We are at lake Rotomahana, in the Rotorua area.
It's quite a volcanically active area.
The big volcano that you see in the background here
is mount Tarawera. It erupted in 1886 and it was a devastating eruption.
It totally changed the lake.
the lake became much bigger, and the fissure from Mount Tarawera
runs right down the center of this lake, and it is still active today.
There is a lot of Geothermal activity that we can see on land
up the Waimangu Valley here, but also underneath the lake.
So we're here today
as part of a survey to look at the ammount of heat
that's coming out at the bottom of the lake here.
We are using a new technique.
We have the thermal blankets. On the top we have a thermometer or thermistor,
and this measures the temperature, and then we have a second one on the bottom
that measures the the temperature on the bottom of the blanket.
The bottom of the blanket sits right on the mud or rock on the bottom of the lake.
The top of the blanket is recording the temperature of the water at the bottom of the lake.
What we're interested in is the temperature difference between those two.
That temperature difference tells us how much heat is coming out of the bottom of the lake.
And that's what we call heat flow.
we have 10 of these blankets that we have been deploying across the lake,
and the idea is to distribute these in about 100 different locations/ sample stations
to measure the heat flow across the entire bottom of the lake.
This is the first time we've ever used these blankets
in the lake environment.
The density of measurements that we've made in this lake
has never been done before.
To deploy these blankets we lower them over the side of the boat
we get rid of the air bubbles then we start lowering the blanket very slowly down to the bottom.
It's about a hundred meters down so it takes about five minutes
for us to lower it slowly by hand to the bottom of the lake.
Once it hits the bottom of the lake, the line goes slack.
We put a little float on the top and then we let it go.
We leave the blankets on the bottom of the lake for about 24 hours.
The following day we pull the blanket up by hand or by winch.
We pull it onto the boat and then drive over to another sample station
and redeploy it to take the next reading.
This is a recording from one of the thermal blankets for the first four stations.
on this axis here you can see the temperature and the range is about
a three degrees from top to bottom so each one of these
is a day-long recording all the snow blanket the curves that you see the top
curve here
is the curve on the bottom of the blanket when it sits on the bottom of
the lake
and held the thermistor
comes to settle down to the temperature of the mud
then the bottom trace here
is the temperature at the bottom on the lake water
so and as the semester that sitting on top of the black kid
and the essential measurement that we have is
once this has come settle down we see the
the difference between these two measurements and that is a measure
what the heat flux is coming out with a bomb so on the first
three stations that you see the blanket is cooling off
and we see little bit of heat flow coming out from these these actually
fairly significant heat flows
this one on the end is a very
strong heat flow its gonna almost
wanna have to agree difference and that
compares to approximately 30 watts per square meter which is very high
for heat flow measurement okay so here's a map of the
deployment stations on Lake and you see about
100 this thermal blanket stations here
is a very strong very strong hire me here
very strong he flowed in here and
in here and these are
very very high more than 50 watts per meter squared which is
amazing really in fact we've got the
more recent measurements that now show so almost 90 what's coming out the
bottom
my career as all scientist studying heat flow
I really have not seen anything this strong this is an incredible
wall mount he you know the long-legged
the
the new
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