Evening star., 1952-06-04
Safe Home Can Be Built
At Foot of Volcano Now
Study Shows How Strong WoIIs
Muy Divert Streams of Luvu
By Thomos R. Henry

NlUy 0IVStt StISuWS OF 6uNu
By Thomas R. Henry
Man now can build his home near the
foot Of a volcano in relative safety.
It is feasible to construct walls of suf-
ficient strength to divert lava streams
from inhabited areas, geologists Of the
United States Geological Survey have
determined after study of the 1851
eruption Of Mihara Yama in Japan.
Gated by the staff Of the volcano re-
search laboratory operated by the Sur
vey in Hawaii. as
On steep slope. according to the re-
port of geologists Arnold G. Mason and
Helen L. Foster. pressure from the lava
flow can be terrific. This often has
been demonstrated in the past. But, they
say. this force can be greatly decreased
by locating a wall where it does not face
q steep slope, placing it below forest or
rocky distractions or by establishing
such distractions as rock cairns. The
pressure also can be reduced by excavat>
ing moat on the uphill side Of wall
to break up the straight downhill flow.
A large swift stream of lava. the geolo-
gists believe, can be stopped by q wall Of
moderate strength. If 1t is protected by
uphill distractions.
Stopped ON Steep Slope.
During the 1850 Mauna Loa eruption
in Hawaii. according to report from
the Surveys observatory, lava flow
which advanced rapidly down a steep
slope toward the sea was stopped tem-
porarily by four -foot-high loose stone
wall across its course. The lava piled up
and spilled over the wall without push
ing it over.
Another Hawaiian example was the
diversion Of q flow from Mauna Xxi
in 1920 by q loosely laid stone wall
only q few feet high. The direction
Of fiow was changed by about so de-
grees % that 1t ran parallel to the
wall for about 40 feet. In 1885 un-
cemented stone walls confined Q lava
pool on the northeast side Of MaunA
Loa. until 1t rose sufficiently to over
now the walls.
Another case cited by tho Survey
geologists was the blocking of lava by
rubble masonry walls bounding three
sides Of o cemetery adjacent to Q
destroyed church on the south slope Of
Mt. Vesuvius. This apparently weak
wall was sufficient to conflne q tongue
Of lava that entered from the church
side.
Overtopping Of wall by an accumu-
lation Of lava. the report points out.
constitutes q greater problem than that
Of building wall strong enough to
withstand heavy flows. This is particu-
larly true where great volumes of lava
are likely to be emitted, or where sue
cessive flows override CONCEALED earlier
flows.
A new type Of airborne magnetometer
has been developed at the Naval Ord
nance Laboratory here which will make
possible O new magnetic map Of the
world.
The old magnetometer developed for
detection Of submarines during the war
measured from the air changes in the
total intensity of the earth's magnetism.
It has proved Of great value in prospec-
ting for minerals over relatively inacces-
sible areas and also for mapping land
under ice. The new instrument meas
ures not only the intensity but the
direction Of the magnetic pull.
At present charts for land areas are
produced from data obtained by point
to-point measurements made on the
ground. Measurements over oceans by
this method ceased when the non-rnag-
netic ship Carnegie of the Carnegie
Institution of Washington burned in
Samoa in 1929. The planets magnetic
field constantly is changing. Charts for
the ocean areas now are Of questionable
value.
Continuous Records.
Airborne surveys with the new instru-
ment will be Of comparable accuracy
with the surveys Of the Carnegie. They
have the added advantage Of producing
continuous records and saving much
time. The instrument also can be used
for surveys over polar regions for which
magnetic information virtually 10 nom
existent due to inaccessibility by ship
or on foot. This holds true, for example,
Of the greater part Of the Antarctic con-
tinent. There is very little Information
about conditions under the Greenland
ice cap.
The new magnetometer already has
been tested on short flights Of the type
Of planes which the Navy photographic
ONCE will use in magnetic surveys.
Further long distance test flights. 1t u
expected, will start this month.
Altogether, the Naval Ordnance Lab
oratory scientists feel they have pro-
vided one Of the most effective tools
for the future explOrer