Volcanic Hazards

Igneous Rocks and Volcanic Hazards

Volcanoes and volcanic eruptions might be the most feared and awesome geologic force that affects human civilization. Mount Saint Helens, which is one volcano in a string of volcanoes called the Cascade Range along the West Coast of Washington, Oregon and Northern California, erupted in May of 1980. This eruption killed 60 people and caused tremendous economic damage to the Pacific northwest in terms of damaged natural resources. Significant amounts of volcanic ash settled out of air in eastern Montana, and the ash cloud itself actually circled the Earth after a few weeks. However, 700,000 years ago, not all that long ago in terms of geologic time, a volcano in northern California erupted that was two orders of magnitude the size of Mount St. Helens. The volcanoes along the Pacific northwest are still very capable of producing future eruptions of this magnitude.

In Hawaii, the islands consist of one or more volcanoes that have built up from the seafloor to extend more than 10, 000 feet above sea level. The volcanoes on the main island of Hawaii are also very active, but the nature of the volcanism, and thus the hazards associated with them are very different than those of the Cascade Range.

In this pre-lab exercise you will compare and contrast the two volcanoes and use your growing geologic understanding to relate the differences in volcanism to differences in the characteristic and origin of the magma.

What to do:

Follow the links above (menu) to explore the two volcanoes: Kileau on Hawaii, and Mt. St. Helens (and the others) of the Cascade Range. After you feel you have sufficiently gone through the material, answer the questions below in written form. Your TA may require you to turn these in the week after lab for credit. If not, you will still be responsible for this material on all quizes and exams in the lab.

Click here for a printable page of the questions (requires Adobe Acrobat Reader).

Questions:

•What kind of magma (felsic or mafic) sources the volcanoes of Hawaii and the volcanoes of the Cascade Range?

•What is the tectonic setting of the Hawaiian volcanoes? of the Cascade volcanoes?

•How does the viscosity of the magma affect the "explosiveness" of a volcano?

•How does the composition of the magma affect the "explosiveness" of a volcano?

•What is the most significant hazards associated with the two volcanoes?