Volcanic Landforms and Activity

Comprehensive practice flashcards covering the types of volcanic landforms, case studies of specific eruptions, and the causes and consequences of volcanic activity as described in the lecture notes.

What are the primary characteristics of acid or dome volcanoes?

They are steep-sided convex cones consisting of viscous lava (likely rhyolitic) with craggy, steep-sloped sides covered in rock debris, often found near large composite volcanoes.

How did the Novarupta Dome in Alaska form and what are its dimensions?

It formed during the 1912 eruption of Katmai Volcano and grew largely by expansion from within, measuring $800\,\text{feet}$ across and $200\,\text{feet}$ high.

What is the simplest type of volcano and how is it constructed?

Cinder cones are the simplest type, built from particles and blobs of congealed lava ejected from a single vent that solidify and fall as cinders to form a circular or oval cone.

What is the common sequence of formation for cinder cones as seen in the case of Paricutin?

The sequence typically involves the formation of the cone and crater first, followed by the quiet outpouring of molten rock as lava flows after excess gases have dissipated.

How is a lava plateau (or basalt flood) formed?

They are formed by large outpourings of basaltic lava from long fissures in the crust, which solidify and build up layer upon layer over time.

What are the dimensions and history of the Columbia Plateau basalt floods?

Occurring during late Miocene and early Pliocene times, lava flows covered approximately $63,000\,\text{square miles}$ over $10$ to $15\,\text{million years}$, reaching a thickness of more than $6,000\,\text{feet}$.

What defines a Strato or Composite volcano?

These are pyramid-shaped volcanoes tens of miles across and over $10,000\,\text{feet}$ high, consisting of alternating layers of solid lava flows mixed with volcanic ash or cinders.

Why are Strato volcanoes often characterized by explosive eruptions?

They erupt andesite lava which is cooler and more viscous than basalt ($70\%$ silica), allowing gas pressures to build up to high levels before exploding.

What is unique about shield volcanoes like Mauna Loa?

They are the largest volcanoes on Earth, featuring low slopes and consisting almost entirely of fluid basaltic lava ($45\%$ silica) that travels great distances.

How do Giant Calderas (Rhyolitic Caldera Complexes) differ from standard volcanoes?

They are the most explosive volcanoes and often lack a tall structure, instead forming huge collapsed depressions up to many tens of miles across; George Walker termed them "inverse volcanoes."

What occurred during the 1997 eruption of Soufriere Hills in Montserrat?

Periodic dome expansion led to pyroclastic flows and surges, including a major event on 25 June that covered $4\,\text{km}^2$ with $5\,\text{million cubic metres}$ of dome material, destroying houses and causing at least 9 confirmed deaths.

How is the volcanic risk managed at Popocatepetl in Mexico?

Through a hazard alert system based on three levels: green (low), yellow, and red (high), supported by real-time seismic monitoring, ground movement tracking, and emission chemistry observation.

Compare the chemistry and viscosity of Oceanic Rift vs. Continental Rift volcanism according to the lecture notes.

Oceanic Rifts produce basic lava ($45\%$ silica) with low viscosity; Continental Rifts produce acidic lava ($70\%$ silica) with high viscosity (approximately $100\times$ that of oceanic lava).

What are the size classifications for Tephra?

Tephra is classified as Bombs ($>64\,\text{mm}$ diameter), Lapilli ($2-6\,\text{mm}$ diameter), and Ash ($<2\,\text{mm}$ diameter).

What is an ignimbrite?

An ignimbrite is the resultant deposit from a pyroclastic flow that is high in pumice content.

Define a 'Lahar' and its cause.

A lahar is a volcanic mud-flow caused by rain or meltwater loosening tephra, which then moves downhill rapidly according to the topography.

What are three beneficial effects of volcanic activity mentioned in the text?

1. Tourism from scenic landscapes. 2. Fertile soils rich in potassium and phosphorus. 3. Industrial materials (sulphur, pumice) and Geothermal energy for heating and electricity.