MOUNT ST. HELENS - A spectacular new structure has formed inside the crater at Mount St. Helens, just in time for this weekend's opening of the Spirit Lake Highway.

A slab of rock the size of a football field is standing on end inside the crater.

The giant 'fin' is pushing upwards of four to five feet a day, but is not growing taller because it tends to crumble as it grows.

"Of course, the fin gets to about the height of a football field or so and then it starts to get unstable and we get rockfalls off the top of it, explained USGS Geologist Dan Dzurisin.

The fin joins another structure, nicknamed 'the whaleback,' as one of seven distinct structures that have grown and disintegrated since this eruption began in October 2004.

The growing fin is not the only thing changing inside the crater. While the fin is growing up, the dome is pushing outward at a rate of about a meter a day.

All of the changes have scientists anxious.

"It's been hard to get views," said Dzurisin. "It's been hard to keep track of what's going on. Now the weather's improving and we have an opportunity to go up there and study in a lot more detail what's going on."

If you would like to check out Mount St. Helens in person, the Spirit Lake Highway will reopen on Friday.

You will be able to head all the way up to the Johnston Ridge Observatory, where it costs just $3 to get an up close view of the crater.

Related links:

USGS volcano cam
Tourist information