Hawaiian Type

The Hawaiian type, represented by the volcanoes of the Hawaiian Islands, has abundant outpourings of basaltic lava in which the gases are liberated more or less quietly. Explosive eruptions are rare, but fountains of lava, projected by jets of escaping gas, may play at heights up to 1,0.00 feet and more. The product is basic lava with only minor amounts of cinder, and ash. The outpourings of lava develop flat lava domes, forming, as in the case of Mauna Loa, some of the largest mountains on earth.

Strombolian Type

Stromboli, a volcano in the Aeolian Islands off the coast of Sicily, is in a constant state of activity and since ancient times has been known as the "lighthouse of the Mediterranean." The eruptions of Stromboli consist of more or less regular explosions of moderate intensity, which throw out pasty, incandescent lava (scoria) accompanied by a white vapor cloud. The lava in the center crusts over lightly, and at intervals of about one-half hour the pent-up gases escape with mild explosions, hurling out clots of lava and fragments of the crust. Many of the fragments fall back into the crater to be blown out again, but others fall on the slope of the cone and roll into the sea.

Vulcanian Type

The term Vulcanian is from the island of Vulcano, also in the Aeolian group. The lava from Vulcano is more pasty and viscous than Strombolian lava, and it forms a thick, solid crust over the crater between the infrequent eruptions. Gases accumulate beneath the congealed crust, and in time the upper part of the magma column becomes thoroughly gas-saturated. Finally, with strong explosions, the obstructions are blown out and the broken fragments of the crater plug, together with some new lava in the form of “breadcrust bombs” and scoria, are ejected. When the plug is suddenly blown out, the gas-saturated magma is disrupted into pumice and ash by the explosively expanding gases. After the obstruction is cleared, lava flows may issue either from the crater or from fissures on the sides of the cone.

Pelean Type

Pelean is derived from Mont Pelee, on the island of Martinique, which erupted in 1902, destroying the city of St. Pierre with the loss of more than 30,000 lives. The Pelean type produces magma of the highest viscosity and is characterized by extreme explosiveness. The distinguishing feature of the Pelean eruption is the nue ardente, or “glowing cloud”. It is a highly heated gas, yet is dense enough to maintain contact with the surface as it rushes down the slopes of the mountain with hurricane force. It was such a cloud that overwhelmed St. Pierre. In Pelean eruptions, the upward escape is frequently blocked by a plug of lava in the crater, and the explosions break out as horizontal blasts from beneath the plug. The magma is expelled as a highly ash-charged gas and no lava issues except that pushed up as a viscous plug in the crater.

Fred M. Bullard

Adapted from Volcanoes of the Earth

DRAFTING

1). Choose one of the following subjects, or, with your teacher’s approval, another subject for an expository essay:

· classes in school

· occupations to consider

· inventions

· medical science

2). Make a list of the ideas and details you would like to include in your essay. Read over your list to see what it suggests with regard to natural groupings of information. Let the material guide you as you begin to select a principle of choice.

3). List three possible bases for classifying the material in your essay. Be sure each basis will be broad enough to cover all your material.

4). Review your list of bases-and select the most promising principle of choice. Put a check next to that basis.

5). Make an outline using the groups suggested by the basis for classification as main headings. Fill in details from your notes as the subheadings.

COMPOSING

Write an essay of classification based on your outline. Work through your outline one section at a time, writing about the material in each group. Use as many paragraphs, as are needed to effectively write about your subject. Be sure to include transitions between the para­graphs to link the ideas and to make their relationship clear.

REVISING

Ask yourself the following questions:

· How is each grouping of material introduced and developed?

· In what ways is the development of each group similar to that of other groups?

· What additional details, if any, are needed to fully explain each main thought or idea?

· What transitions, if any, would help link groups of material?

Make any changes that are needed to improve your essay.

PROOFREADING

Proofread your essay, following the steps in the Proofreading Checklist on page 142. You may have to make corrections in sentence structure, capitalization, punctuation, or spelling.

A. Think about how the material in the paragraphs was classified.

1. What principle of choice, or basis for classification, did the author use?

2. How many groups are included in the classification? Name them.

3. How are the groups consistent with the author's principle of choice?

4. How does the classification break up the material into understandable parts?

B. Think about the material included in each group of classification.

1. Does the author present the same sort of material about each volcanic type?

2. What information does the title of each grouping give?

3. What does the material in each group say about the intensity of explosions?

4. What information is given in each grouping about the frequency of explosions?

5. What does the material in each group tell about the products of explosions? What is told

about the effects?

6. How is the information in each grouping organized for presentation?

C. Think about the following subjects for expository writing. Imagine that you are preparing to classify material on

each subject. music plants

food habits

games exercises

dreams machines

Ø Think of two bases for classification for each subject.

Ø Which of these bases would be complete for the material you would like to present on the subject? How can you tell?

Ø How many groups would you have for each subject? What would these groups be?

Ø Are all the groups you selected consistent with your basis for classification? If not, which ones are inconsistent? How are they inconsistent?

SUMMARY

· Classifying means organizing material into groups based upon simi­larities.

· To classify material, a writer must select a basis for classification.

· This basis must be complete, or at least broad enough to cover all the known material.

· The basis must be applied consistently in selecting groups of mate­rial.

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