Eos, Vol. 69, No. 42, October 18, 1988
years o r d e c a d e s . W h e n m o d e l s a r e calibrat­
e d , it g e n e r a l l y is a s s u m e d t h a t t h e a q u i f e r
system is in a n a t u r a l s t e a d y state c o n d i t i o n
prior to h u m a n influence. Papers presented
d u r i n g this s y m p o s i u m d e m o n s t r a t e t h e falla­
cy of this a s s u m p t i o n in m a n y situations.
M a n y o f t h e talks s h o w e d t h a t g r o u n d w a t e r
flow systems c a n c h a n g e d y n a m i c a l l y o v e r
geologic t i m e in r e s p o n s e t o c h a n g i n g b o u n d ­
ary c o n d i t i o n s , h y d r a u l i c stresses, o r a q u i f e r
p r o p e r t i e s . S u c h c h a n g e s c a n b e c a u s e d by
l o n g - t e r m climatic c h a n g e s , sea level c h a n g e s ,
glacial l o a d i n g o r u n l o a d i n g , t e c t o n i c forces,
m i n e r a l dissolution o r p r e c i p i t a t i o n , a n d d e ­
position o r e r o s i o n o f s e d i m e n t s . E a c h of
t h e s e processes was a d d r e s s e d by o n e o r
more speakers.
P e r h a p s t h e single m o s t i m p o r t a n t a n d p e r ­
vasive t h e m e was t h a t m o d e r n g r o u n d w a t e r
systems m a y still b e u n d e r g o i n g slow t r a n ­
sient r e s p o n s e s to c h a n g e s in stresses t h a t
now a p p e a r constant o r to processes that a r e
n o l o n g e r active. T h i s m a y b e m a n i f e s t e d by
a n o m a l o u s h y d r a u l i c h e a d s o r by inconsisten­
cies b e t w e e n m o d e r n h y d r a u l i c g r a d i e n t s a n d
t h e d i s t r i b u t i o n s of solutes, i s o t o p e s , o r t e m ­
p e r a t u r e . F o r e x a m p l e , several p a p e r s
s h o w e d t h a t t h e p r e s e n t p o s i t i o n o f t h e fresh­
water-saltwater i n t e r f a c e ( o r t r a n s i t i o n z o n e )
in coastal a q u i f e r s o n b o t h th% /3tlantic a n d
Pacific coasts of t h e U n i t e d States a r e n o t
n o w in e q u i l i b r i u m with sea level. F r e s h w a t e r
extends farther offshore t h a n can be ex­
p l a i n e d by p r e s e n t - d a y sea level, a n d t h e in­
terface reflects a l o n g - t e r m a v e r a g e sea level
at a b o u t 1 5 - 3 0 m l o w e r t h a n p r e s e n t . C o n s e ­
q u e n t l y , t h e i n t e r f a c e is m i g r a t i n g n a t u r a l l y
toward the land. This type of natural tran­
sient c h a n g e m u s t b e r e c o g n i z e d a n d differ­
e n t i a t e d f r o m artificially i n d u c e d effects if ac­
c u r a t e p r e d i c t i o n s of f u t u r e c h a n g e s in
g r o u n d w a t e r flow a n d quality a r e t o b e m a d e .
Several p a p e r s f o c u s e d o n t h e w e s t e r n
U n i t e d States, w h e r e geologically r e c e n t cli­
matic c h a n g e s h a v e a l t e r e d r e c h a r g e p a t t e r n s
to aquifers. T h e c h a n g e in r e c h a r g e , in t u r n ,
causes c h a n g e s in t h e flow systems, w h i c h
t h e n affect w a t e r quality. O t h e r p a p e r s dis­
cussed l o n g e r - t e r m geological p r o c e s s e s relat­
e d to s e d i m e n t a t i o n a n d e r o s i o n . E r o s i o n a l
unloading a n d topographic changes can have
s t r o n g influences o n g r o u n d w a t e r flow pat­
t e r n s in l o w - p e r m e a b i l i t y e n v i r o n m e n t s .
T h e r e , significant u n d e r p r e s s u r i n g is c a u s e d
by a d j u s t m e n t t i m e s o n t h e o r d e r o f several
millions o f y e a r s . C o n v e r s e l y , h i g h d e p o s i tional r a t e s a n d s e d i m e n t c o m p a c t i o n , s u c h as
o c c u r s in t h e G u l f C o a s t b a s i n , c a n l e a d t o
significant o v e r p r e s s u r i n g . I n c e r t a i n cases, it
m i g h t b e possible f o r a h i g h - t e m p e r a t u r e b a ­
salt i n t r u s i o n t o i n d u c e p r e s s u r e a n o m a l i e s in
sediments that a r e retained for t h o u s a n d s of
years after t h e i n t r u s i o n ' s h e a t h a s d i s s i p a t e d .
Some of t h e other p a p e r s noted t h e potential­
ly i m p o r t a n t r o l e o f g r o u n d w a t e r flow in c o n ­
trolling t h e m i g r a t i o n a n d a c c u m u l a t i o n o f
oil. U n d e r s t a n d i n g t h e e v o l u t i o n o f g r o u n d ­
w a t e r flow t h r o u g h p e t r o l e u m s o u r c e b e d s
a n d t r a p s c a n l e a d t o i m p r o v e m e n t s in e x p l o ­
ration a n d d e v e l o p m e n t strategies.
A c o m m o n feature a m o n g most of t h e re­
p o r t e d s t u d i e s was t h e u s e o f n u m e r i c a l s i m u ­
lation m o d e l s t o aid in analysis. G r o u n d w a t e r
flow, s o l u t e - t r a n s p o r t , a n d h e a t - t r a n s p o r t
m o d e l s w e r e consistently u s e d t o s i m u l a t e
processes o v e r p e r i o d s o f t h o u s a n d s o f y e a r s
to millions o f y e a r s .
In summary, the papers demonstrated that
u n d e r s t a n d i n g l o n g - t e r m climatic a n d g e o l o g ­
ic processes c a n a i d in t h e analysis o f g r o u n d ­
w a t e r flow systems a n d h e l p e x p l a i n o b s e r v e d
a n o m a l i e s in h e a d a n d w a t e r quality. C o n ­
versely, a k n o w l e d g e a n d u n d e r s t a n d i n g o f
the dynamics a n d evolution of g r o u n d w a t e r
flow systems m a y h e l p i n e x p l a i n i n g o r i n t e r ­
p r e t i n g c e r t a i n geologic f e a t u r e s a n d p r o c e s s ­
es, s u c h as d i a g e n e s i s , o r e d e p o s i t i o n , p e r m e ­
ability, a n d p o r o s i t y e n h a n c e m e n t , a n d p e t r o ­
leum migration.
This report was contributed by Leonard F. Konikow, U.S. Geological Survey, Reston, Va. and
Donald I. Siegel, Department of Geology, Syracuse
University, Syracuse, N.Y.
Elements, Oxides,
Silicates: High Pressure
Phases With Implications
for the Earth's Interior
d i a g r a m s t o t h e r m o d y n a m i c p r o p e r t i e s . Crys­
tal c h e m i c a l p r i n c i p l e s a r e s u m m a r i z e d , as
well as t h e m a i n f e a t u r e s of t h e t e c h n i q u e s
and apparatus employed to obtain the data
s u m m a r i z e d in t h e r e m a i n d e r o f t h e b o o k .
A l t h o u g h r e f e r e n c e s to a p p a r a t u s p a p e r s a r e
n u m e r o u s a n d well c h o s e n , r e f e r e n c e s to
w o r k s which r e l a t e t h e r m o d y n a m i c p r o p e r t i e s
to c o n t r u c t i o n o f p h a s e d i a g r a m s a r e lacking.
T a b l e 1.3, a s u m m a r y of t h e ionic r a d i i of el­
e m e n t s in d i f f e r e n t c o o r d i n a t i o n s a p p e a r s to
m e to b e t h e m o s t v a l u a b l e p a r t of C h a p t e r 1.
C h a p t e r s 2, 3 , a n d 4 , in w h i c h t h e p h a s e di­
a g r a m of t h e e l e m e n t s , p x i d e s , a n d silicates
a r e s u m m a r i z e d , a r e t h e h e a r t of this b o o k .
T h e p r e s s u r e r a n g e c o v e r e d varies f r o m 4 0
to 5 0 k b a r f o r m a t e r i a l s w h o s e p h a s e dia­
g r a m s w e r e s t u d i e d with a p i s t o n c y l i n d e r a p ­
p a r a t u s a n d u p t o 3 0 0 0 k b a r for t h e case of
i r o n w h i c h h a s b e e n s t u d i e u s i n g s h o c k wave
t e c h n i q u e s . Similarly, t h e t e m p e r a t u r e r a n g e s
of t h e p h a s e d i a g r a m s v a r y f r o m ~ 1 0 K to
10 K, d e p e n d i n g on the range over which
the melting point has been explored. T h e
crystal s t r u c t u r e s o f m o s t of t h e solid poly­
m o r p h i c p h a s e s a r e r e p o r t e d o n t h e basis of
in situ a n d q u e n c h e d X r a y diffraction m e a ­
s u r e m e n t s c o n d u c t e d in m u l t i a n v i l a n d dia­
m o n d anvil p r e s s u r e a p p a r a t u s d u r i n g t h e
last 2 0 years.
I n g e n e r a l , t h e h u g e task o f c o m p i l i n g a n d
critically r e v i e w i n g p h a s e e q u i l i b r i u m d a t a
for h u n d r e d s of m a t e r i a l s h a s b e e n c a r r i e d
o u t e x t r e m e l y well. I n t e r s p e r s e d w i t h p h a s e
d i a g r a m s a r e s o m e useful tables a n d figures
p r o v i d i n g c r y s t a l l o g r a p h i c d a t a for g r o u p s of
c o m p o u n d s a n d d e m o n s t r a t i n g t h e systematics of m o l a r v o l u m e v e r s u s c a t i o n - a n i o n dis­
t a n c e for r e l a t e d c o m p o u n d s a n d s t r u c t u r e s .
A technical flaw in t h e b o o k , w h i c h is easily
c o r r e c t e d , is a missing p h a s e d i a g r a m for
P b C r 0 (p. 143). U n f o r t u n a t e l y , t h e c a p t i o n is
n o t missing a n d , as a result, t h e n e x t 5 1
phase diagms have the wrong caption. This
p r o b l e m is n o t s o r t e d o u t u n t i l p p . 178 a n d
179, w h e r e t h e p h a s e d i a g r a m of K C r 0 is
given twice (on p . 179 with t h e c o r r e c t c a p ­
tion).
I n discussing successive p h a s e t r a n s f o r m a ­
tion of t h e silicates with p r e s s u r e ( e i t h e r in
C h a p t e r 4 o r 5) it w o u l d h a v e b e e n h e l p f u l to
t h e r e a d e r t o h a v e p r o v i d e d a d e t a i l e d series
of o b s e r v e d a n d / o r t h e o r e t i c a l seismic velocity
v e r s u s d e p t h profiles for t h e t r a n s i t i o n r e g i o n
of t h e E a r t h . T h e r e l a t i o n o f s h a r p seismic
velocity increases to p h a s e t r a n s f o r m a t i o n in
t h e 2 0 0 - to 7 0 0 - k m - d e p t h r a n g e o f t h e E a r t h
a r e extensively d i s c u s s e d in C h a p t e r 5. Also
in C h a p t e r 5, several d e t a i l e d m a n t l e m o d e l
c o m p o s i t i o n s a r e given in a series of tables.
T h e i r significance w o u l d b e e a s i e r t o c o m p r e ­
h e n d if t h e tables specifying t h e s e ( 5 . 1 - 5 . 1 0 )
h a d c a p t i o n s . A s u m m a r y of c o s m o c h e m i c a l
c o n s t r a i n t s a n d t h e r e l a t i o n of m a n t l e m o d e l s
to t h e o b s e r v e d c h e m i s t r y o f c r u s t a l r o c k s d e ­
rived f r o m p a r t i a l m e l t p r o c e s s e s w o u l d h a v e
m a d e this last c h a p t e r m o r e c o m p l e t e .
I n spite o f t h e m i n o r deficiencies in t h e
p r e s e n t p r i n t i n g , this m o n u m e n t a l w o r k is a
highly useful a n d l o n g - n e e d e d b o o k w h i c h
will serve solid E a r t h scientists for m a n y
years.
2
PAGE 9 6 4
L i n - g u n Liu a n d William A. Bassett, O x f o r d
University Press, N e w Y o r k , xi + 2 5 0 p p . ,
1986, $ 4 9 . 9 5 .
Reviewed by Thomas J. Ahrens
A vitally i m p o r t a n t a s p e c t of u n d e r s t a n d i n g
t h e c o m p o s i t i o n , s t r u c t u r e , a n d p r o c e s s e s act­
i n g within t h e solid E a r t h is o b t a i n i n g a c o m ­
plete as possible k n o w l e d g e of t h e fields of
stability o f t h e E a r t h ' s c o m p o n e n t m i n e r a l s
a n d t h e i r h i g h - p r e s s u r e p o l y m o r p h s with r e ­
spect t o p r e s s u r e a n d t e m p e r a t u r e . L i u a n d
Bassett's b o o k is t h e first effort w h i c h h a s fo­
c u s e d o n b r i n g i n g t o g e t h e r t h e available
p h a s e d i a g r a m s for t h e e l e m e n t s , o x i d e s , a n d
silicates t h a t a r e r e l e v a n t t o t h e u n d e r s t a n d ­
ing of Earth's a n d t h e o t h e r terrestrial plane­
tary i n t e r i o r s . Since t h e b o o k also covers t h e
elements a n d c o m p o u n d s important to the
shallow r e g i o n of t h e m a n t l e s o f t h e m a j o r
p l a n e t s (e.g., H , H e , C, a n d H 0 ) , it is a n in­
valuable s o u r c e of d a t a for scientists s t u d y i n g
t h e i n t e r i o r s of t h e s e p l a n e t s as well.
A n initial i n t r o d u c t o r y c h a p t e r lays o u t , in
very c o n d e n s e d f o r m , t h e r e l a t i o n of p h a s e
2
2
2 o
3o
This page may be freely copied.
3
2
2
7
Thomas J. Ahrens is with the Seismological Lab­
oratory, California Institute of Technology, Pasa­
dena, Calif.