skip navigation

Answers About The Petrified Forest

1. What makes The Petrified Forest unique?

  • We are home to the world’s largest petrified redwood trees, Sequoia langsdorfii, now extinct.

2. What does petrified mean?

  • It means that organic material of the once-living tree has been slowly replaced with minerals. This transformation occurs on the cellular level as minerals fill the voids created from dead cells to gradually turn living material to stone.

3. If these aren’t trees, what can I call them? Rocks? How about minerals?

  • These trees have become fossils. Fossils are the remains or traces of plants and animals that are preserved and, usually, exceed the somewhat arbitrary age of 10,000 years.

4. So these petrified trees are how old?

  • Scientists have estimated that these trees were petrified in a volcanic eruption that occurred 3.4 million years ago. While this may seem like a difficult length of time to fathom from a human perspective, if you consider that the earth is approximately 4.6 billion years old, this was a relatively recent event from a geological perspective. In fact, if all the years of earth history were squeezed into a 24 hour period, this eruption would occur about a minute before midnight.

5. Where is this volcano now?

  • Geologists have estimated that the crater of the volcano was located within a one mile radius of modern-day Mt. Saint Helena, approximately 7 miles to the northeast. Mt. Saint Helena is best described as the uplifted, folded, and eroded remnant of this volcanic activity; a product of millions of years of battle waged between forces of mountain building and erosion.

6. What was this eruption like?

  • The high silica content of the magma made it extremely viscous and hence unable to flow freely from the volcano. Volatile gases accumulated in the magma chamber until the pressure reached a bursting point. The tremendously explosive eruption that ensued sent pyroclastic flows screaming down the flanks of the volcano. This volatile mix of gases and volcanic debris traveled at hundreds of miles per hour and was as hot as 1000° C. Tons of volcanic ash, released during the eruption, blanketed the countryside.

7. How were these trees preserved in this cataclysmic event?

  • Volcanic ash quickly engulfed the trees to create a state of anoxia and prevent the trees from being instantly incinerated. Over the next tens of thousands of years, mineral-laden water seeped through the soil and replaced organic material of the trees with minerals, namely silica.

8. What are the sparkles I see on the petrified wood? And on the trail?

  • These are all varieties of the mineral quartz, which is in vast quantities in this environment as a result of past volcanic activity. After quartz replaced all of the available spaces within the trees that were once filled with organic material, excess silica was occasionally precipitated on the surface as a fine layer of crystals known as druzy quartz. Since these specimens of petrified wood have undergone complete replacement, we are able to see amazing details of the once-living tree. In fact, it is easy to see growth rings, and with the aid of a microscope you can discern individual cells!

9. Does that make these petrified trees as hard as a rock?

  • Absolutely! These trees are now mainly comprised of quartz, which is a very hard naturally occurring substance. These petrified trees are harder than steel! Quartz is also a very stable substance at the earth’s surface, which means these petrified trees will be around for millions of years to come.