| What change occurred to the surface of the
volcanoes in order for plants to able to plant root?|
|Question Date: 2018-01-16|
The earth’s surface is a very active environment,
so after a lava flow cools and becomes a hard rock
we need to look at a smaller scale. When we
examine a thin section of a typical volcanic
rock, such as a from Hawaii, we see
that the rock is made up of different parts. These
include: several different minerals, void
space (pores), and glass.
Now the typical minerals in a basalt lava would
be tiny crystals of feldspar, pyroxene, olivine
and magnetite. The glass present is basically
a frozen liquid. Now as soon as the lava
solidifies and cools to room temperature chemical
reactions begin to break down the rock. For
example, the oxygen in the air begins to react
with the magnetite crystals to make a mineral
called hematite: You would call hematite
it rains, then the rainwater, which is slightly
acidic due to dissolved carbon dioxide, begins to
chemically weather the rock. That is the glass
begins to dissolve and the minerals react with the
rainwater to produce new minerals such as clay
minerals that are softer. Meanwhile winds blow
dust and pollen and small seeds unto the lava flow
that is beginning to break down into soil. Perhaps
insects burrow through the rock since it is porous
and rainwater will fill the pores… basically, the
biosphere will invade the rock as it breaks down
by chemical and mechanical weathering (freeze thaw
cycles adds to mechanical weathering).
There have been islands in the oceans that form
from below sea level and within a few years such
islands become habitats for life. Once microbes
start to grow, their waste products aid in further
chemical degradation of the rock….. Eventually
enough soil forms so seeds can germinate and begin
to grow. Many plants produce humid acid which when
combined with rain water enhances the dissolution
rate of minerals and glass.
If you want to learn more find a geology book and
look up. Weathering and erosion: chemical
weathering, mechanical weathering, soil formation
as KEY WORD on internet search.
Some scientists tested which nutrients are
important for plants to grow on old volcanoes. So
they took a lot of different fertilizers with
different nutrients. Then they traveled to old
lava flows on Hawaii and fertilized the plants to
see which nutrient helped plants the most. One of
the main ingredients in fertilizers, nitrogen,
actually ended up helping plants grow the fastest.
Plants grow differently on old volcano flows based
on weather, height above sea level, and lava type
as well. That means that the environment already
at a volcano helps decide how plants will grow
back after an eruption.
When lava freezes and becomes rock, it is actually
very similar to other common rocks like granite
and sandstone. The minerals and nutrients in lava
rocks and most other common rocks are pretty
similar. But most plants grow in soil, not rock.
So the main change that has to happen to the
surface of a volcano before most plants can grow
is that the lava rocks have to break down in the
wind and the rain to make soil. Soil forms from
rocks when they are slowly broken down by wind and
rain. When rocks break down to make soft soil that
plants can grow in, we call it “weathering"
Weathering happens to all rocks, but it is
very slow. After a volcano erupts and makes new
lava rocks, it can take a long time for them to
weather enough for plants to start growing; in
some places it takes a few years, in other places
it takes hundreds of years! Weathering happens
faster in places that are hotter and have more
rain (which is also where plants like to grow!
This is not a coincidence!). So a volcano in the
tropics will grow plants faster than a volcano in
All that being said, some plants don't need as
much soil as others. There are some plants that
grow directly on rocks and actually help break the
rocks apart with their roots, which makes more
soil for other plants to grow in!
So the main change that has to occur to the
surface of a volcano in order for most plants to
grow is that the lava rocks have to weather: the
lava rocks have to break down in the wind and rain
to make soft soil that the plants can grow in.
I hope this was helpful! Great question!
Volcanoes covered with plants aren't all that
different from any other pile of rock covered by
soil, except that the magma beneath will
come out. This means that the changes to the
surface of a volcano that allow plants to grow on
it are basically the same as those anywhere else.
You might be thinking of a volcano soon after a
lava flow, in which case the surface is all hard
rock. Wind, rain, and other weathering
erode that rock into soil. Over time, nutrients
that plants use are built up in the soil by
bacteria, other plants, and animals that travel
through the area. The ash and magma from the
eruption can also be very rich in nutrients
essential for plant growth, so the soil around
volcanoes is often some of the most fertile on the
planet. Seeds are carried to the soil by wind and
animals, and eventually the volcano may be covered
by dense vegetation.
The first plants to grow on rocks are flat
lichens . Lichens are plants with both algae and
fungus growing together. I read that it takes 100
years for a flat circle of lichen the size of a
quarter to grow on a bare rock. As the lichens
grow up above the rock a bit, they will collect
some dust and water from wind and rain. They also
break down a bit of the rock under them. Water
sits there and breaks down the rock some more,
creating bits of soil. Cracks in rocks also hold
some water and are a good place for other plants
to start to grow. Moss grows on cracks in rocks,
and seeds can fall into the cracks and sprout. And
as the primitive plants grow and die, they make
soil for seed plants to grow in. You can look at
what grows on rocks that are mostly bare.
Ash from volcanoes can also fall on plants, in
thick layers. That happened with Mt. St. Helen's
in the US, and I've read that trees grew great
Volcanic soils are generally very mineral rich but
volcanic ash drains very well, so plants growing
on fresh volcanic ash are likely to be desert-type
Thanks for the great question!
The soil on and around volcanoes can be some
of the best in the world for growing plants.
When volcanoes erupt, ash and lava cover the
surrounding land. While devastating in the short
term, in the long term an eruption creates new
soil. The new soil that forms after a volcanic
eruption is often very rich in all sorts of
minerals and nutrients that plants need to
take root. These minerals include sulfur,
potassium, and phosphates, which plants often have
a hard time getting.
When combined with heavy rainfall, volcanic
soil becomes very fertile, or good for growing
plants. For instance, think about Hawaii and how
green its rainforests are. That is in part
due to the rich volcanic soil of the islands and
the great deal of rainfall there.
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