Volcanic Ash (Tephra): Evidence of the Passage of Time

Eichholz Maar in Germany. The Praclaux maar today is completely filled with sediment and is no longer a lake but rather a meadow but in the past it might have looked like this.The following example is derived from several articles involving sediment cores from explosion

The following example is derived from several articles involving sediment cores from explosion craters (maars) and their subsequent analysis (See refs at end).  I will assume little geological background in writing this example.

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Summary:  Pollen profiles from a 46 meter core from the center of a small explosion crater in South Central France suggest a long history of climatological changes in that area. These sediment cores also reveal the presence of volcanic activity after the creation of the crater in question. It does not appear possible to accommodate the pollen and tephra record from this crater core with a 4000 year time line if we apply the modern creationist assumption that the crater was formed at or after the end of a global flood.
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Here is some of the basic background information necessary to understand this particular problem:

A) A 46 meter core of lake sediments from the center of the Praclaux
explosion crater in south-central France is reported. The bottom of the
cored section doesn’t even represent the beginning of the sedimentary record
after the explosion that created the crater since they didn’t reach the
volcanic rock at the base.

B) Two significant layers of tephra (volcanic ash) were observed one at
almost 22 meters the other one at 44 meters. The first is 70 cms thick the
second over a meter thick. Tephra is characterized by the lack of organic
material and has signature form depending on the volcano it came from
(because the glass crystals that make up ash differ depending on the
ejection rate and temperature – basically every volcano and even each
separate explosive event has a fingerprint).

The presence of these “ash” layers suggests that after the explosion
creating this particular crater two other large volcanic events (from other
volcanoes) must have occurred at widely spaced intervals afterward.

C) Another crater in the area (Rabains) has had a 30 meter core taken and
it does not contain any tephra layers in it at all indicating it blew after
the Praclaux volcano and even after another two other volcanic events that
deposited the 44 and 22 meter tephra layers in the Praclaux crater. Other
volcanic craters nearby show evidences of many more volcanic eruptions and
thus are thought to be older than the Praclaux crater since they contain
tephra from volcanic eruptions prior to and even including the Praclaux
eruption. (note: the tephra layers from different cores in other craters can
easily be compared because of the unique properties of each tephra layer)
Overall the authors consider the Praclaux crater young compared to most
others in the area.

D) People have lived in this part of France for at least 2500 years if not
much longer with no reports of ash-fall (thus reason for tephra layers in
the chronology) much less any volcanic activity whatsoever in all of western
Europe. It seems safe to assume that something would have been said in
some records at some time about 70 centimeters of ash (probably double this
amount since it is compacted) falling in the area. This suggests that at
the very MOST 21 meters of sediment (of the 46) were deposited during this time.

E) The core section contained sections of only sand and silt, clay or
organic clay. Pollen samples were taken 368 times at close intervals along
the whole 46 meters and the types of pollen grains identified in each
sample. A pollen diagram (percentages of particular types of pollen types at
a particular depth) was then constructed. The pollen diagrams show dramatic
changes in the types of pollen (and thus presumably the types of plants
growing in the area). Some examples:

Picea (Spruce pollen) – Spruce pollen is found only in layers corresponding
to 40.5-46, 30-31.5, 25-29, 17-25 meters. In these areas 10-70% of the tree
pollen is (all other depths Spruce accounts for only 0-2%). Other tree
pollens are found only sporadically in the column such as fir, beech, and
oaks. Pine pollen is common almost all the way through the column except at
31-33 feet where rather being 20-80% of the tree pollen it is rather 0-2%.
At this same depth yews, firs and beech tree pollen are at the highest. In
fact, at 31 meters there is no pine pollen but there is 40% fir pollen and
30% beech pollen then just a foot above that 0-2% of the pollen is fir and
beech but 80% is pine. From 30 feet up there is a very high percentage of
pine pollen but never any beech or fir pollen again (note: presently a
pine/deciduous forest surrounds the crater with no firs or beech trees in
the area and none have been known from modern human history there – at
least 2000 yrs).

What is even more interesting than the changes in pollen ratios is the
correlation between pollen types. Mixes of plants one would expect to see
together are represented in their pollen ratios. When there is a lot of
pine pollen (indicative of a pine forest in the area and thus a warmer
climate generally) there are no firs or beech trees. When there is a high
percentage of spruce and fir there is almost no pine pollen and therefore
presumably no pine trees. Pine pollen accounted for up to 80% of all tree
pollen grains in many samples while was nearly absent in others.
Overall the authors find strong evidence for at least five temperate forest
episodes (pine and oak) alternating with phases indicative of colder
climates (spruce, fir, beech).

The tephra layer at 21 meters is interesting because before and after the
layer the types of pollen are very different as one would expect if an area
got coated with ash. The pines go from near 80 percent of the pollen to
almost none right after the tephra. Grasses and other herbaceous plant
pollen suddenly increases, for example: pollen of the Apiaceae – (carrot
family ie. weedy things) more than quadruples and then is reduced over the
next couple of feet. All of this is what one would expect given that ash
might wipe out many trees and alter the soil. The pines are knocked over or
killed and other trees and plants that can handle the poor soil and sunlight
come in but are eventually shaded out by new pine trees once the soil is
reworked. This process alone would probably take 100 years at a minimum to
get back to a fully fledged forest with the balance of pollen grains seen
only 1 foot above the tephra layer.

Because no volcanic activity is known in modern times in this area (the 21
meter tephra layer of 70 centimeters has been linked to a volcano more than
100 kilometers away and so would have been a very memorable volcanic
experience). At least the 25 meters deposited below the 21 meter tephra
level must predate man’s habitation of the area. Even if that 21 meters
were deposited in the last 2500 years that would mean there would had to
have been phenomenal amount of deposition before that to squeeze it into the
1500 years available after the Flood. Where did those deposits come from.
There isn’t much flowing into the area because of the height of the lake so
the opportunities for deposition of sediments is slim. Also the vegetative
changes recorded in the pollen profiles suggests a succession of at least 5
different temperature forests alternating with periods of cold-climate
forests (spruce-fir type forests). Only the temperature forest is know to
man in the area for at least 2000 years but significant numbers of spruce
pollen grains are found right up to 17 meters and almost none above that
(less than 1%).

Other volcanic crater cores are more complex and record much longer periods
of time. Some have many tephra layers requiring many separate volcanic
events going back farther than the two events recorded in the Praclaux
crater. Since the tephra layers are separated by sizable layers of
sediments containing changing pollen profiles indicative of new growth and
succession after an ash-fall event it seems reasonable that long periods of
time took place between the volcanic events. When did all the volcanic
events occur especially given the amount of time it takes for a temperature
forest to grow on top of new ash or in this case in the crater of a volcano.
Consider also that the original volcanic crater would have remained
extremely hot for many years (if not centuries – try calculating the time
for a 3-500 meter thick magma core to cool to the ambient temp that it is
now or even to a temp in which plants would be able to colonize). As I
pointed out earlier the crater we are dealing with in this example seems
young compared to others as IT’S tephra from its explosion is in layers well
ABOVE others in other volcanic craters although it is not the youngest as
the tephra layers inside its own crater attest.

Remember that none of this 140 feet of sediment is rock and needs to be
explained as post-flood since it is in a crater of a volcano that spewed ash
out that landed on tope of over 10,000 feet of presumed Flood-deposits.

I use this example because it is relatively simple but there are many more
examples that are much more complex but I think even much more compelling.
10 to 30 individual tephra layers are not uncommon in sediment cores of
lakes and wetlands in places around the world. Most of these tephra layers
would be separated by sediments with similar pollen profiles.

One of the most dramatic examples can be seen in the 911 meter long core of
the sediments of Lake Biwa in Japan (the largest fresh water lake in Japan).
Takemura (1990) reports 54 tephra layers the closest to the surface being
only 10 meters from the lake bottom. This lake is
present on a volcanic island itself so the Japanese island had to be built
up even before the lake could form and start collecting sediments.

Seems to me that the simplest explanations for some of these observations
is that a long period of time was required to produce them. How might I
otherwse explain the pollen and tephra layer data?

Another simple question also presents itself with these examples. If most
of the 46 meters or 911 meters of soil were deposited early (i.e.
immediately after the Flood) why haven’t these sediments changed to rock??
911 meters is over 2500 feet of soil. Am I to believe that in all other
places in the world sediment layers put down by the flood quickly turned to
rock all the way up to several meters from the surface when these sediments
over 1000 feet down for over 2000 years don’t show any signs of changing to
rock any time soon?

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Refererences:

Reille, M., and Jacques-Louis De Beaulieu. 1995. Long Pleistocene Pollen
Records from the Praclaux Crater, South Central France. Quaternary Research
44: 205-215.
(primary resource)

Reille, M. and J-L. De Beaulieu. 1990. Pollen analysis of a long upper
Pleistocene continental sequence in a Velay maar (Massif Central, France).
Palaeogeography, Palaeoclimatology, Palaeoecology 80: 35-48.

Beaulieu, J. L. de, and Reille, M. 1992. Long Pleistocene pollen sequences
from the Velay Plateau (Massif Central, France), I: Ribains maar.
Vegatation History and Archaeobotany 1: 233-242.

Takemura, K. 1990. Tectonic and climatic record of the Lake Biwa Japan,
region, provided by the sediments deposited since Pliocene times.
Palaeogeography, Palaeoclimatology, Palaeoecology, 78: 185-193

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