1 / 9

CHAPTER 18: VOLCANOES SECTION 1: MAGMA

CHAPTER 18: VOLCANOES SECTION 1: MAGMA. Objectives: Standards:. CHAPTER 18: VOLCANOES SECTION 1: MAGMA. Magma: is a mixture of molten rock, suspended mineral grains, and dissolved gasses deep below Earth’s surface Magma forms when:

womackj
Download Presentation

CHAPTER 18: VOLCANOES SECTION 1: MAGMA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER 18: VOLCANOESSECTION 1: MAGMA Objectives: Standards:

  2. CHAPTER 18: VOLCANOESSECTION 1: MAGMA Magma: • is a mixture of molten rock, suspended mineral grains, and dissolved gasses deep below Earth’s surface Magma forms when: • Temperatures are high enough to melt rock (between 800 oC and 1200 oC ) • Temperatures exist at the lithosphere/asthenosphere border • Magma is less dense than the surrounding rock • Forced upward

  3. FACTORS THAT AFFECT MAGMA FORMATION TEMPERATURE: • Temperatures increases with depth. • This is why the asthenosphere is plastic-like. PRESSURE: • Pressure increases with depth due to weight of rock above. • Pressure explains why rocks in Earth’s lower crust and upper mantle do not melt even though the temps are high enough WATER CONTENT: • Water can be found in the spaces of rocks. • A wet mineral or rock will melt at a lower temp than a dry rock.

  4. BASALTIC MAGMA CHARACTERISTICS OF BASALTIC MAGMA: • Rocks in upper mantle melt and rises to crust quickly • Low viscosity – fluid magma • Small amounts of dissolved gases • Small amounts of silica • Quiet/non-violent eruptions

  5. ANDESITIC MAGMA CHARACTERISTICS OF ANDESITIC MAGMA: • Found along continental-oceanic subduction zones • Oceanic crust and/or oceanic sediments melt • 60 % silica • Intermediate viscosity – thicker than basaltic and intermediate gas content • Intermediate eruptions

  6. RHYOLITIC/GRANITIC MAGMA CHARACTERISTICS OF RHYOLITIC/GRANITIC MAGMA: • Continental crust • Rich in silica and water content • High viscosity – thickest magma, slows movement • Large amounts of trapped gases • Very explosive eruptions

  7. VISCOSITY AND HOW IT AFFECTS THE EXPLOSIVENESS OF MAGMA Viscosity: A substance’s internal resistance to flow. • EX: water has a lower viscosity than honey and flows more easily. • Honey has a higher viscosity than water because it does not flow as easily. Viscosity and explosiveness of magma: • The lower the viscosity, the more fluid-like the magma, the least explosive eruption. BASALT • Intermediate viscosity, intermediate magma, intermediate explosion. ANDESITIC • The higher the viscosity, the less fluid-like the magma – magma gets caught and pressure builds up causing a more explosive eruption. RHYOLITIC/GRANITIC

  8. TABLE 8.1 – PG. 474.

  9. SILICA CONTENT AND VISCOSITY OF EACH TYPE OF MAGMA Hotter magma or lava = lower viscosity • Basaltic: temp. between 1000 oC and 1250 oC – low viscosity • Rhyolitic: temp between 700 oC and 900 oC – high viscosity High amounts of silca = higher viscosity • Basaltic: low amounts of silica = low viscosity • Rhyolitic: high amounts of silica = high viscosity • Andesitic: intermediate amounts of silica = intermediate viscosity

More Related