, and geochemical studies of the near-crater tephra discharged by the 1669 catastrophic eruption of Etna stratovolcano, Sicily. We studied the grain-size distribution, chemical and mineral-phase composition of the tephra. We determined the composition of trace elements and the composition of encapsulated lithogenic gases. Etna is classified as an intraplate volcano with a deep-seated magma chamber. Of special importance is the fact that the Etnean products were found to contain volcanogenic organoids that have phase, elemental, and isotope compositions similar to the organoids encountered in diamond-bearing products discharged by some Kamchatka volcanoes. This corroborates out earlier inference that carbonaceous abiogenesis is ubiquitous in the conditions of onshore volcanism.
... Из уже случившихся наиболее катастрофичным по своим результатам представляется именно извержение 1669 г. [Corsaro et al., 1996]. По выражению известного вулканолога Г. Тазиева это был "чудовищный катаклизм, когда казалось, что поднялись сами циклопы, сидящие в недрах горы" [Тазиев, 1987]. ...
Article
Full-text available
Впервые проведены комплексные петролого-минералого-геохимические исследования прикратерной тефры катастрофического извержения в 1669 г. стратовулкана Этна на Сицилии. Исследованы гранулометрический, химический и минерально-фазовый состав тефры. Определено содержание в ней микроэлементов, состав капсулированных литогенных газов. Согласно полученным данным, Этна относится к внутриплитным вулканам с глубинным магматическим очагом. Особое значение имеет выявление в продуктах извержения Этны вулканогенных органоидов, близких по фазовому, элементному и изотопному составу органоидам в алмазосодержащих продуктах извержений некоторых камчатских вулканов. Это подтверждает ранее сделанный нами вывод о глобальном развитии углеродного абиогенеза в условиях наземного вулканизма.
Article
An understanding of destructive historic eruptions has important implications for the assessment of active plumbing systems and the processes that might precede future hazardous eruptions. At Mount Etna (Sicily, Italy), magma production and eruption frequency have increased dramatically since 1970, however, the recent eruptions are considerably less voluminous than those of the 17th century, which occurred at greater intervals. Seventeenth century activity culminated in the 1669 flank eruption, the most voluminous and destructive in Etna’s recorded history, marking the beginning of a new eruptive period. In this study, we examine trace element zoning patterns recorded in clinopyroxene (lava hosted microcrysts: 0·5–1 mm, lava hosted macrocrysts: 1–5 mm and scoria hosted megacrysts: >5 mm) to reconstruct magma dynamics leading up to the 1669 eruption. The clinopyroxene data are considered alongside previous studies of olivine and plagioclase to present an updated conceptual model for the plumbing system, providing a better understanding of magmatic processes in the lead up to hazardous volcanism. Petrological observations in combination with laser ablation ICP-MS mapping reveal sharp compositional zoning of clinopyroxene, not seen in major element transects. Trace element data, including Cr, Zr, Ni and rare earth elements, show that core, mantle and rim regions originated in distinct magmatic environments. Chromium-rich cores (up to 1080 ppm Cr) are in disequilibrium with the glassy-microcrystalline host groundmass and indicate crystal inheritance from a primitive magma source. Oscillatory zoning in the mantle of the crystals suggests a sustained period of magma replenishment and crystallization. Finally, ubiquitous Cr-rich (170–220 ppm) rims host many large melt inclusions, suggesting a final recharge event inducing relatively rapid crystal growth and eruption. Temperatures of 1120–1160 ± 27°C and pressures of 300–600 ± 200 MPa calculated for the three magmatic environments based on clinopyroxene composition at 2 wt % H2O place most of the clinopyroxene crystallization at more than 10 km depth. Measuring the consistent thickness of crystal rims (219 ± 33 µm) and assuming growth at a low degree of undercooling (10−8 cm/s), we calculate that the eruption triggering magma recharge invaded the plumbing system less than a month before eruption onset, in agreement with historical accounts of pre-eruptive seismicity. Notably, Cr enrichment in the recharge magma was not coupled with increases in MgO content. We therefore propose that a cryptic recharge with similar composition to the resident melt may have tipped the system to erupt, and that the volume of recharge rather than composition or temperature acted as the primary trigger. Finally, LA-ICP-MS maps of clinopyroxene from the previous eruption of Mount Etna (1651–53) revealed strikingly similar compositional zonation to that of 1669, supporting the notion that magmatic storage environments, associated with voluminous 17th century activity, were long-lived.
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The densities of 27 liquids in the system Na 2O-K 2O-MgO-MgO-FeO-Fe 2O 3-Al 2O 3-TiO 2-SiO 2 have been measured using the double-bob Archimedean technique. These results indicate that multicomponent silicate liquid volumes have a linear dependence on composition with the exception of the TiO 2 component. The equation: V(T) = ∑X i(T) overlineVi(T) + X Na 2O X TiO 2overlineVNa 2O -TiO 2 was used to derive values of the oxide partial molar volumes ( V¯i) by the method of least squares. Regressions were made separately at 1573, 1673, 1773 and 1873 K (as liquid ferric-ferrous ratios change with temperature) with relative standard errors for each fit of 0.38%, 0.32%, 0.30% and 0.32%, respectively. Derived d V¯i/dT values by separate least squares regression for each oxide component reproduce the measured dV/ dT of the experimental liquids by 20.21% on average. The effects of iron redox state on the density of a variety of natural liquids are demonstrated and at most amount to a variation of 1%. These new data on silicate liquid volumes were used to re-derive oxide partial molar compressibilities, d V¯i,T/dP and ´gb i T, at 1 bar from ultrasonic velocity and calorimetric data from the literature. The fits for d V¯i,T/dP and ´gb i,T at 1673 K have relative standard errors of 3.9% and 1.8%, respectively, which represent substantial improvements over previous fits. Two applications of these volume data are given: firstly, the fusion curve of diopside is calculated up to 95 kbr using an equation of state for liquid volume expressed as: V( T, P) = V( T) exp ∝ - β( T)(1 - bP+ cP2) dP (where β = K-1 and therefore dK/ dP = K' = - β-2dβ/ dP); secondly, using a range of K' appropriate to a komatiite liquid, the pressure-temperature conditions where the density of the liquid equals that of its olivine phenocrysts are calculated.
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This paper describes the use of pyroxene compounds of clinopiroxene in mafic and ultramafic rocks (inclusions and layered outcrops) in the Canary Islands as geobarometric indicators of the depth of formation of different rock types. The upper mantle origin of peridotite and gabbro inclusions was confirmed, while a crustal character is proposed for the layered complexes. Finally, a scheme of Canary substrate is outlined.
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The densities of 27 liquids in the system KâO-NaâO-CaO-MgO-FeO-FeâOâ-AlâOâ-TiOâ-SiOâ have been measured using the double-bob Archimedean technique. These results indicate that multicomponent silicate liquid volumes have a linear dependence on composition with the exception of the TiOâ component. Derived d{anti V}{sub i}/dT values by separate least squares regression for each oxide component reproduce the measured dV/dT of the experimental liquids by 20.21% on average. The effects of iron redox state on the density of a variety of natural liquids are demonstrated and at most amount to a variation of 1%. These new data on silicate liquid volumes were used to re-derive oxide partial molar compressibilities, d{anti V}{sub i,T}/dP and β{sub i,T}, at 1 bar from ultrasonic velocity and calorimetric data from the literature. The fits for d{anti V}{sub i,T}/dP and β{sub i,T} at 1673 K have relative standard errors of 3.9% and 1.8%, respectively, which represent substantial improvements over previous fits. Two applications of these volume data are given: firstly, the fusion curve of diopside is calculated up to 95 kbr using an equation of state for liquid volume, secondly, using a range of K' appropriate to a komatiite liquid, the pressure-temperature conditions where the density of the liquid equals that of its olivine phenocrysts are calculated.
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The recent and abrupt encounter of magma bodies with the phreatic system beneath the sedimentary basement of Mt. Etna is considered to be responsible for the alkali anomaly detected in lavas emitted since 1970. Geochemical work on the inclusions and the rocks of the sedimentary basement indicates that the Piedimonte and the Capo d'Orlando flysch units are the possible sources of contamination.