The document discusses two volcanoes - Mount St. Helena in California and Mount St. Helens in Washington. It explains that 3 million years ago, an eruption from Mount St. Helena covered the area in ash and buried massive redwood trees, which later became petrified and now make up the world's largest petrified forest. It also describes the 1980 eruption of Mount St. Helens, how it blew down surrounding trees and the extensive damage caused. The document provides details on how wood becomes petrified through replacement with silica minerals and how the eruptions of these two volcanoes led to the formation of famous petrified sites.

1. The Petrified Forest
October 2007

2. What does petrified mean?
• Greek root “petro”
– Meaning “rock” or “stone”
• Example: From Harry Potter
– People became PETRIFIED, turned into stone

3. Mount St. Helena
• 3 million years ago
• Suspected that Mount St. Helena erupted 7
miles NE
• Sandy ash left as the soil
• World’s Largest Petrified Trees - Redwood
http://en.wikipedia.org/wiki/Image:Mount_Sa
int_Helena_%282007-10-08%29.JPG

4. Located in Calistoga, CA

5. • All the petrified tree tops point in a
Southwest direction away from the
volcano
• Which supports the hypothesis that the
blast knocked the trees over

6. Another Famous Volcano
• Mount St. Helens (WA)
• Exploded in 1980
• Trees were blown down parallel to a lateral blast from
the volcano and shows tops pointing away from source

7. • Trees are snapped easily
like toothpicks

8. Mount St. Helens
Visited in Summer 2006

9. After 28 years, hardly
anything has grown back
around the area of the
volcano.
Water has carved through
the ash to make rivers

10. Mount St. Helens has shown signs of life in the past few years. It has
started smoking from its vent, number of earthquakes have increased.

11. Eruption of Mount St. Helens
Mount St. Helens Eruption
October 2004 Eruption

12. • Trees at Mount St. Helens were not buried
in ash
• They will not be petrified

21. Discovery
• Discovered in 1871, Charles Evans
• Found a stump of petrified wood while
tending his cows

22. • 1914, purchased property by Ollie Bockee
• Developed the land by charging 50 cents
admission
• Used funds to pay geology students to
excavate more trees
• Discovered that these trees were the
world’s largest Petrified Trees!!

23. How does wood become petrified?
• Water that has silicates in the ash seeped
down into the gaps left behind by the
decomposing tree fibers
• This replaces the wood cell by cell
• Wood is preserved from lack of oxygen

24. What are the wood cells replaced
with?
• Crystalized silica
• Until the tree became stone
• Some of the silica has agatized into a
colorful glass-like gemstone

25. What are silicates?
•
•
•
•
Minerals, rock forming minerals
Such as quartz
Make up most of Earth’s crust
Petrified wood can have different colors
Following is a list of contaminating elements and related color hues:
carbon - black
cobalt - green/blue
chromium - green/blue
copper - green/blue
iron oxides - red, brown, yellow
manganese - pink/orange
manganese oxides - black

26. • Petrified wood can preserve the original
structure of the wood in all of its detail
• Tree rings and tissues

27. The Numbers (Mt. St. Helens – WA)
•
•
•
•
•
Trees blown down: 4 billion board feet
Lava volume: 120 feet deep in places
Lava temperature: At least 1,300 degrees Fahrenheit
Slide area: 23 square miles
Property damage: 27 bridges, nearly 200 homes, 185
miles of highways/roads
• Effect on Columbia River: Reduced channel depth
from 40 feet to 14 feet
• Wildlife casualties: Killed in the blast were 7,000 deer,
elk and bear; all birds and most small mammals; 12
million chinook and coho salmon fingerlings in hatcheries
and an estimated 40,000 young salmon in the wild
• Cost of damage and cleanup: More than $1.1 billion
http://seattlepi.nwsource.com/mountsthelens/summary.shtml

28. What caused Mount St. Helens
eruption?
• 5.1 earthquake centered beneath the
mountain
Mount St. Helen Facts and Information