did lava flow from mt. st. helens
The next eruptive period, the Castle Creek period, began about 400 BCE, and is characterized by a change in composition of St. Helens' lava, with the addition of olivine and basalt. The pre-1980 summit cone started to form during the Castle Creek period. Significant lava flows in addition to the previously much more common fragmented and pulverized lavas and rocks (tephra) distinguished this period. Large lava flows of andesite and basalt covered parts of the mountain, including one around the year 100 BCE that traveled all the way into the Lewis and Kalama river valleys. Others, such as Cave Basalt (known for its system of lava tubes), flowed up to 9 miles (14 km) from their vents. During the first century, mudflows moved 30 miles (50 km) down the Toutle and Kalama river valleys and may have reached the Columbia River. Another 400 years of dormancy ensued.
Mount St. Helens