Transient Electromagnetics Survey - the final push! Days 7th, 8th & 9th September

So our final survey is also geophysics. Transient Electromagnetics or TEM allows for deeper penetration and therefore deeper imaging of the sub-surface, approximately 150m. 

TEM can take quite a while to set up, but the survey is generally quite quick to run. The aim was to use the GPR to guide the laction slection for the TEM. This was possible on some occasions, but on others I had to use other information, hypotheses and inferences to guide location selection. 

The set up involves laying out a copper transmitter coil, with the aim of the larger the coil the greater the penetration depth. So as often as possible, the 100m x 100m coil was used. This had to be laid out in a square, which straight away on such terrain was challenging. Disappearing over a hill so the start point is out of sight often led to diamond shaped areas that had to be corrected as best as possible. Laying this out took four os us. Yes there are three of us, so we had a huge amount of help from our driver. 

Me sat at the receiver computer with the receiver coil in the foreground. It reminds me a little of the globe drinks cabinets popular in the 80's.

Once we were happy with the coil layout, we then had to layout and connect the transmitter, receiver coil and the receiver computer along with a preamp. Everything needs protecting form the sun and moisture, hence umbrellas and plastic bags! Not very scientific.

TEM is used to record the electrical resistivity of the sub-surface. As lithologies change with depth, so does the resistivity. If there is a fault, the offset should be picked up based on the offset of the resistivity. 

The principle's of TEM are based on Faraday's law of induction and Lenz's Law. The copper transmitter coil is energized by a direct current which after a time appropriate for the coil size, is quickly cut off. A nearly identical current is induced in the sub-surface to preserve the magnetic field produced as a result of the original current, or eddy currents. Ohmic losses means that the induced surface currents dissipate causing changes in the magnetic field. These changes cause subsequent eddy currents. The net result is a downward and outward diffusion of currents in the sub-surface which resemble an expanding smoke ring. The currents produce a a magnetic field, the changes (flux) at the surface of this field is measured and the way the currents diffuse in the subsurface depends on the conductivity/resistivity of the sub-surface lithologies. 

Image from www.epa.gov

I hope that makes sense! 

I haven't seen any of the data produced by this survey, as it all needs processing with specialist inversion software when I return to the UK. 

Our final day with the geophysics equipment involved taking everything with us. Trying to squeeze it all in the car made for an interesting half hour. 

Our lunch joins the GPR antennas on the roof. We just about fit everything in. Talk about a logistical jigsaw puzzle!

The final day didn't go to plan as the transmitter didn't record a current when we first turned it on. We tried everything to eliminate the problem in the hope that we would be able to tweak the survey. Batteries changed, cables changed, coil sections checked, connections checked and even a different coil, but no luck. So after almost 4 hours of trying, we packed up with 2 TEM surveys not completed, one of which is potentially very important! Very frustrating, but what can you do?

Well that's it, all 5 surveys done in 5 weeks, with a few days off and a few big hiccups thrown in for good measure. 54 GPR seismic lines, 5 TEM surveys, 34 open extensional fractures measured, 7 fumaroles observed with 2 surveyed in detail, almost 320 CO2 efflux data sets and just shy of 700 soil gas samples collected, we are done. It is going to be a busy few months going through everything to interpret the meaning of it all. 

End of fieldwork treat, we are off on a Game DRive at Nakuru National Park. Wish us luck to catch the lions who are famous for being in the trees.

Lala Salama from Kenya!

Geophysics begins - the tough stuff! Days 30th and 31st August, 1st, 2nd, 3rd, 4th and 9th September

So it's time for the tough stuff, GNSS, GRP and TEM. What the devil are they I hear you ask? Well I shall try my best over the next few blogs, to take you through them.

First things first, the GNSS. The Global Navigation Satellite System is a constellation of satellites providing signals from space transmitting positioning and timing data, it provides global coverage and the in our case accuracy of 2mm.

First attempt at setting up the GNSS

As you can probably tell, the first attempt to set up took some time and completely baffled the memory afetr training took place about 5 weeks prior. This set up took about an hour and a half. The set up on the last day, took about 20 minutes!

It is very important when doing large surveys, to have as accurate a location as possible. The above image contains the base station, there is also a rover, which came everywhere with us and was even connected to the GPR (see below).

Beth (right) has the rover on her back in this image, though I appreciate it is not the best image (she is communicating with aliens apparently!) Mairi with the GPR computer

The GPR is Ground Penetrating Radar. It allows us to see shallow structures that in the case of Menengai, have been buried by the young lavas. GPR has never been done in this area, so we really didn't know what results we would get, if any at all. It's penetration depth is estimated to be around 10 meters for this kind of environment. 

We had with us 4 different antenna strengths, 25, 50, 100 and 250 MHz, the lower the frequency, the deeper the electrical signals will penetrate, or the greater the attenuation depth. But with increased depth, you sacrifice clarity of imaging. We used the 50's and 25's which surprisingly sometimes gave us penetration down to 16m and 32m respectively.

Survey team ready to go!

Construction of the 25MHz antenna

GPR survey with the 25MHz antenna. Beth leads controlling the pace size, I'm in the middle monitoring the image that is slowly growing on the computer screen and controlling the 'firing' of the , Mairi bringing up the rear checking how parallel the antennae are. 

For those of you reading this who are familiar with some geophysics field techniques will undoubtedly notice the fence next to us. Thankfully it was only for the first 80 meters of the section. But the importance of completing a comprehensive geophysical survey anywhere has been highlighted during the past 5 weeks. Menengai is well on the way to being a fully developed centre for power production. The pylon bases are cropping up everywhere and the huge steam pipes are being installed as well as the start of construction of the sub-station. 

Trying to find survey areas where the signals won't be affected by ringing caused by the presence of metal was a huge challenge. My very personal opinion of this locality is that not enough surface surveys were completed, surveys that include geophysics. 

Comprehensive and detailed surveys ranging fully from geophysics, gas sampling, fluid sampling, temperature surveys, geology mapping and cross sections and trial wells, among many many others should be completed. Some of these surveys were completed, but in the area of geophysics, the surveys were minimal. Yes, they are costly, but will save in the long term because money is not spent putting in deep, expensive wells that then don't discharge. 

So what is GPR?

GPR is a geophysical method that uses radar pulses to image the subsurface. It is a nondestructive method that uses electromagnetic radiation in UHF/VHF frequencies of the radio spectrum. The high frequency radio signals are transmitted in to the ground and the reflected signals are returned to the receiver and stored. The computer calculates the time taken for a pulse to travel to and from a target in the subsurface.

.Image from http://people.uwec.edu/

So why are we doing this kind of survey?

The equipment is on loan from NERC Geophysical Equipment Facility in Edinburgh. 

The location of all the faults and fractures within the caldera are inferred at the very best, and even less is known about which are actively used for fluid and gas movement. The reason the locations are unknown is because young lavas from eruptions as recent as 200 years ago, have buried the surface traces of these structures. Knowing where these features are and which are active, is of vital importance when planning to utilize and develop power from geothermal sources. 

Menengai is now well developed as I say, but it has provided the opportunity to develop hypotheses after last years visit and develop methods by which to test these hypotheses, as well as test the equipment capability in such environments which will contribute to guiding future research techniques in the field. 

Mairi grabbing a much needed 40 winks after a 6am start to avoid the 2pm storms

So for now, Lala Salama from Kenya!

Direct Use projects and sundogs - 1st September

After a morning of GPR surveys (see a separate blog) and seeing the best sundog, it was time to visit the direct use projects taking place in the caldera.

Great example of a sundog

One of the many things that the people associated with the Menengai Geothermal Project are keen to achieve is more than electricity. The team are trying to find and develop as many direct use applications as possible. Last year when I visited (girlsonfieldwork.blogspot.co.uk Day 4) There was a direct use trial involving fish and plants.

This year whilst here, not only have they further developed some of their ideas but there was an official two day launch of some of the direct use projects, with further projects given the green light.

It is very exciting to visit these projects and see the passion in the team. The applications to you and me might seem comparatively small, but what these applications could mean to the local communities around the caldera and the potential positive impact to the lives of many, is huge.

There are four direct use schemes that have just started to run in the caldera, linked together in a cascade system. The schemes have been set up on the well pad of MW-03, which is currently venting, with power generation from this well at 2-3 MW.

A schematic of the cascade system

Tito, who is one of the leads on the projects first explained how the heat exchanger worked. Cold water from nearby tanks arrive at the well pad under gravity and is fed in to a large coil. This coil is surrounded by super-heated brine water that is rising from the well. The interface between the super-heated water and the coil is the point of heat transfer to the cold water. The cold water is heated to around 75°C before being piped to the direct use projects. Once the brine water from the well has been used, it is transferred to a pond, where there are plans being developed for further uses. Nothing is wasted.

The heat exchanger

The first project is The Dairy. Here the hot water is used to pasteurise the milk. The milk is inside a drum constantly being stirred. This milk is surrounded by a jacket that is filled with the water that has been heated by the heat exchange process. Once the milk reaches a temperature of 68°C, the hot water is removes from the jacket and replaced by cold water, the milk is constantly stirred throughout the entire process.

Tito talking to Mairi about The Dairy

Some of the hot water from The Dairy is then moved to the The Laundry and used to wash items in a washing machine and the heat is also used for drying. Vincent our driver volunteered his clothes to be the first washed in the 'Geothermal Laundry'.

The remaining water from The Dairy is transferred to an area where aquaculture is taking place. The water is still at a temperature of around 40°C and is mixed with cold water to lower the temperature to the optimum fish temperature of 29°C. This temperature along with feeding is carefully monitored, producing fish that grow at twice the rate of fish in 'normal' environments. I did ask if such rapid fish growth had any affects on the fish, but apparently not. It was compared to humans flourishing when they find themselves in an environment they love (our holidays on sunny beaches!).

Discussing the aquaculture geothermal project with Tito

As with last year, the water from the fish tanks is filtered away carefully to keep the tanks clean. The ammonia from the fish excrement is filtered out of the water so that once again it is clean. This fish water is then used to water over 876 tomato plants inside a geothermally heated greenhouse. The greenhouse is only heated at night, as the day time sun heats it during the day. It has been estimated that each of these tomato plants will have a yield of 30kg per season, with two seasons' per year. The ammonia is diluted and used to feed the plants as the plants will extract the nitrate from the ammonia.

In the geothermal greenhouses

These small projects are now up and running and it is hoped that local farmers will use The Dairy and that the community will benefit from the aquaculture and agriculture methods in the very near future.

The people who live in and around the caldera do not have much, but these projects will soon help them provide further for their families, improving the lives of many.

Open extensional fracture mapping - 22nd and 23rd August

Last year, some large features were observed, but appeared to have little to no off set along them, suggesting they were not faults.

Before leaving for this field season, I developed a map using satellite imagery, identifying where with in the caldera these features appeared to be. So one of the surveys is to find as many of these features as possible and collect data. The data to be collected include: dip, strike, depth, width, off set (if any) and direction of down throw (if any).

The location of most of these features, believed to be open extensional fractures, appear to be in the centre of the caldera. Due to the lavas in the centre, we would be limited as to how many we could access. For safety, only those that could be accessed from roads and well pads would be obsevered and recorded.

Inside the termination point of an open extensional fracture

Many of the open extensional fractures observed appear to pinch out at each end and accessing the deepest point of the fractures was not always possible. We used a hand held DISTO laser measurement equipment for the width and depth. 

Inside an open extensional fracture

Standing along the strike of an open extensional fracture

We found some of the features identified, not to be open extensional fractures, and also found that access to even those near roads and well pads, very difficult. Altogether, we only managed to collect data on 34 of these features. It is hoped that the data can be used to establish whether, as seen in parts of north-east Ethiopia and northern Tanzania, the extension is this region is now accommodated by dyke intrusions, or if it is still being accommodated by faulting.  

This was a short survey, therefore a short post, so,

Lala Salama from Kenya!

Steaming ground survey - days 15th, 16th and 17th August

Over the next couple of days we completed a detailed survey of the steaming grounds situated almost at the centre of the caldera, very close to the location where I believe part of the structural ring fault sits below the young lavas.

The steaming grounds and fumarole were very active last year and although the temperatures are still very high, there does not seem to be as much steam. Published isotope data has already demonstrated that the main source of the steam and therefore the main Menengai recharge source is Lake Nakuru approximately 8km to the south.

Lake Nakuru along with most of the rift lakes of Kenya and possibly parts of Ethiopia have flooded in very recent (2-3 years) and are yet to recede by a notable amount. The amount of flooding far exceeds that of the annual average rainfall for the region. The reasons for the flooding though unknown, already has hypotheses associated to the phenomena and will hopefully be investigated in the near future.

So two main hypotheses to explain why the steaming grounds and fumaroles at this locality are less vigorous in comparison to last year are (1) despite coming to the end of rainy season, it has been a much dryer few months. So the addition of  meteoric water to the system, through rainfall has dropped. This would need testing from the aspect of infiltration speeds, heating and circulation. It might be that the system circulates and heats the fluid at a rate that would not support this hypothesis. (2) MW-10 is just a few 10's of meters to the north of these steaming grounds and fumarole. It has just completed the drilling of a directional well that cuts directly beneath the steaming grounds, targeting the feature responsible for the fumarole. This will have created a conduit for the steam to escape along at a much quicker rate with less resistance.

So on to the survey. We completed a detailed grid map of a section of the steaming ground. The location for this was identified based on early morning observations of where there was a higher amount of steam escaping to the atmosphere.

Mairi recording some data

We created a 10m x 10m grid, split in to 2m x 2m squares. The GPS co-ordinates of the corners of the 10m x 10m square were recorded. Then a grid sketch was made of the key features and the positions where temperatures were recorded from, the temperatures were noted and the strike of any fractures. The highest temperature recorded during this survey at 11cm depth was just over 78 degrees Celsius. We had predicted very early on that the temperatures would be higher the closer to the fumarole we surveyed. Though this became apparent very early on, the second part of the survey actually demonstrated the ground temperatures immediately over and around the fumarole were generally lower. 

In addition to the data collected as described above, we also collected three soil gas samples and data on the CO2 efflux in the centre of each 10m x 10m square. 

Me completing soil gas sampling and efflux recording

This part of the survey covered 2400m square, which due to early starts, we managed to complete in two days, including the end of the last day when we got caught in a very heavy down pour and thunderstorm. The rain drops are huge in Kenya and so cold! 

The second part of the survey, originally had been planned the same as the first. However on looking at the slope and knowing the challenges we had moving the grid from one section to the next, I changed it. So instead of detailed grid mapping of the area, we did 4 transects starting at the top of the slope.

Working down slope on one of the transects, with MW-10 in the background

Each transect was 30 meters long and spaced 10m from the next. The grid co-ordinates for the start and the end of each transect was recorded. At every 5m, starting at 0m, the temperature at 11cm depth was recorded and additionally at every 10m, starting at 0m, on transect 1 and 4, soil gas samples and CO2 efflux data were collected.

I hope this survey will present data that will show the changes in the shallow sub-surface behaviour of fluids and gases depending on where the samples were collected in relation to any major features, eg. a fault. From this, it should then be possible to make some inferences that due to the environment being similar, this behaviour also occurs at other fumarole localities across the caldera. 

The total area covered was just under 2500 meters square. Here's hoping it worked! :-)

Lala Salama from Kenya! 

Soil gas sampling, the student becomes the teacher, days 12th, 13th, 14th, 18th, 20th & 21st August

Today the real work begins and I woke up feeling a little nervous.

After spending a month on the Canary Islands, myself being taught how to do soil gas sampling and the concepts behind the accumulation chamber method for efflux data collection, it was time to pass on what I had learnt to my two field assists Beth and Mairi - just a little scary for a moment!

I'm lucky that both Mairi and Beth are quick at picking up new things, so it wasn't long before they were getting on with the survey at hand.

The area to be surveyed is 77 km square and we have about 6 days to complete 300 sample sites. Each sample site is approximately 200 meters apart and follow the road network that has been constructed in the caldera, for ease of access.

Soil gas sampling involves knocking a stainless steal rod in to the ground with a hole through its length. at the top there is a rubber septum that a needle is inserted through. This needle is connected to some tubing, valves and a syringe. The syringe is used to draw the gas from the ground. The first time the syringe is filled, the collected gas is used to 'flush the system', which in turn reduces the possible effects of contamination from the atmosphere. More gas is sampled also, to flush the vials for the same reason.

Mairi soil gas sampling

Showing Beth the 'PP' efflux equipment - kindly on loan from Oxford University

Beth on soil gas duty

Both girls getting stuck in by well MW-01 venting at 35MW

During this survey, the extra site we got to see include being in the right place at the right time and catching well MW-07 discharge for the first time.

This was something I never thought I would get to see, so a first for me too!

Sampling in the south of the caldera was very hot and very peaceful, but very pretty - we did have our driver on leopard watch. Though they are nocturnal and would move away if they heard us approach, most of the caldera's resident leopards are mothers with young, so we have to be extra vigilant. 

A short time out to take in the serenity of the southern part of the caldera

Trucks as wide as the lanes - only in Kenya! The installation of the steam pipes, X-ray checks of the welding of the pipes and the start of the installation and construction of the Menengai sub-station.

We also met this inspirational young woman Gathoni, a female Drilling Engineer and rig supervisor at just 28 years old and a perfect role model for young girls here in Kenya. As her rig is currently awaiting the go ahead to start drilling, she took some time out to talk to us about the rig and how things work. Though we were kitted out in our personal protection equipment, we were not allowed on the rig, but were able to have a bit of a walk around the well pad so Gathoni could point things out to us as she talked about them and the equipment role in the bigger process. 

Myself, Gathoni, Mairi and Beth

Steam pipe installation near the site of the Menengai sub-station

The rods we use for the soil gas surveys become very blocked every day. And although most of the time we manage to unblock them enough to finish a days work, it is likely that they would get blocked to a point where they can no longer be used. So we found a garage on our way back to our accommodation where they had a power washer. Every day Ailisha would clean the probes for us, so the inside of each was completely clar for the next day.

Equipment cleaning!

The survey team grows by two!

Mairi soil gas sampling with an audience!

One day's worth of soil gas samples!

So that is our soil gas survey almost complete. We just have 28 sites left to do along the south rim of the caldera, which is planned for the end of August. We had hoped to have already completed this survey, but we got lost. So we are waiting for the availability of someone who knows where they are going a lot more than I do!

Lala Salama from Kenya!

What and Why?

So after last year's fieldwork, I developed a geological map of the caldera in it's entirity. All the maps of the caldera that I have managed to find so far are from the late 50's and 60's. And though these maps are really quite beautiful in that they have been done by hand (I could look at geological maps for hours! Bit geeky? Maybe! But who cares!) Never be afraid to be yourself, and if that means you're a bit of a science nut, then so be it! You will be successful in all your endeavours and the world needs more of us!

Trying to get rock samples out of Kenya can be a challenge, as several permits are needed, the rocks need to be checked for any economic value (and if found to be so, they may be taken from you), there is of course the cost of shipping them also. So the map does not contain specific dates of individual flows, but is based on observations made in the field with regards to age relations of one flow to the next. There is some literature available with dates of some of the youngest lavas, so it is possible I could add some dates at a later stage.

The idea behind developing this map was to look at the flows and the relations with the localities of the drilled and proposed wells. The map also provided striking evidence for the possible location of a ring fault, something that has largely been inferred. In addition to this inference, inferences have also been made as to the location of faults and fracture networks. Having a good understanding of the locality of such features, especially those that are active conduits for gas and fluid movement, is of vital importance in understanding geothermal systems.

Here at Menengai, the locations of these features are largely based on inferences because any surface traces have been buried by the very young lava flows associated with the post-collapase resurgent volcanics of the Upper Menengai Sequence (McCall, 1958-1959).

So based on last years observations, map development, LiDar and satellite imagery and further research, the plans for this year are as follows:

Soil gas sampling and in situ CO2 efflux data collection - the soil gas sampling involves drawing gas form a depth of 40 cm down in to syringes, the samples are then transferred to vials. Over 300 sites have been sampled across the caldera with 2 samples collected at every site and a further third sample collected at approximately 15% of the sites. The samples will be analysed at the InVolcan labs on Tenerife, looking for quantitative values of CO2 and Helium using micro-gas chromatography and quadrupole mass spectrometry, with the third samples analysed for 13C/12C ratios using isotope mass spectrometry. These gases are the first to rise to the surface from a magmatic body and are therefore perfect gases to target. The efflux data is used to determine the amount of diffuse degassing occurring in Menengai - the degassing no one sees! Collectively this data can be used to generate sequential Gaussian simulation (sGs) maps that will identify the locality of active faults and fractures buried below the young lavas, a key requirement for geothermal development and system modelling. Further to this, the data can also be used to monitor how much CO2 Menengai is degassing naturally to the atmosphere in relation to climate change, and for volcanic risk monitoring of volcanoes that are still classed as active.

Soil gas sampling (and educational filming commitments! in the Canaries)

CO2 efflux data collection in the Canaries, using the accumulation method with a Leica sensor - slightly different to the sensor to be used in Menengai - but does the same job.

An active volcano does not need to be erupting to be classed as active. Any volcano that has erupted in the last 10,000 years, has shown to have ground movement (inf;ation and/or deflation) recorded by geophysics and InSar satellites and has active fumaroles, geysers and springs is classed as active.

Further surveys connected to above include detailed mapping of a steam field where soil gases will be collected, CO2 efflux data, surface temperatures and thermal imaging.

Additional surveys include Ground Penetrating Radar and Transient Electromagnetics. As neither of these surveys have been completed in Menengai before, it is very difficult to predict how the electrical signals used with behave; what the attenuation depth will actually be and how much signal scatter there might be.

I checked with GDC on arrival and found that all the surveys I have  planned to complete during this field season, have not yet been completed. This is quite exciting, as it allows for the development of further data that will complement the data already available, testing the capability and relevance of the methods and equipment to be used.

So keep watching to see how we get on.

Lala Salama from Kenya!