1.  What is the Juan de Fuca Ridge?  Where is it located?  How is it related to volcanoes?

The boundary between the Pacific and Juan de Fuca Plates is marked by a broad submarine mountain chain about 500 kilometers long, known as the Juan de Fuca Ridge. Young volcanoes, lava flows, and hot springs were discovered in a broad valley less than 8 kilometers wide along the crest of the ridge in the 1970's. The ocean floor is spreading apart and forming new ocean crust along this valley or "rift" as hot magma from the Earth's interior is injected into the ridge and erupted at its top.
 

2.  What is a composite dome?  How does it differ from a lava dome?

Composite Dome: The dome at Mount St. Helens is termed a composite dome by scientists, because it represents the net result of many eruptive events, not just one event. The dome-building process may be pictured as the periodic squeezing of an upward-pointing tube of toothpaste or caulking compound. The process is dynamic, involving the upward movement of new material, cracking and pushing aside of old material, sloughing of material from steep surfaces of the dome, and occasional, small but violent explosions that blast out pieces of the dome.

Lava Domes: Volcanic domes are mounds that form when viscous lava is erupted slowly and piles up over the vent, rather than moving away as a lava flow. The sides of most domes are very steep and typically are mantled with unstable rock debris formed during or shortly after dome emplacement. Most domes are composed of silica-rich lava which may contain enough pressurized gas to cause explosions during dome extrusion.
 

3.  What is talus?

Talus occurs as extensive aprons mantling the flanks of the dome and in irregular patches high on the dome. The talus accumulations comprise one of the most conspicuous features of the dome. Most of the talus formed from hot rockfalls during extrusion and rapid endogenous growth; only a minor amount was generated by cold rockfalls during periods of quiet. Hot talus blocks developed radial prismatic jointing during cooling. Renewed movement (slumping, rockfalls) broke the fragile, jointed blocks into several joint-bounded pieces and further contributed to the talus accumulation.
 

4.  Why is the Mauna Kea volcano considered the largest mountain on earth?

The Hawaiian shield volcanoes are the largest mountains on Earth. Mauna Kea Volcano rises 13,796 feet above sea level but extends about 19,700 feet below sea level to meet the deep ocean floor. Its total height is nearly 33,500 feet, considerable higher than the height of the tallest mountain on land, Mount Everest in the Himalaya (29,028 feet above sea level).
 

5.  How were the Hawaiian islands formed?

See information in: http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/description_hot_spots.html