It is important to write with precision: qualify non-specific terms (‘large’, ‘extreme’) and back-up your arguments with examples:
Some scientists might oppose this conclusion because there were other large eruptions in 1991 – including the eruptions of Mount Unzen in Japan on 20th May and Mount Hudson in Chile on the 15th August – and the cumulative effect of these eruptions doesn’t seem so astounding. Moreover, the impact of the eruptions on global climate was only perceptible for three years, which is relatively short-term on a geological timescale. Consequently some would argue that the effect of sulphur dioxide on global climate isn’t particularly significant and that any minimal global cooling is countered by warming caused by the greenhouse effect.
The inclusion of two examples is good (although citations would have been helpful). However, the rest of the paragraph is too vague. Which scientists oppose the conclusion (cite their work) and who would argue that the effect of sulphur dioxide on global climate isn’t particularly significant? Who judges what is ‘astounding’? Express an opinion, but also provide the data so that the reader can decide. The following examples are similar:
During volcanic eruption events, vast quantities of volcanic gas, aerosol droplets and ash are ejected into the atmosphere.
The deep ocean represents what is agreed to be the most important overall record as sediment is allowed to build up undisturbed over very long periods of time
How big is ‘vast’? How long is a ‘very long period of time? One hundred years? One hundred million? The use of quantitative data is VERY important in physical geography essays. In the case of previous two extracts, it would be better to say something like:
Volcanic eruptions can release vast quantities of ash and gas into the atmosphere. For example, the 1991 eruption of Mt Pinatubo emitted more than 20 Mt of sulphur dioxide (Francis 1993).
The deep ocean represents what is agreed to be the most important overall record as sediment may accumulate for periods in excess of 2 million years (Lowe & Walker 1997)
Similarly, there is nothing inherently wrong with the following paragraph, but it could be so much more precise.
Spatial scales often relate closely to temporal scales. Temporal extent can be split into three categories; steady time, graded time, and cyclic time (Chorley et al, 1984). Steady time is used in relation to short time frames and generally encompasses small scale features such as a hill slope.
Generally, try to avoid qualitatively terms such as ‘short’, ‘large’ without giving the reader some idea of what you mean. For example, the preceding extract could read:
Spatial scales often relate closely to temporal scales. Temporal extent can be split into three categories; steady time, graded time, and cyclic time (Chorley et al, 1984). Steady time is used in relation to short (101 – 106 seconds) time frames and generally encompasses small scale (101 - 102 m) features such as a hill slope.
The following is a basic statement backed up with precise quantitative evidence and a citation: simple!
Firstly, the strength or resistance of surface materials of which hill slopes are composed determines denudation and therefore sediment yield rates. For example, concerning local rock types, sandstones in the Great Plains were shown to erode at 61mm/1000 year compared to the 853mm/1000 year of shale (Chorley et al, 1984).