ML19323G563
| ML19323G563 | |
| Person / Time | |
|---|---|
| Issue date: | 04/03/1980 |
| From: | Lefevre H Office of Nuclear Reactor Regulation |
| To: | Rolonda Jackson Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8006040443 | |
| Download: ML19323G563 (4) | |
Text
.
4,
\\
W I
I 4
{
APR.31980 l
s MEMORANDUM FOR:
Robert E. Jackson, Chief Geosciences Branch, DSS t
FROM:
Harold E. Lefevre, Geologist i
Geology and Seismology Section Geosciences Branch, DSS i
SUBJECT:
ERUPTION OF MOUNT ST. HELENS, A CASCADE VOLCANO IN SOUTHWESTER!i WASHINGTON STATE i
(
Early Thursday afternoon, March 27, 1980, Mount St. Helens, a Cascade volcano inactive since 1857 erupted and emitted a small amount of ash. The volcano is located in s'outhwestern Washington state approximately 35 miles northeast-of the Trojan Nuclear Power Plant (see attached location map). Physic'al evidence of volcanic activity was preceded by a series of moderate earthquakes of Richter Magnitude'4.0 and less beginning.on Thursday, March 20, 1980. *Bolcanic activity l.
(ash-la. den steam principally) has continued intermittently since that time.
As of today (April 1, 1980) ash has been reported at distances ranging from 30 miles east to 90 miles southeast oftthe volcano. There have been scattered, j
unconfimed reports of some ash at Portland, Oregon,.some 45 miles south of 'Hount St'. Helens. With the exception of a trace near the volcano summit no ash fall has been reported either to the west or to the southwest. The preceding
. information as well as the following has been gathered from a variety of sources including (1) the U. S. Geological Survey (2) geologists from the states of Oregon and Washington (3) the University of-Washington and (4) the U. S. Forest Service.
Pertinent information' includes: -
i 1.. Subsequent to a Magnitude.4.0 (Richter) event on Thursday, March 20 seismic activity in the Mount St. Helens area has increased rapidly.
i 2.
At least two events per hour were recorded early in-the sequence (Thursday,-
March 20 through early Monday, March 24). By Monday noon an average of -
l 40-50 events per hour were occurring. Between 3PM and 4PM on Tuesday, March 25 from three to four Magnitude 4.0 or so events per hour were occurring, by 4PM, EST Wednesday the frequency of Magnitude 4.0's had j
dropped to pre-Tuesday afternoon levels. However, the number of t!agnitude 3.0's and less has increased dramatically such that the events could not l
be distinguished'- At 4PM, Thursday, March 27, 6 to 7 events per hour of_
~
g'[
Magnitude 3.0 were being recorded. The'two largest events, as reported by Aj i
i k~
/
OF F BC. >
,7,,,,,,,,,,,,*,
...g. g.q.3..........
_e_.>
........m......
! IWC 50RM 318 (9 76) NRCM 0240 it u.s.. eve==esear eneavine e Ficu s e ese. es e. es.
,.......:. A 1
~.
3...
~
gn W
APR m
Y a
gy%
K 2 :-
~
j the University of Washington, are of Magnitude 4.7.
Gae occurred Monday e
evening, March 31; the other on April 1.at 4:23 AM. Magnitude 3.0's and l
greater are now occurring at a rate 'of-2-to 3 per hour. Events of less than Magnitude 3.0 aie decreasing.
t l
3.
Seismic activity seems confined to an area beneath and northwest of the summit with focal depths ranging from 1km to as much as 10 km. _The i
deeper events are'quite rare.
~
i 4
By Tuesday noon (April 1) 12 seismic instruments were at th6 site (1 permanent,
~
114 portable). The monitoring is being conducted by Dr. Steve Malone and Dr'. Robert.Crosson'of the1 University of Washington and by-Dr. Craig i
Weaver of the U. S. Geological Survey.
5.
The earthquakes (even the larger' events) are felt only locally and then only 1
. if the observer is motionless. Groundmot'
.) apparently cannot be detected if the observer ~is-in a moving car. flone have been either felt or recorded at the Trojan plant. The threshold of the on-site instruments (at least.
l 12 internal and free-field) is 0.01g. All these instruments are operative s
and have.been recently calibrated.
6.
In ' addition to venting (steam vapor and ash) other effects of the Mount j
St. Helens volcanism include (1) avalanches, (2) fissuring (up to 3 miles in length involving supture of both ice and rock), (3) mudflows on the t
j south'and east flanks of the volcano, and (4). minimal melting of ice and j
BnoW.
t
[
7.
Monitoring at the Mount St. Helens site includes at least (1) seismometers, l
(2) tiltmeters..(3) aerial reconnaissance to observe snow conditions and possible
(
abnormal melting..and (4) infra-red photography to detect " hot spots."
,I 8.
Three reservoirs, located along the Lewis River on the southwest flank of the volcano, constitute a portion of a hydro-ele ~ctric' complex operated by Pacific Power and. Light Company. As a precaution the water level of Swift Reservoir, the uppermost lake, is being lowered in order to accomodate' a massive mudflow in the unlikely event one were to occur.
9.
The U. S. Fores't' Service has evacuated ils'own personnel from Gifford Pinchot National-Forest within which Mount St. Helens is located as well as permanent
}
' civilian residents near Spirit Lake on the volcano's north flank Residents i
have not been advised'to evacuate the nearest comunity-Cougar, Washington 1
(population 150) some 12 miles south of the volcano.
1 l
\\
t i.*
~
SU8880A88E M SATE D i
.....t............
l' IGC PORM 318 (9 74) NRQ4 0240 8 v... eevenmas sar *=>=reme errecu s 8 ove - e.e - te.
~
...-..a.
..:.Lu.
.. e....
k if"-y W
=
c g-q M
,s w
~
, APR 3 1980 l
- 10. The Trojan plant is'now in a " coasting down" mode at about 65% of power j'
(as of March 28) and is currently scheduled to shut down for refueling on April 9.
The shutdown of the plant has no connection with either the j
earthquake sequence ori March 20 or the volandic activity on March 27.
1 The planned shutdown had been initiated prior to the March 20 seismic activity.at Mount St. Helens.
This represent.s highlights of the status of the seismic and volcanic activity at Mount St. Helens as of noon, Tuesday, April 1,1980. - Additional pertinent.
i information will be disseminated by Harold E. Lefevre of the Geosciences Branch as,the need develops.
DISTRIBUTION:
' CENTRAL FILE Harold E. Lefevre, Geologist Geology and Seismology Section l
._Geosciences Branch, DSS i
Attachment:
k As ste'ced 1
cc '. w/ attachment H. Denton R. Mattson i
D. Eisenhut J. Knight L. Reiter L. Heller i
i R. McMullen H. Lefevre
_A. Bournia I. Peltier R. Black J. R. Gray GSB Staff J. Harbour
~
I L. Beratan l
R. Denise l
W. Gammill
{
M. Bell A. Schwencer
' C. Trar:nell J. G. Hanchett, Rev. V.
i E. Jordan-i T. Nova i t
k f(Nl &
f.hr,,1,,
I ome.*
- (
,,nss:ssg..... nsg;.g
= = = = >
..14Leftvrc:.st..LReiter:......; :.EJackson......
l
.....4/wa....
. 4m0.......
.4&ao..
=,.
., 3mc PORM 31s (9 76) NRQ4 (J40
- v.....wsa== s ar rasavia. orries t s'. s '. se e..
m._
.. e
. g 3..,g
h "s? ~m c h.st % er t
i:
GQ 0
T, V ".*u
[M g c$g g/-
L, Gb
%g, I % -
gjWd,:d,,
g 0. ce
[/T Seace N-. _k._w%9dh f2C =_=
j i
s A
tVA{HINGTON W "rce
\\.
Yr p I,W
-n :.:=v:=-
y
. \\ f3 Tacoma k1M%ife.,
'\\
kbI 79 2.Y: ' :+- "i
)
OL YMVs jR,yf E e-c;.., 9 :I-l -f>-cfoGsr h
{
E 345, e'/
l wPtts,t) l TsM& y' y"\\#W tT**.yWh Igm 5:
y'4%.nl.h ft.:
cos e c
R,er 4-QC. f',bl Saane A : 'd".
.s.
i u}
g
. R erv i
g
... - s s
fa....:5...l.$.[a M o..w 8
1 8 k%
Long,,.
I h'I\\ g '4ount st. Helens'50&i.h E
noJAW
$+
", ' " ' ~ '$5 &cN
~
k<%
t
\\
\\ - {k M W - 2 M ) M.?;"fI %
s _~rr =_.A{j;:_r_-.. _=__ -Tw=Q y
_{_ p---
fy
/>
s g
s, r_
g SALEM N-__
I
-J UECY
./
\\
ET*WCZ 7
= -m m-m-N N,s.
e a
\\
=0 t.se., ? '
'?
"l*=
X t
\\.__ 7 I
4 t
k OREGON Eusene C
. ?'
/
9 Tephra-hazard zones are outi,ned around Att St Helens. Wends blow from the volca.
section about 50*> of the time. About once no tos ud the sertocally and horizontally every 500 to 1,000 years, eruptions ssoIIpro.
shad =d sectrons of the map about 80?. of duce layers of tephra 15 to 100 cm thick mthin zone A. and2 to 15cm thscl ssi:hin i
the Inme, and toward the s ertic.'Ity shaded rone B. nu.S. GeologicalSun ev r aos mg
.O
.T T w N. 1..$
a n
L