1. One half of the radioactive potassium-40 (K40) in an igneous rock has decayed to argon-40 (Ar40). According to the ESRT, about how many years ago was this rock formed?

(1) 1.3 x 109

(2) 2.6 x 109

(3) 3.9 x 109

(4) 9.8 x 109

2. State one difference between dating with radioactive isotope Carbon-14 and dating with the radioactive isotope uranium-238.

Carbon-14 can date organic remains.

Uranium-238 has a longer half-life.

VolcanoesFamous Eruptions

Volcanic debris

Types of volcanoes and lavas

Hazards and benefits of volcanoes

Lava Types

Viscosity- a fluid’s resistance to flow.

High viscosity- Low viscosity-

Slow moving

High silica content

Fast moving

Low silica content

Rhyholitic (felsic) Basaltic (mafic)

Volatiles- trapped gasses and liquids in a molten material

Increase explosiveness of a volcano

Stratovolcano (Composite volcano)

Mt. St. Helens

http://www.classzone.com/books/earth_science/terc/content/investigations/es0907/es0907page03.cfm?chapter_no=investigation

May 17, 1980 Harry Glicken, USGS August 13, 2005 Valerie Smith

Before and After the Eruption

Shield Volcano

Mauna Loa, Hawaii

Cinder Cone

Paricutin, Mexico

Caldera

Crater Lake, Oregon

Pyroclastic debris- deposits of volcanic origin

Volcanic debris

Blocks- greater than 64 mm in diameter

Lapilli- 2-64 mm in diameter

Ash- less than 2 mm in diameter

Bombs- greater than 64 mm in diameter (molten material)

Tuff- rock composed of compacted fragments of volcanic origin

Nuée ardente- fast moving, glowing, cloud of gas and ash

Volcanic debris

http://www.geo.mtu.edu/volcanoes/hazards/primer/pyro.html

Volcanic debris

Mudflow (aka: lahar)- the rapid downhill flow of a mixture or rock fragments, soil, and water.

Can travel tens to hundreds of miles away from the volcano

Associated with snow covered mountainsMt. Rainier (OR), Mt. St. Helens (WA)

http://www.classzone.com/books/earth_science/terc/content/investigations/esu301/esu301page08.cfm?chapter_no=investigation

Volcanoes Around the Universe

Io

Large moon of Jupiter

Similar size and density to Earth’s moon

Most volcanically active body in our solar system

Mt. St. Helens

Famous Eruptions:

http://www.classzone.com/books/earth_science/terc/content/investigations/es0907/es0907page03.cfm?chapter_no=investigation

May 17, 1980 Harry Glicken, USGS August 13, 2005 Valerie Smith

Before and After the Eruption

Mt. St. Helens Facts:• It is a stratovolcano (or composite volcano), located in

southwest Washington State.

• May 18th, 1980, 8:32 am (PDT).  Eruption was triggered by a 5.1 earthquake centered beneath the mountain.

• The massive ash cloud grew to 80,000 feet (18 kilometers) in 15 minutes and reached the east coast in 3 days.  Although most of the ash fell within 300 miles of the mountain, finer ash circled the earth in 15 days and may continue to stay in the atmosphere for many years.

• 57 people were killed as a result of the eruption.  Of these, 21 bodies were never recovered from the blast zone.

Blow Down Forest

1981 2004

7,000 big game animals, 12 million Chinook and Coho salmon, and millions of birds and small mammals are believed to have died in the eruption.

Mt. St. Helens Eruption Picture From the Deck of Hoffstadt Bluffs Visitor Center

Mount St. Helens Re-born - Oct. 4, 2004

Current Eruptions December 15, 2007

Popocatepetl, Mexico

Giant plume of ash and steam spewed up to heights of 3,000 m (2 miles)

Volcanic ash from a single eruption can be deposited in a thin layer on the ground worldwide. Ash deposits can help with relative age dating of rock strata.

Risks Associated with Volcanos

• Loss of land, livestock, homes (etc), trees

• Weather is affected by ash particles in air

• Injuries, deaths of humans

Benefits of Volcanoes

• Soil around volcanoes is rich with minerals for plants/crops.

• Geothermal heating of homes close to volcanic regions.

• Hot springs.

• Tourism.