Measurement Scales for Natural Events Measuring the size or strength of natural events has always been a challenge for natural scientists. They developed the Richter Magnitude scale to estimate the amount of energy released by an earthquake, the Saffir-Simpson scale to estimate a hurricane's potential, and the Fujita scale for rating the intensity of hurricanes. These scales are valuable for comparing different events and for understanding the amount of damage that events of different size can cause.

Measuring the strength of a volcanic eruption is more challenging than collecting wind speed data or measuring ground motion with an instrument. Volcanic eruptions produce different types of products, have different durations and develop in different ways. There is also a problem that some eruptions are explosive (rock materials are blasted from the vent), while other eruptions are effusive (molten rock flows from the vent).

Measuring Explosive Eruptions Chris Newhall of the United States Geological Survey and Stephen Self of the University of Hawaii developed the Volcanic Explosivity Index (VEI) in 1982. It is a relative scale that enables explosive volcanic eruptions to be compared with one another. It is very valuable because it can be used for both recent eruptions that scientists have witnessed and historic eruptions that happened thousands to millions of years ago.

The primary eruption characteristic used to determine the volcanic explosivity index is the volume of pyroclastic material ejected by the volcano. Pyroclastic material includes volcanic ash, tephra, pyroclastic flows, and other types of ejecta. The height of the eruption column and the duration of the eruption are also considered in assigning a VEI level to an eruption.

What’s the first thing that comes to mind when you think about getting old? Worsening health; a failing memory; not being quite as ‘quick’ as you once were? We have every reason to fear old age: along with its associated impact on our physical health, in the UK, one in twenty-five people between the ages of 70 and 79 currently live with some form of dementia, and of those people in their more senior years (80+ years old), one in six currently live with some form of dementia1.
While these statistics are shocking, it is at least somewhat comforting to know that, even in old age, the majority of us will not suffer this horrific syndrome. Even so, unless you’re Benjamin Button, unfortunately there’s no getting away from the fact that as you enter older age, you will have already started to suffer some degree of age-related cognitive decline. However, the severity of this decline is highly variable between individuals. What this means, of course, is that drawing any firm conclusions about the effects of ageing on our cognition is very difficult. Despite this, researchers continue in their efforts to better understand the consequences of the normal ageing process for cognition, focusing in particular on learning and memory.
So, what do we know about the consequences of the normal ageing process for learning? At a biological level, when it comes to age-related cognitive decline, the brain appears not to be equal2. It has been suggested, for example, that certain areas of the brain – such as the hippocampus and the dorsolateral prefrontal cortex (dlPFC) – are particularly vulnerable to the consequences of ageing, due to the fact that the cognitive functions they support (e.g. working memory) are often the first to show age-related decline. Moreover, certain types of synapse – structures within the nervous system that allow signals to pass from one neuron to another and, therefore, afford communication in the brain – have been shown to be more vulnerable than others. Finally, spine-like structures that protrude from the dendrites (arms) of a neuron also appear to be more or less susceptible to ageing depending on their type. These spine-like structures come in three main types – thin, mushroom and stubby (yes, they’re really called this!) – and recent findings from neuroscience have shown that the majority of age-related spine loss is of the thin type3.