Back-of-the-Envelope Calculations: Rate of Lava Flow
In 1983, an eruption began at Kilauea Volcano in Hawaii that has proved to be the largest and longest-lived eruption since records began in 1823. Lava has poured out of the volcano at an average rate of about 160 million m3 per year. To put those flow rates into perspective, let's suppose that the volcano was erupting directly into your classroom. At these flow rates, how long would it take to fill your classroom with lava?
About one minute! If your classroom is about 10 m x 10 m x 3 m (30' x 30' x 9'), your classroom would hold about 300 m3 of lava. 160 million m3 per year is about 5 m3 per second (there are 31,536,000 seconds in a year). If you filled your classroom with lava at the rate of 5 m3 per second, it would take only 60 seconds to fill your classroom! Imagine having a hose big enough to fill your classroom with water that fast!
References and Resources
This SERC page describes the use of Back of the Envelope Calculations
The Back of the Envelope : This page outlines one of the essays in the book "Programming Pearls" (ISBN 0-201-65788-0). The book is written for computer science faculty and students, but this portion speaks very well to back of the envelope calculations in general.