Young Explorers survey Tanzanian volcano
- Ol Doinyo Lengai
Thirty-eight Young Explorers
recently took part in a scientific expedition to Tanzania
where they used Leica Geosystems’ equipment to carry out
survey and geosceintific measurements of the active volcano,
Ol Doinyo Lengai. The students, part of the BSES
Expeditions, completed a gravity survey using Leica GPS530
receivers, as well as a digital terrain model of the volcano
crater and height measurements using the new Leica TPS1205.
“The Mountain of God”
Africa’s Great Rift Valley has many
spectacular sites. In the Grogory Rift south of Lake Natron
in northern Tanzania is a unique active volcano. Ol Doinyo
Lengai, which means The Mountain of God in Maa, the language
of the Maasai who live in this desolate region, is up
against the western wall of the Rift, and towers above it.
It is unique because it is the only volcano in the world
that erupts natrocarbonatite lava. This looks like very
fluid black oil, but rapidly turns white as it absorbs
water. In the dry season this can happen over a few days,
but in rainy weather the lava turns white immediately. This
can give Ol Doinyo Lengai the appearance of being snow
Trekking up Longido as
a warm up to the trek across the floor of the Rift Valley.
At two o’clock in the morning on 19th
July 2004, 38 Young Explorers, with nine Leaders arrived at their
camp site in the shadow of Longido some one hundred kilometres to
the east of Ol Doinyo Lengai. These Young Explorers were a BSES
expedition who would walk across the savannah on the floor of the
Rift Valley to Ol Doinyo Lengai then climb its steep flanks before
trekking across the Crater Highlands to mankind’s birthplace at
Oldupai Gorge on the edge of the Serengeti plains.
BSES Expeditions (formerly ‘The
British Schools Exploring Society’) came into existence in 1932 from
an educational idea by Commander George Murray Levick RN, a member
of Captain Scott’s final Antarctic expedition of 1911 to 1912. BSES
Expeditions aim is to deliver a once-in-a-lifetime experience that
is both challenging and fun and to develop essential skills in each
of the Young Explorers taking part including leadership,
communication and teamwork skills that will help them in the
future. The aim of BSES Expeditions is “To provide young people
with an intense and lasting experience of self-discovery in
a demanding and natural
wilderness environment”. Although exploration is a key part
of such an expedition, BSES also involve the Young Explorers
in scientific activities.
Fires – Ecology, Geoscience and
Aged between 16 and 20,
although most were on the younger side, these Young
Explorers were are divided into three Fires, a Fire being a
group of a dozen or so Young Explorers with two Leaders, a
good number to sit round a camp fire! The largest Fire
concentrated on the Ecology of the region and their prime
objective was to study the diversity of vegetation and birds
across the Rift Valley and due to altitude on Ol Doinyo
Lengai, the active volcano and an extinct volcano near by,
Gravity Meter readings
being taken with the position and height being fixed using
the Leica SR530 GPS in digfferential mode. The Young
Explorers are also recording the position wioth an eTrex
handheld GPS to compare its accuracy for a Navigated
position compared with thay from the Leica SR530 GPS and the
final computed position.
The two other Fires were Geoscience
and Survey whose their activities were closely related. The main
task for the Geoscience Fire was to carry out a Gravity survey
during the trek across the Rift Valley and on the slopes of Ol
GPS Base Station at the camp at the base of Ol Doinyo Lengai with 12
hour occupation to link the GPS observations into the IGS
Stations at Malindi with check observations to Mbarara and
the Seychelles. The Leica TCR702 was used to relate Gravity
Meter readings local to the camp to the GPS control.
Backpacking the leica SR530 GPS across the savannah. Hanna (one of
the Young Explorers) is in front with the battery and Colin
(the expedition Leader) follows with the Leica SR530 GPS.
The need for accurate heights
provided the Survey Fire with one its the two main science
tasks. The Gravity meter measures the pull of gravity and
the last count on the dial is equivalent to a mere 0.03m in
height, although accurately reading this is extremely
tricky, so we needed to achieve relative heights between
successive gravity reading of better than 0.1m. In order to
achieve this requirement Leica GPS530 receivers were used in
differential mode. Four primary locations were occupied for
up to 12 hours and these were computed as base lines back to
the IGS (International GPS Service) Station at Malindi on
the Kenya coast, with checks to IGS Stations at Mbarara in
Uganda and in the Seychelles. These provided bases from
which differential GPS observations were taken for each
location of readings with the Gravity meter.
Work in a harsh environment
Leica GPS SR530 receivers
proved their worth in this harsh environment and worked
faultlessly throughout the expedition despite the heat and
dust and being used by inexperienced people. Using check
bases and closed traverse we were able to establish that the
precision of the results were better than 0.1m in both plan
and height with many of the points showing much better
results than this, so we achieved our goal in an efficient
manner. During the course of the expedition the Leica
SR530 receiver, aluminium tripod and gravity meter were
backpack packed to some very difficult locations. Not only
was it taken to the top of Ol Doinyo Lengai and used to
traverse down its precipitous flanks but it was also taken
up the western wall of the Rift Valley to the complete the
gravity traverse across the valley floor.
Digital Terrain model of active
The other major science
project carried out by the Survey Fire was to produce a
Digital Terrain Model (DTM) of the active crater of Ol
Doinyo Lengai. The ideal Instrument for this was the newly
launched TCRP1200 with its long-range Reflectorless
measurement capabilities. A TCRP1205 and lightweight
Aluminium Tripod were backpacked up the very steep path to
the crater on the summit of Ol Doinyo Lengai. A strenuous
climb of some 2000m in altitude so the light weight of this
Instrument was a blessing. This Instrument also worked
faultlessly in the harsh environment found in the crater of
an active volcano again despite being used by inexperienced
people who achieved excellent results after only a short
lesson in its operation.
Plane Table Surveying around Kerimasi base camp. (Camilla and Megan).
The Young Explorers had benefited from using modern
sophisticated Leica Geosystems equipment. To show them the
basic principals of making a map and how errors were easily
made if care was not taken with setting up and orientation
they were introduced to Plane Table surveying.
Plane Table Surveying around Kerimasi base camp. (Camilla and Ben).
Kerimasi, an extinct volcano is in the background with a
Maasai manyata on the left.
The new batteries proved to
be a major benefit. Not only were they very light so did
not add much to the heavy loads of water and food that
needed to backpacked to the top to sustain those staying up
there and carrying out the survey observations, but their
long levity meant that they did not need continually
bringing down, recharging and taking up again, and when they
did need charging it did not take long minimising the
intrusion of a generator running at base camp.
Determining the height of Ol Doinyo
Another task performed by the
Survey Fire were to determine the height of Ol Doinyo Lengai
by accurate measurements using the TCRP1205 to a point
established using the Leica SR530 receiver relative to the
IGS Station at Malindi.
Our last camp on the rim of Ngorongoro Crater. This is a wild
elephant that has wandered into the camp to help himself to
fruit that is easily accessible in the camp supplies.
This has to be the most accurate
determination of the height of this mountain ever made, but its
value could become superfluous next time Ol Doinyo Lengai erupts.
We established that the summit of Ol Doinyo Lengai has an
Orthometric Height (height above mean sea level) of 2951.6m whilst
the GPS, or Ellipsoidal, Height was established as 2962.2m. This
exercise fits in neatly with the use of Leica SR530 GPS receivers to
determine the height of nearby Kilimanjaro as reported in Reporter
The team also took advantage
of the GPS measurements to compare the accuracy of a
Navigated GPS solution compared to the Computed result.
Being close to the equator there was good GPS satellite
coverage thought the expedition and the results showed that
the Navigated positions made with the Leica SR530 receivers
were within 5 metres of the computed position in plan and 10
metres in height, although the majority were within 5 metres
in height, whilst the Navigated positions provided by the
small hand held Garmin eTrex receivers were within 15 metres
in plan, but up to 75 metres different in height.
Creating awareness of surveying
The Young Explorers benefited
from using modern sophisticated Leica Geosystems surveying
equipment. This was offset by introducing them to Plane
Table surveying around the camp to show them the basic
principals of making a map and how errors were easily made
if care was not taken with setting up and orientation.
Ol Doinyo Lengai from our camp nearthe shores of Lake Natron. As a
result of the Syurvey measurements made by the Young
Explorers with the Leica SR530 GPS and the Leica TCRP1205
Total station, we established that the summit of Ol Doinyo
Lengai is 2951.6m above maen sea level.
The BSES expedition to Tanzania was
an opportunity to bring awareness of Surveying (Geomatics) to young
people starting out in life and into their schools as many of the
Young Explorers are now back at school completing their final year
before going on to University. This type of activity, together with
innovations such as Geomatics.org, which makes Surveying equipment,
such as Leica levels, available to Schools and to BSES Expeditions
during the summer months, will bring our profession to the attention
of young minds. This safari will be deeply embedded in the minds
and remembered fondly, by those that took part, for the rest of
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