|I saw a picture yesterday on the newspaper online
of lava flowing from rocks in Hawaii. How is this
Lava flows in Hawaii are generally really slow
moving and extremely hot! As they emerge from the
volcano, the lava flows begin to immediately cool
as they interact with the much cooler air around
us. As the outer edges of the lava flows cool,
they begin to form a crust but the center of the
lavas flows remain very hot and have the ability
to continue moving. Think about a hot lava
cake, a chocolate crust encases a gooey chocolate
inside; this is just like Hawaiian lava flows!
The crust that forms actually protects the inside
of the lava flows from the air outside, keeping
the inside warm and gooey. Sometimes, lava can
pool up beneath that crust creating so much
pressure that it will actually burst through the
edge of the crust! When this happens the flows
emerge from beneath the crust and flow in a
different direction and then form a new crust.
So the lava isn’t actually flowing FROM the
rocks in Hawaii, the flows are actually flowing
beneath this sometimes-thick crust of hardened
lava. This crust can become very thick and
sometimes the lava flowing beneath can form
tunnels, or lava tubes, in which the lava can
freely flow and maintain its heat and eventually
may emerge from beneath these rocks once they make
it to the ocean.
The Hawaiian islands are thought to be formed
through a process called hotspot volcanism,
whereby each island is formed from one or more
volcanoes. Geoscientists think that a hot plume
of material originating from near the
core/mantle boundary (~2900 km below the Earth's
surface) has built the islands over time. This
material is heated and rises buoyantly - like
material in a lava lamp - until it erupts onto the
ocean floor. Once this happens, later eruptions
'grow' each volcano over time, leading some to
emerge from the ocean and become islands.
The island of Hawaii (called "the Big Island")
is actually built from multiple volcanoes, and
some are still active. The photo you saw likely
came from one of these active volcanoes. The
eruptions at this stage are not explosive and are
therefore not dangerous; this allows people to get
very close to the lava as it erupts. Once the lava
cools, it forms basalt - the same type of
rock the islands are made of. In summary, these
lava flows are the result of active volcanism in
the Hawaiian Islands.
Rocks are kind of like ice cream. Sometimes rocks
get really hot and can melt and become lava. When
they get cold they turn into solid rock again.
Some rocks are easier to melt than others.
Those which melt easily usually aren't as hot when
they come out as lava on the surface. The rocks
in Hawaii are harder to melt, and they come
out at a higher temperature than other kinds of
When I was a kid I visited some of my family in
Hawaii and saw the volcanoes there. The lava was
hotter than a campfire. If people threw any sticks
into the lava, they would burn right up.
I don't know exactly what you saw, but remember
that lava is molten because it is hot, and
freezes when it is colder. The air is colder
than the lava, so molten lava touching air will
form a layer of frozen rock on the surface, with
still molten lava underneath. The frozen lava
on the surface looks like a rock because it is a
rock , but it can still flow or the
still-molten lava can break out because it is
hotter underneath the surface.
Lava is melted rock. If you heat rocks above
1112 F (600 or 700 degrees Celsius) they start to
melt, just like ice/snow starts to melt when
you heat it above 32 degrees F (0 degrees C). The
lava that you saw pictures of in Hawaii is
extremely hot, which is why it is liquid.
There aren't very many places on Earth that are
hot enough to melt rocks, but Hawaii is one of
them. This is because Hawaii has volcanoes.
Volcanoes are where very hot lava from inside
the earth (the mantle) comes to the surface of the
earth. It is still very hot when it gets to
the surface of the earth, but it starts to cool.
That lava that you saw in the photo will only
be liquid for a few hours before it starts to cool
and become solid.This is how rocks are formed!
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