Eruption Products

PART ONE - LAVA FLOW TYPES

BASALTIC LAVA

Where do basaltic lava flows erupt from?

• Shield volcanoes
• Rift zones
• Cinder cones

Fluid lava flows can be subdivided into:

• Pahoehoe Lava -- Surfaces are smooth, billowy, or ropy.
• A'a Lava -- Surfaces are fragmented, rough, and spiny, with a "cindery" appearance

Pahoehoe Lava



Charateristics of Pahoehoe Lava

• Relatively thin (1-2m)
• Very fluid
• Low Viscosity

Pahoehoe Lava can be further divided into 3 different types:

• Ropy Pahoehoe - lava surface is bunched up or wrinkled and resembles a coiled rope
• Sheylly Pahoehoe - contains a billowy flow top with a frothy vesicular surface skin, only a few centimeters thick, overlying large cavities, generally 5-30 centimeters thick
• Slabby Pahoehoe - contains a series of closely spaced slabs, a few meters across and a few centimeters thick, broken and tilted by mass movement, or drainage, of the underlying lava.

A'a Lava



Characteristics of A'a Lava

• Cindery fragments broken during the churning action of flow advancement.
• Thicker than and less viscous than pahoehoe lava.

ANDESITIC LAVA

Characteristics of Andesitic Lava

• Blocky nature of lava flows
• High viscosity
• Relatively high thickness (some thick enough to form lava domes)

DACITIC TO RHYOLITIC LAVA

• As silica content and polymerisation increases, the viscosity of dacitic and rhyolitic lava increases.
• Although dacitic-to-rhyolitic lavas typically erupt from stratovolcanoes, they are not as abundant as andesite lava.
• Viscous dacitic-to-rhyolitic lavas generally ooze out of the volcano's central vent to form symmetrical lava domes

Characterisitics of Dacitic to Rhyolitic lava

• High viscosity
• High gas content

Volcanic Landforms

VOLCANIC LANDFORMS

Volcanic landscapes contain diverse landforms. The most recognizable of these include volcano edifices, calderas, and lava domes. Each of these landforms can vary markedly in size, shape, composition, and eruptive history.

DIFFERENT TYPES OF VOLCANOES:




We shall look into two types of volcanoes: Shield volcanoes and stratovolcanoes.

1) Shield volcanoes:

- Broad, low-profile features with basal diameters that vary from a few km to over 100 km
- Gentle lower slopes, steeper upper slopes
- Low viscosity of basalt lava leads to their broad shape


Three-dimensional image of the Alcedo shield volcano on Isabella Island, Galapagos

2) Stratovolcanoes:
- Also known as composite cones
- Gentle lower slopes, rise steeply towards the summit to produce an overall morphology that is concave in an upward direction.
- May contain several eruptive centres, caldera or amphitheatre as a result of a lateral blast.


Mt. Mayon

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