Science 7–10 · Year 8

See how they run: lava viscosity, temperature and added sand

Science understanding: Earth and space sciences (NSW Stage 4 focus area: Change)

PracticalLow risk

The idea

Hotter and less silica-rich lava is runnier, flows further and builds broad shield volcanoes; cooler, stickier lava builds steep cones and can trap gas until it explodes.

What you need

treacle or golden syrup, about 300 mL per group, and honey, three teaspoons per group
three identical clear plastic bottles with 50 mL of treacle each, immersed in water baths at about 5 degrees C (iced), room temperature and 45 degrees C (warm tap water) for 10 minutes
1 ceramic tile or smooth board propped on a wooden spacer to make a slope of about 20 degrees, 1 protractor
sand (half a teaspoon) and water (3 to 5 drops) to modify two of the honey samples; 1 stopwatch; 1 ruler

How to do it

Temperature: invert the three bottles at the same instant and time how long the treacle takes to reach the neck in each; record the bath temperatures.
Composition: place equal teaspoons of plain honey, honey with sand and honey with water along the top edge of the tile; predict, then tilt the tile and time each sample to the bottom edge (or measure how far each has run after 60 seconds).
Run each race twice and use the mean times.
Plot flow time against bath temperature and against the additive.
Match each sample to a volcano shape: which would build a shield like Kilauea and which a steep cone like Mount St Helens.

What you should see

The warm treacle reaches the neck first and the iced treacle last, clearly slower (the Earthlearningidea inverts three containers at three temperatures together; the higher the temperature, the lower the viscosity); on the tile the honey with water runs fastest and the honey with sand slowest, with plain honey between, the order the sheet states. The learner knows it worked when the two rankings, by temperature and by additive, both come out in the predicted order in both trials.

What changes

What you change: temperature of the fluid; additive (sand or water)
What you measure: time to flow a fixed distance
What you keep the same: fluid volume
slope angle
container or tile
start time

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

All lava is runny and fast; silica-rich lava barely flows and builds domes.
Explosive eruptions come from hotter lava; they come from stickier lava that traps gas.

Safety card

Low riskLearners carry it out

Hazards

warm water bath
slippery syrup on the floor

Controls

warm tap water only, below 50 degrees C
work over a tray and wipe spills

Note

No hazardous chemical and no flame or heating apparatus: a generic classroom risk assessment (CSIS 1.7 or RiskAssess) covers trips, spills, warm lamps and sharp edges.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7-10 Syllabus (2023), NSW Education Standards Authority (implemented from 2026; codes read at curriculum.nsw.edu.au on 22 and 23 September 2026)SC4-CHG-01 SC4-WS-03 SC4-WS-04 SC4-WS-05
Australian Curriculum v9AC9S8U03AC9S8U04AC9S8I02AC9S8I04

Sources

The pages the author read to write this activity.

All Concept Studio activities