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ISSN 0145-8752, Moscow University Geology Bulletin, 2008, Vol. 63, No. 1, pp. 28–37. © Allerton Press, Inc., 2008.
Original Russian Text © Yu.V. Frolova, 2008, published in Vestnik Moskovskogo Universiteta. Geologiya, 2008, No. 1, pp. @–@.
Specific Features in the Composition, Structure, and Properties
of Volcaniclastic Rocks
Yu. V. Frolova
Received May 16, 2007
Abstract—The paper discusses patterns in the formation of composition, structure, and properties (physical
and physical–mechanical) of volcaniclastic rocks, which are rocks of specific origin occupying an intermediate
position between magmatic and sedimentary rocks. A database of volcaniclastic rocks, which contains geological, petrographic, and petrophysical information, has been created and analyzed. It has been shown that volcaniclastic rocks are a group that is extremely variable in its composition and properties, with rock properties
varying within a wide range. It has been found that the conditions of volcaniclastic rock formation and subsequent lithification are the principal geological factors that determine their properties. There are two different
origins of the properties of these rocks: (1) a long-term process of loose pyroclastic sediment lithification and
(2) immediate origination of solid rock because of the welding or baking of a sedimentary material. The following series of volcaniclastic rocks, organized by the degree of declining their physical and mechanical
parameters, has been reconstructed: clastic lavas
lava clastic rocks
ignimbrites
tuffs
hyaloclastites
agglutinates.
DOI: 10.3103/S0145875208010043
INTRODUCTION
Volcaniclastic rocks originate during volcanic eruptions in terrestrial, subaqueous, and subglacial environments and form rather diverse and complex rock
groups. They undergo subsequently compaction and
mineral transformations under the impacts of various
secondary processes, which result in a still greater
diversity of their composition, structure, texture, lithification degrees, and cementing types. The origin of volcaniclastic rocks is rather specific: they are intermediate between igneous (effusive) and sedimentary rocks.
Like effusive rocks, they originate during volcanic
eruptions and are similar in composition to effusive
rocks; however, they differ from them in their mode of
formation and, as a consequence, they also differ in
rock texture. Their clastic texture makes them similar to
sedimentary rocks, although the conditions of their sedimentation and subsequent lithification are different
from those of sedimentary rocks. These factors account
for difficulties in their examination and classification.
The characteristics of volcaniclastic rocks, i.e., the
description of their formation and transformation conditions under the action of secondary processes and
their classification and typification have been discussed
in detail in publications by volcanologists [Dzotsenidze
and Markhinin, 1974; Maleev, 1980; Petrografiya…,
2001] and lithologists [Strakhov. 1986; Frolov, 1995].
At the same time, this type of rocks has virtually not
been examined and described by professionals in soil
science. There are only individual papers discussing
properties of some types of volcaniclastic rocks in connection with some specific practical purposes. Generalizing publications consist only of O.A. Girina’s mono-
graph (1998), which discussed the formation conditions of loose andesite pyroclastic sediments in
Kamchatka in detail. This paper also presented their
composition, structure, and properties and suggested
their systematization. A publication by M.L. Bernard
(1999) presented a detailed description of volcaniclastic rocks from Mont Pelee volcano; it also analyzed
their density, elastic, thermal, and magnetic properties
and compared the results of laboratory and field geophysical studies.
General classifications of soils did not include volcaniclastic rocks for a long time [Gruntovedenie,
1983]. As well, tuffs, which are the most common varieties of volcaniclastic rocks, were included in the group
of effusive rocks, from which they are dramatically different in their mode of formation, structure, and properties. Modern classifications of grounds included volcaniclastic rocks as an independent subgroup for the
first time, both in the hard and soft rock groups (Gruntovedenie, 2005). This subgroup is termed as “volcanic–sedimentary” obviously after classifications by
lithologists [Frolov, 1995], whereas it is termed “volcaniclastic” in volcanologic classifications [Maleev,
1980; Petrografiya…, 2001], while volcanologists
apply the term “volcanic–sedimentary” to quite certain
rocks consisting of up to 50% of sedimentary material.
However, there are a number of debatable issues concerning the terminology and classification of volcaniclastic rocks. In particular, the issue of referring ignimbrites (welded tuffs) to magmatic or volcanic-sedimentary rocks remains debatable; the location of clastic
lavas in classifications is also ambiguous.
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SPECIFIC FEATURES IN THE COMPOSITION, STRUCTURE, AND PROPERTIES
A number of factors determined the need for examining the physical and mechanical properties of volcaniclastic rocks. Volcaniclastic rocks are widespread in
all tectonic settings, such as platforms, fold belts, and
island arcs; they make up a vast and very complex class
of rocks having their own specific features, and therefore they should be rightfully regarded along with magmatic, sedimentary, and metamorphic rocks. These
rocks are often foundations of various engineering
structures in regions of recent and ancient volcanism
and have to be dealt with during tunnel construction in
mountainous regions. Underground mine workings and
open pit mines are constructed in volcaniclastic rocks
because these rocks enclose various metals (iron, manganese, base metals, rare metals, gold, etc.) and nonmetal minerals (zeolite, bentonite, kaolin). Slag, tuffs,
and loose pyroclastic sediments are often applied as
construction materials, and this requires knowledge of
their properties [Produkty vulkanisma…, 1975; Gobanoglu et al., 2003; Ardau et al., 2004]. Volcaniclastic
rocks can form reservoir beds in petroleum fields, and
this calls for examining their reservoir properties. Beds
of volcaniclastic rocks were thoroughly examined during recent decades as they enclose accumulations of hot
water and steam [Ladygin et al., 2000]; and publications have appeared recently investigating volcaniclastic rocks as reservoirs for burial of radioactive wastes
[Avar et al., 2003]. One more reason for examining the
properties of volcaniclastic rocks is related to the problem of preserving geological and architectural memorials [Inaner et al., 2004].
A representative collection of volcaniclastic rocks
and a database (of approximately 700 specimens) were
collected at the Chair of Engineering and Ecologic
Geology of the Geological Faculty of the Moscow State
University. An analysis of the database provided the
possibility of examining the properties of volcaniclastic
rocks and finding their geological–engineering characteristics. It also allowed comparison of their different types
and revealing the principal geological and petrographic
factors that influence their properties and assess the role of
superimposed factors in the property formation.
In order to avoid inconsistencies in the terminology
and classifications of volcaniclastic rocks, the present
writer follows the classification recommended by the
Russian Petrographic Committee [Petrografiya…, 2001].
FACTUAL MATERIAL AND DATABASE
OF EXAMINED ROCKS
We made a representative collection of volcaniclastic rocks in the process of field studies during 1989–
1990 and 2001–2005, which were undertaken in Kamchatka, the Kuril Islands, the Siberian Platform, and in
Iceland. Field studies within Kamchatka were performed in the Pauzhetskii and Mutnovskii districts, on
the Bezymyannyi, Klyuchevskoi, and Avachinskii volcanoes, and on the Sredinnyi Range. Studies within the
territory of the Kuril Islands were undertaken on the
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Baranskii (Iturup Island) and Ebeko (Paramushir
Island) volcanoes; those within the Siberian Platform
were carried out in its northwestern portion (areas of
the Kharaelakh Basin and Vologochanskii Syneclise),
and those in Iceland were undertaken in its southern
and southwestern portions.
A database of volcaniclastic rocks including
approximately 700 specimens was created from the
results of the field and laboratory studies. The database
presents various types of rocks: rocks of different ages
(P–T, P –N1, N2–Q1, and Q), different textures (from
pelitic to psephitic), structures (massive and bedded),
and primary mineral composition (from silicic to
basic). The specimens demonstrated different epigenetic transformations (Kuril Islands: Iturup and Paramushir islands, age N2–Q; Pauzhetskii District in South
Kamchatka, age N2–Q); Iceland, age N2–Q; Norilsk
District in the Siberian Platform, age P2–T1) and local
hydrothermal lithogenesis (hydrothemal systems in the
Baranskii Volcano, Iturup Island; in the Ebeko Volcano,
Paramushir Island; and in the Mutnovskii, Paratunskii,
and Pauzhetskii hydrothermal systems in South Kamchatka). The database consists of the geological, petrographic, and petrophysical divisions.
The petrophysical division includes a set of physical
and mechanical parameters of the rocks, which were
either measured in the laboratory or calculated:
—density parameters include density (ρ), density of
the solid component (ρs), total porosity (n), effective
rock porosity to water (nt.wat) and to air (nt.air), and permeability (Kperm);
—moisture parameters include hygroscopic moisture (Wg) and water absorption value (W);
—acoustic parameters include the velocity of longitudinal wave propagation in dry (Vp) and water-saturated (Cpw) media, velocity of S-wave propagation (Vs),
coefficient (effect) of water saturation ( C V p ) showing
the percentage of changes in longitudinal wave propagation velocity upon water saturation of specimens;
—thermal parameters include heat conductivity (λ),
temperature conductivity (a), heat capacity (C), and the
anisotropy coefficient (Canis);
—magnetic parameters include magnetic susceptibility (ksi);
—deformation parameters include dynamic modulus of elasticity (Edyn) and Poisson’s ratio (mu);
—strength parameters include strength to uniaxial
compression of dry (Rc) and water-saturated (Rcw)
media, softening coefficient (Csoft), and breaking
strength (Rb).
All physical and mechanical parameters were determined according to standard procedures [Praktikum po
gruntovedeniyu, 1993]. We processed the data using
statistical software. The analysis of physical and
mechanical properties was accompanied by detailed
examination of the chemical and mineral composition
of the rocks, their texture and structure, and the morNo. 1
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30
FROLOVA
phology of their pore space; thus, we ensured an integrated approach to the rock investigation.
STUDY RESULTS: PETROPHYSICAL
CHARACTERISTICS
OF VOLCANICLASTIC ROCKS
The examined volcaniclastic rocks included clastic
lavas, lava clastites, tuffs and tuffites, hyaloclastites,
ignimbrites, and agglutinates. The table shows the
physical and physical–mechanical parameters of different types of volcaniclastic rocks.
Eruptive Clastic Rocks
Clastic lava is a rock consisting of lava fragments
cemented by a lava of other structure or composition. It
originates due to the cementing of solidified lava fragments formed by fragmentation of a lava flow in the
process of its flowing and inhomogeneous chilling.
According to E.F. Maleev’s (1980) data, both primary
lava and a secondary melt formed of fine clastic material due to secondary heating can cement these fragments. We examined clastic lavas in the Siberian Platform (Noril’sk District, P2–T1) and in Kamchatka (Klyuchevskii group of volcanoes, Q). The examined clastic
lavas are of basaltic composition, and this composition
provided for high values of the solid component density
(ρs = 2.85–2.98 g/cm3). Ancient clastic lavas in the
Siberian Platform underwent secondary transformations of their mineral composition under low-temperature regional metamorphism. These transformations
resulted in the first place in the formation of volcanic
glass in the pores and fissures of chlorite, zeolite, calcite, and chalcedony. Plagioclase crystals suffered partial replacement, while pyroxene crystals are virtually
fresh. No secondary alterations were found in clastic
lava collected in Kamchatka (Q): it consists of unaltered porous lava fragments. All the examined clastic
lavas are of a psephitic texture; the fragment size in all
specimens collected for laboratory examination does
not exceed 2–3 cm.
Clastic lavas are the densest and strongest rocks
among all the examined volcaniclastic rocks (table).
The porosity of ancient clastic lavas, whose pores are
filled with secondary minerals, does not exceed 12%,
and values within a 2–7% interval are preponderant.
The porosity of Quaternary clastic lava is 21%, which
formed at the expense of the porous texture of lava fragments. Closed pores dominate in the pore space
(nt.water/n < 0.5). The clastic lavas are not hygroscopic,
since their younger varieties do not include any secondary minerals, while the secondary minerals in ancient
clastic lavas do not contain any clay component.
The lava provenance of the lava fragments and
cement and the high density and low porosity of the
rocks caused their relatively high Vp values, and the
densest massive clastic lavas show the highest Vp values
(Vp > 5 km/s), which practically do not change with
water saturation ( C V p is approximately 0–5%). Low Vp
values are characteristic of fractured rocks in the dry
state (3.35–3.5 km/s), and the Vp values sharply
increase upon water saturation ( C V p increase to 50%).
Thus, fracturing of clastic lavas is a major negative factor similar to that in intrusive rocks, and this considerably decreases the strength and deformation properties
of clastic lavas. In addition, it increases the rock permeability, which is obvious from the high values of the
ratio between open and total porosity (not.por/n) reaching
0.87. Permeability growth, in turn, can give rise to
stronger transformation of rocks under the action of
secondary processes (hypergene, hydrothermal, and
metamorphic).
Lava clastic rocks originated upon disintegration of
lava flows with subsequent compaction and cementing
of formed detrital material during the process of lithogenesis. During subacqueous eruptions, lava fragments
can be cemented with roiled ooze or fine material
formed due to decomposition of the same lavas
(Maleev, 1980; Petrografiya…, 2001). A uniform composition and the texture and structure of fragments are
specific features of lava clastic rocks. We examined
lava clastic rocks from the area of the Mutnovskii volcano (South Kamchatka, N–Q). Their fragments consist of lava, though these fragments, contrary to clastic
lavas, are cemented with hydrochemical cement
formed during the lithification process. The lava clastic
rocks are somewhat less dense and strong as compared
to clastic lavas (table). Vp values vary in them within a
range of 3.9–5.4 km/s and do not change upon water
saturation, which indicates their massive structure and
lack of fracturing. The Rc values of the lava clastic
rocks vary from 33 to 158 MPa with preponderant values in the range of 80–100 MPa. Their high strength
values are due to the high density of lava fragments in
the lava clastic rocks. Most of these rocks are not-softening or weakly softening rocks (Csoft = 0.65–0.75 to
0.97); however, a conspicuous strength decline was
recorded in some cases upon water saturation (Csoft =
0.2–0.4). The composition of the cementing mass is the
principal factor determining the strength properties of
lava clastic rocks.
Hyaloclastites are vitroclastic rocks that originated
during subacqueous and subglacial eruptions as a result
of phreatic explosions, which are characterized by
eruptions of vitreous pyroclastic material. We examined hyaloclastites formed during subglacial eruptions
in the southern and southwestern areas of Iceland,
which were common during the Glaciation Epoch of
the Pliocene–Pleistocene. These rocks currently make
up thick successions and cover vast areas. The examined hyaloclastites consist of angular porous fragments
of basaltic volcanic glass ranging in size from psammite to small-grain psephite grain-size and more rarely
of olivine, pyroxene, and plagioclase crystal clasts.
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ρ, g/cm3
n, %
nt. water /n
Wg, %
Vp, km/s
KV p , %
Rc, MPa
Ksoft
χ × 10–3,
SI units
Clastic lavas
2.72 (8)*
-----------------------2.28–2.90
8 (8)
-----------2–21
0.45 (7)
-----------------------0.21–0.87
0.6 (7)
---------------0.3–1
4.4 (8)
--------------------3.35–5.6
12 (6)
-------------0–48
155 (7)
-----------------90–237
–
3.3 (8)
----------------0.3–12
Lava clastic
rocks
2.52 (38)
-----------------------2.32–2.66
8 (11)
-------------5–12
0.42 (4)
--------------------0.24–0.6
1 (11)
-----------------0.5–2.4
4.4 (39)
------------------3.9–5.4
– 1 (22)
-----------------–5 … 5
80 (30)
-----------------33–158
0.58 (13)
-----------------------0.21–0.97
–
Hyaloclastites
1.69 (74)
---------------------1.2–2.34
37 (63)
----------------14–57
0.7 (60)
-----------------------0.45–1.03
5.3 (62)
------------------0.6–13
1.85 (72)
---------------------0.9–4.05
35 (53)
-----------------------– 9 … 138
23 (61)
----------------2–110
–
1.4 (72)
------------------0.3–5.7
Tuffs
1.96 (493)
------------------------0.72–2.75
28 (392)
-------------------4.7–69
0.67 (377)
------------------------0.07–1.18
1.7 (397)
---------------------0–8.2
2.65 (490)
------------------------0.6–5.4
7 (447)
--------------------------– 41 … 275
42 (419)
-------------------1–200
0.61 (211)
------------------------0.1–1
8.3 (437)
---------------------0.05–65
1.61 (8)
--------------------1.36–2.2
45 (8)
--------------25–54
0.48 (7)
--------------------0.44–0.5
0.9 (2)
---------------0.8–1
2.15 (8)
-----------------------1.55–2.55
30 (7)
-------------0–55
10 (8)
-------------1–50
0.73 (7)
------------------0.38–1
11 (8)
-------------6–17
2.1 (8)
-----------------------1.71–2.34
20 (8)
--------------10–34
0.63 (8)
-----------------------0.49–0.74
0.1 (3)
3.5 (5)
--------------------1.75–4.5
10 (5)
--------------------– 1 … 39
73 (7)
-----------------48–102
0.85 (2)
-----------------------0.75–0.95
13 (6)
-------------7–33
Rock
Effusive
clastic
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Explosion
Agglutinates
clastic
Ignimbrites
SPECIFIC FEATURES IN THE COMPOSITION, STRUCTURE, AND PROPERTIES
MOSCOW UNIVERSITY GEOLOGY BULLETIN
Comparative property characteristics of various types of volcaniclastic rocks
Note: The numerator shows the average value of a parameter; in brackets – the number of determinations; the denominator shows the minimum and maximum values of the parameters.
31
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FROLOVA
(‡)
(b)
(c)
Fig. 1. Hyaloclastites (Southwestern Iceland, age Q3). Photomicrographs (parallel polarizers, field of view diameter
0.9 mm): (a) initial lithification stage; development of
palagonite cement at contacts between volcanic glass fragments; (b) film-type palagonite cement; (c) pore-type palagonite–smectite cement.
They are cemented with secondary minerals, among
which palagonite, smectite, zeolites, and chlorite are
the most common. The examined collection included
hyaloclastites of different ages (last Glaciation, Q3,
0.7–1.0 Ma, 1.7–2 Ma, and 2–2.5 Ma), and they underwent subsidence to different depths (no subsidence,
500 m, 700 m, and 1000 m). This allowed tracing and
revealing the patterns in the changes of their composition, structure, and properties due to lithogenesis processes [Frolova et al., 2004; Frolova et al., 2005].
Hyaloclastites are, overall, the most porous and least
dense rocks among volcaniclastic rocks (table),
although their properties largely depend on their lithification degree. Volcanic glass of basaltic composition is
the principal component of hyaloclastites and is a thermodynamically unstable material, which is readily
prone to transformations. It easily reacts with both cold
and thermal fluids, which results in chemical and mineralogical transformations and changes in the structure
of their pore space and permeability, as well as in the
gradual compaction and solidification of these rocks.
Palagonite is the first product of volcanic glass
transformation. Palagonitization is precisely the process that leads to cementing the loose pyroclastic sediments and forming solid rocks. An initial stage of
palagonitization was recorded in hyaloclastites formed
during the last glaciation (Q3), which remained on the
surface after their deposition and did not undergo any
subsidence. Palagonite forms, as if welded by fragments of volcanic glass at junction points that form
contact-type cement (Fig. 1a). Glass fragments remain
fresh in this case or change insignificantly at their
edges. These glass fragments become covered with
palagonite “coats,” forming a film-type cement at stronger palagonitization (Fig. 1b). The intergranular space
remains empty in this case. Palagonite also coats the
vesicle walls within glass fragments leaving their central parts empty. The palagonite coats gradually grow
and fill the intergranular space forming pore-type
cement (Fig. 1c). Palagonite subsequently transforms
into smectite, and vesicles in the glass become filled
with smectite.
Further transformations result in gradual smectite
transformation into mixed-layer minerals of a chlorite–
smectite series (corrensite) and in the formation of secondary minerals such as zeolites (chabazite, phillipsite,
and analcite) and calcite. Hyaloclastites 2–2.5 Ma old
that underwent subsidence to a depth of 1 km into hightemperature regions are the most transformed. Secondary transformations resulted in filling of the intergranular space, fractures, and pores with secondary minerals
including chlorite or corrensite, calcite, clinozoisite,
prehnite, epidote, and quartz, and volcanic glass
becomes considerably recrystallized, as opposed to the
previous stages, and replaced with secondary minerals.
Hyaloclastite lithification leads to regular and very
significant compaction and strengthening of the rocks
and to a decline in their porosity and permeability. Diagrams (Fig. 2) show changes in hyaloclastite properties
during their lithification. The n–Rc diagram distinctly
shows a porosity decline from 50–60% in weakly con-
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SPECIFIC FEATURES IN THE COMPOSITION, STRUCTURE, AND PROPERTIES
Rc, MPa
120
Vp, km/s
4.5
(a)
100
1
2
3
4
80
60
40
20
0
10
20
30
40
50
60
n, %
(c)
5000
4.0
3.5
3.0
1
2
3
4
2.5
2.0
1.5
1.0
0.5
1.0
1.2
(b)
1.4
ρs, g/cm3
3.0
Permeability, mD
500
2.9
50
5
2.8
1.6
1.8
2.0
2.2 2.4
ρ, g/cm3
(d)
2.7
0.5
2.6
0.05
0.005
0.0005
33
Average
1
2.5
Min–Max
2.4
2
3
4
Lithification degree
Average
1
± SD
2
3
4
Lithification degree
Fig. 2. Changes in hyaloclastite properties during lithification: (a) n–Rc diagram; (b) ρ–Vp diagram; (c) changes in permeability to
gas; (d) changes in solid phase density; (1) weakly lithified hyaloclastites that originated during the last Glaciation and are cemented
with contact–film-type palagonite cement; (2) hyaloclastites of Q3 age with pore-type palagonite–smectite cement; (3) hyaloclastites with pore-type cement of mixed composition (zeolite, corrensite, and calcite), 0.7–2 Ma old, subsidence depth of 500–700 m;
(4) lithified hyaloclastites, 2–2.5 Ma old, subsidence depth up to 1000 m.
solidated hyaloclastites with contact-type cement to
30–40% in hyaloclastites with pore-type smectite
cement and to 15–25% in rocks with porous cement of
mixed composition (zeolites, calcite, and corrensite)
(Fig. 2a). The strength of rocks consecutively grows in
this series. It was noted that the oldest hyaloclastites
show secondary porosity (n = 25–30%) due to transformation of the dense volcanic glass. This, however, did
not decrease the rock strength, which can reach a value
of 100 MPa due to formation of stronger structural
bonds in the process of rock lithification.
The ρ–Vp diagram shows a tendency toward the
growth of the Vp value due to hyaloclastite compaction
in the process of lithification (Fig. 2b). Zeolitized
hyaloclastites, which show lower Vp values, fall out of
the general ρ–Vp relation. Ladygin and his collegues
recorded and described a similar tendency earlier of
declining Vp values under the action of zeolitization in
Kamchatka tuffs [Ladygin et al., 2000]. We found upon
examination under an electron microscope that the zeolite matrix consists largely of the finest crystals measuring a few micrometers, which form secondary porosity.
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This presumably significantly attenuates the velocity of
elastic waves in the rock.
Investigation of hyaloclastites revealed a decline in
permeability by six orders of magnitude, depending on
the lithification degree, from 6 × 103 mD in weakly lithified hyaloclastites, which were formed during the last
Glaciation, to 0.001 mD in rocks, which originated 2–
2.5 Ma ago and underwent considerable consolidation
and cementing (Fig. 2c).
The diagram in Fig. 2d shows changes in the density
of the solid phase reflecting chemical transformations
that took place in the rock. ρs values decline regularly
during the initial stages of lithogenesis, which is caused
by gradual decomposition of volcanic glass and its
replacement with lighter minerals, including palagonite
(ρs = 1.93–2.14 g/cm3), zeolite (ρs = 2.2–2.3 g/cm3, and
smectite. Heavier secondary minerals crystallized
when the hyaloclastite succession subsided into a
region of higher temperature and pressure, which
resulted in the growth of the solid phase density.
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The hygroscopic moisture values depend largely on
the abundance of clay minerals, most of all smectite
and palagonite, and vary between 0.4 and 13%. Nonhygroscopic rocks include, first, weakly lithified hyaloclastites with extremely low abundance of clay minerals forming “bridges” between glass fragments
(Fig. 1a) and, second, most of the lithified Late
Pliocene hyaloclastites, where minerals of the smectite
series responsible for the hygroscopic properties of
rocks were transformed into chlorite.
Examination of the thermal parameters revealed values of conductivity coefficient varying between 0.4–0.5
and 0.8–1 Wt/(m · K) depending on the lithification
degree, which are anomalously low in volcanic rocks
[Popov et al., 2006].
EXPLOSIVE-CLASTIC LITHIFIED ROCKS
This rock group includes two subgroups: (1) lithified without cement: agglutinates (baked) and ignimbrites (welded) and (2) compacted and cemented with
hydrochemical cement, i.e., tuffs proper [Maleev, 1980;
Petrografiya…, 2001].
Ignimbrite is a rock consisting of clastic material
welded into a solid monolithic mass including lenticular bodies of volcanic glass. The glass is generally
deformed because of melting. Ignimbrites are confined
to areas of acid and, more rarely, intermediate volcanism and are not infrequently related to large collapse
calderas. Thick ignimbrite successions generally cover
vast areas up to several thousands and dozens of thousands of square kilometers. Ignimbrite successions are
known in Italy (Flegrea fields), Turkey (Anatolia), and
in New Zealand (the Taupo volcanic zone).
We examined ignimbrites from the Gorelyi volcano
in South Kamchatka (N–Q), which make up the foundation of the Mutnovskii Geothermal Power Plant.
These are rather compact, strong (Rc = 48–102 MPa),
nonhygroscopic rocks of low moisture capacity (W =
3–5%) (table). An oriented fluidal structure that is visible due to inclusions of volcanic glass in the form of
fiamme is a specific feature of ignimbrites. This causes
anisotropy of the elastic, strength, thermal, and permeability properties of ignimbrites, which have to be taken
into consideration during the calculation of the stability
of structure foundations.
Agglutinates are confined largely to areas of basaltic volcanism. Agglutinates, as opposed to ignimbrites,
are only locally distributed within cinder cones and in
the near-crater portions of volcanoes.
We collected and examined agglutinates (possibly,
pseudo-agglutinates, according to classification in
[Petrografiya…, 2001]) from the cinder cone at the
North Gap of the Bolshoy (Great) Fracture Tolbachik
Eruption (BFTE) (1975) and from the cinder cone at the
foot of the Kamen (Rock) volcano (Fig. 3a). The rock
consists of lava and scoria of variable porosity baked
into a homogeneous mass. The baking of fragments
(formation of connecting film) took place, obviously,
under the action of secondary heating and oxidation of
scoria material, which gave a reddish coloration to the
rock. Examination under an optical microscope
revealed the clastic texture of the agglutinates; a film
occurs around the lava and scoria fragments, which aids
baking and the formation of contact-type cement at
contact points between fragments (Fig. 3b).
The irregular form of the baked fragments causes
the high porosity of the rock (25–54%) (table). Open
porosity is generally half the total porosity. A lack of
clay minerals caused the low hygroscopic moisture
content (Wg < 1%). Vp values are low; however, they
conspicuously rise (by 30% as an average) due to the
filling of the voids with water. The agglutinate strength
changes from a few megapascals to 50 MPa depending
on the quantity and strength of the newly formed contacts.
Tuffs are rocks that originated due to compaction
and cementing of initially loose pyroclastic sediments
and that represent the most variable, complex, and
widespread group of volcaniclastic rocks. Thick tuff
successions occur virtually in all regions of recent and
ancient volcanism. We examined tuffs from the Kuril
Islands (N2–Q), Kamchatka ( P –N1, N2–Q, and Q), and
the Siberian Platform (P2–T1). The tuffs are very variable in their composition, structure and texture, and in
the character and intensity of their secondary alterations; they include pelitic, aleuritic, psammitic, and
psephitic varieties. There are lithoclastic, crystal-clastic, and vitroclastic varieties, as well as mixed types,
among them. Tuffs of different cement types occur:
contact, film, porous, and basal, and the cement composition is very variable: fine clastic vitreous, argillaceous, carbonate, quartzose, zeolitic, mixed, etc. The
total chemical composition of the examined tuffs varied
from rhyolitic and dacitic to basaltic. There are also
volcanic sedimentary rocks: tuffites enclosing an
admixture of sedimentary material up to 50% and
xenotuffs with an admixture of fragments from the volcanic basement.
The physical and mechanical properties of the tuffs
vary within wide limits (table) depending on the size
and composition of fragments, type and composition of
cement, and ratio between fragments and cement abundance. The tuff strength varies from a few megapascals
to 200 MPa, although it does not exceed 50 MPa in
most specimens. The properties of various tuffs change
differently upon water saturation. Rc values virtually do
not change in some specimens upon water saturation
and the rocks do not soften (Csoft = 1). The strength of
other specimens, particularly those enclosing clay minerals, considerably decreased upon water saturation
(Csoft = 0.1–0.2) and the tuffs soaked in some cases.
Generally, softening varieties are preponderant among
the tuffs (Csoft = 0.4–0.7).
Lithification degree is one of the main factors determining the properties of the tuffs, since the latter origi-
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SPECIFIC FEATURES IN THE COMPOSITION, STRUCTURE, AND PROPERTIES
35
(‡)
(b)
Fig. 3. Agglutinates: (a) cinder cone at the foot of the Kamen volcano, Kamchatka; (b) photomicrograph, clastic texture and baking
of clasts in the agglutinate from cinder cone (Northern Gap of BFTE, Kamchatka, 1975) (parallel polarizers, field of view diameter
0.9 mm).
nate due to gradual compaction of loose pyroclastic
sediments and their cementing during the lithogenesis
process.
DISCUSSION
The properties of volcaniclastic rocks originate in
different ways. Some volcaniclastic rocks become
cemented immediately upon their sedimentation
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Vol. 63
because of welding or baking of the clastic material.
These include clastic lavas, ignimbrites, and agglutinates. They are initially consolidated rocks, although
they may undergo subsequent compaction and lithification. Other volcaniclastic rocks (tuffs, hyaloclastites,
and lava clastic rocks) present initially loose clastic
material, which becomes compacted and cemented in
the process of lithogenesis, gradually turning into a
solid rock. In this case, thousands of years frequently
No. 1
2008
36
FROLOVA
ρ, g/cm3
3.0
(a)
Rc, MPa
Mean
± SD
(b)
200
2.5
150
4
2.0
100
1
50
1.5
clastic lavas ignimbrites hyaloclastites
agglutinates
lava clastic rocks tuffs
5
2
0
0
10
3
30
20
40
50
n, %
Rocks
Rc, MPa
150
Vp, km/s
6
(c)
coarse-psephitic tuffs
lava clastic rocks
5
(d)
coarse-psephitic tuffs
lava clastic rocks
4
100
3
50
2
0
1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
ρ, g/cm3
1
1.5
2.0
2.5
3.0
ρ, g/cm3
Fig. 4. Comparative property characteristics of various types of volcaniclastic rocks: (a) density; (b) n–Rc diagram; (1) tuffs;
(2) hyaloclastites; (3) lava clastic rocks; (4) clastic lava; (5) agglutinates; (c) ρ–Rc diagram of coarse-clastic tuffs and clastic lavas;
(d) ρ–Vp diagram of coarse-clastic tuffs and clastic lavas.
pass between sedimentation of loose clastic material
and the occurrence of solid rock.
lava clastic rocks resulted from higher density (lower
porosity) of their lava fragments.
Summarizing the obtained data on the properties of
volcaniclastic rocks, we constructed the following
series in order of their decreasing density, strength, and
deformational parameters and growth in their porosity:
clastic lavas, lava clastic rocks, ignimbrites, tuffs,
hyaloclastites, and agglutinates (table, Fig. 4a). However, this series is conditional, since the properties of
volcaniclastic rocks largely depend on their lithification
degree. Fig. 4b shows the dependence of strength to
uniaxial compression upon the porosity of various
types of volcaniclastic rocks: one can see that they follow the same pattern in tuffs, hyaloclastites, and agglutinates and that their curves virtually coincide. The
curve corresponding to clastic lavas lies conspicuously
higher. The clastic lava strength is higher by 40–
50 MPa than that of other volcaniclastic rocks at the
same porosity (density). This is due to the lava composition of the fragments and cement, providing stronger
structural bonds. The curve showing the strength of
lava clastic rocks is, conversely, located a little below
the common curve. The high strength values typical of
We compared two specimen groups, which are visually identical but are of different origins, with the purpose of determining the role of origin in the formation
of the properties of volcaniclastic rocks. We compared
lava clastic rocks and Paleogene–Neogene coarse-psephitic tuffs from the Kuril–Kamchatka Region. Rocks
in both groups consist of lava fragments 1–5 cm in size
cemented with material of hydrochemical origin. However, their formation conditions are different, as shown
above. The lava clastic rocks originated due to fragmentation of lava flows and the subsequent compaction
and cementing of the resultant clastic material during
lithogenesis. The clastic component consists of lava
lithoclasts of the same composition. The tuffs consist of
loose pyroclastic material formed during volcano
explosion. This material is more variable than that of
lava clastic rocks: it includes, as a rule, small-grained
clastic material consisting of crystal and volcanic glass
fragments in addition to lithoclasts of various composition and structure. The crystal and, particularly, the
glass clasts, are prone to decomposition, in contrast to
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SPECIFIC FEATURES IN THE COMPOSITION, STRUCTURE, AND PROPERTIES
CONCLUSIONS
(1) Volcaniclastic rocks make up a group of rocks
extremely variable in their composition and structures
with widely variable properties. The properties form in
different ways: in some cases, there is a continuous process of lithification of loose pyroclastic sediments and,
in other cases, a solid rock originates immediately due
to welding and baking of clastic material.
(2) The following series of volcaniclastic rocks has
been constructed in the order of decreasing values of
physical and mechanical properties: clastic lavas
lava clastic rocks
ignimbrites
tuffs
hyaloclastites
agglutinates.
(3) The formation conditions and the degree of subsequent lithification are the principal factors determining the petrophysical properties of volcaniclastic rocks.
Frolova, J., Ladygin, V., Franzson, H., et al., Petrophysical
Properties of Fresh to Mildly Altered Hyaloclastic Tuffs,
Proc. of WGC, Antalya, 24–29 April (CD ISBN 975–98332-0-4).
Frolova, Yu.V., Frenzson, Kh., Ladygin, V.M., et al., Porosity
and Permeability of Hyaloclastites, in Tr. Mezhdunarodnogo
geotermal’nogo nauchno-tekhnicheskogo seminara (Trans.
Intern. Geothermal Scientific–Technologic Conf.), Petropavlovsk-Kamchatski) (website http//ign2004.gesa.ru).
Girina, O.A., Piroklasticheskie otlozheniya sovremennykh
izverzhenii andezitovykh vulkanov Kamchatki i ikh inzhenerno-geologicheskie osobennosti (Pyroclastic Sediments
from Recent Eruptions of Andesitic Volcanoes in Kamchatka
and Their Geological–Engineering Specific Features), Vladivostok: Dal’nauka, 1998.
Gobanoglu, I., Yahya, O., and Ahmet, O., Engineering Properties of Tuffs in the Sandikli Region (Afyon–Turkey) and
Their Possible Use as Concrete Aggregates, Bull. Eng. Geol.
Env, 2003, vol. 62, pp. 369–378.
Gruntovedenie (Soil Science, 6th Edition), Trofimov, V.T,
Ed., Moscow: Mosk. Gos. Univ., 2005.
Gruntovedenie (Soil Science, 5th Edition), Sergeev, E.M,
Ed., Moscow: Mosk. Gos. Univ., 1983.
Inaner, H., Tokcaev, M., Kaya, T., et al., An Example of Geological, Geomorphological, and Cultural Heritage to Be Preserved: Kula (Katakekaumene) Volcanic Region in Western
Turkey, Proceed. of the 32nd International Geological Congress, Florence, August 20–28, 2004, Abstracts (Part 1), Florence, 2004, p. 625.
Ladygin, V., Frolova, J., and Rychagov, S., Formation of
Composition and Petrophysical Properties of Hydrothermally Altered Rocks in Geothermal Reservoir, in Proceed. of
the World Geothermal Congress, 2000, Tokyo, 2000,
pp. 2695–2699.
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research, project no. 07-05-00118-a.
Ladygin, V.M., Rychagov, S.N., Frolova, Yu.V., et al., Transformation of Loose Pyroclastic Rocks into Tuffs, Vulkanol.
Seismol., 2001, no. 4.
REFERENCES
Petrografiya i petrologiya magmaticheskikh, metamorficheskikh i metasomaticheskikh gornykh porod (Petrography
and Petrology of Magmatic, Metamorphic, and Metasomatic
Rocks), Popov, V.S, and Bogatikov, O.A.,, Eds., Moscow:
Logos, 2001.
Ardau, F., Argiolas, S., and Vernier, A., Technical Characterization and Main Uses of Sardinian Pyroclastic Rocks, Proceed. of the 32nd International Geological Congress, Florence, August 20–28, 2004, Abstracts (Part 1), Florence,
2004, p. 282.
Avar, B.B., Hudyma, N., and Karakouzian, M., Porosity
Dependence of the Elastic Modulus of Lithophysae-Rich
Tuffs: Numerical and Experimental Investigations, Intern. J.
of Rock Mechanics & Mining Scien., 2003, vol. 40, pp. 919–
928.
Bernard, M.L., Etude experimentale des proprietes physiques des roches pyroclastiques de la Montagne Pelee,
These, 1999.
Dzotsenidze, G.S. and Markhinin, E.K., Volcaniclastic sediments and the Problem of Their Evolution, in Problemy vulkanogenno-osadochnogo litogeneza (Problems of Volcanic–
Sedimentary Lithogenesis), Moscow, 1974.
Frolov, V.T., Litologiya (Lithology), Moscow: Mosk. Gos.
Univ., 1995, vol. 2.
MOSCOW UNIVERSITY GEOLOGY BULLETIN
Vol. 63
Maleev, E.F., Vulkanity: Spravochnik (Volcanic Rocks: Reference Book), Moscow: Nedra, 1980.
Popov, V.G., Petrunin, G.I., Pugina, L.M., et al., Influence of
Consolidation (Lithification) Degree on Heat-Transfer
Parameters of Tuffs (a Case History of Iceland Tuffs), in Tez.
dokl. Vos’mykh geofizicheskikh chtenii im. V.V. Fedynskogo
(2–4 marta 2006 g.) (Abstracts of Papers of the Eighth Geophysical Readings (March 2–4, 2006)), Moscow, 2006,
pp. 88–89.
Praktikum po gruntovedeniyu (Practical Training in Soil Science), Trofimov, V.T, and Korolev, V.A, Eds., Moscow:
Mosk. Gos. Univ., 1993.
Produkty vulkanizma kak poleznye iskopaemye (Volanic
Rocks as Mineral Products), Moscow: Nauka, 1975.
Strakhov, N.M., Osnovy teorii litogeneza (Fundamentals of
Lithogenesis Theory), Moscow: Nauka, 1960.
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lava fragments, under the action of epigenetic processes
and to replacement with secondary minerals forming a
rather strong cementing mass. These specific features
in the rock origin determined the petrophysical differences between coarse-psephitic tuffs and lava clastic
rocks. The ρ–Rc and ρ–Vp diagrams (Figs. 4c and 4d)
show that the relative petrophysical homogeneity of
lava clastic rocks (as a consequence of their petrographic homogeneity) is their distinguishing feature.
The tuffs are, conversely, extremely inhomogeneous in
their properties: their density, strength, and Vp values
change within wide limits. In addition, the coarse–psephitic tuffs are generally somewhat stronger than the
lava clastic rocks, even at equal density (porosity).
37