Environmental Geochemistry of

LEADER: Chris Hendy, Associate Professor, University of Waikato, Hamilton,

START: Leaves from Rotorua on Friday 22 November, 2013

END: Finishes in Rotorua on Saturday 23 November, 2013

DURATION: Two days

SCOPE: This field trip will explore the unique aspects of lakes set in two modern rhyolitic volcanic centres. The environmental problems of eutrophication and sediment diagenesis, and the remediation strategies undertaken, will be demonstrated. Highlights of the trip, other than the spectacular scenery, will be examining the vast volumes of methane accumulated in the sediments of Rotorua and the huge pock marks created by its ebullition; and cruising over the recently rediscovered Pink Terraces in Lake Rotomahana.

DESCRIPTION: There are 14 lakes of volcanic origin in the Rotorua District. Some are craters, some calderas and the remainder dammed by pyroclastic flows. All are set in a landscape dominated by rhyolitic material ranging from rhyolite flows through ignimbrite to pumiceous sands, gravels and tephras. Several of the lakes have significant geothermal activity within them and many have geothermal springs within their catchments. Land use changes within the last century has greatly accelerated eutrophication in nearly all of the lakes to the point that large scale intervention is underway to attempt to halt the declining water quality.

The field trip will encompass cruises on three lakes: 1. : This is the oldest lake in New Zealand, probably in excess of 100 m of sediment (very low density diatomaceous ooze), supersaturated in methane and peppered with pockmarks 50 m in diameter and 5 m deep. We will fit a sub bottom sounder on the Lakeland Queen to display these as we cruise over them and Chris Hendy will take a core of the sediments. 2. 3. Lake Rotomahana: Geothermally active with silica precipitating onto the sediments, and the site of the destroyed in the Tarawera Eruption of 1886.

We will also visit several other lakes: 4. Lakes Rotoiti, where a diversion wall has recently been installed to reduce the flow of nutrient rich waters from Rotorua eutrophying Rotoiti. 5. , where draft tubes are being installed in 2012 to prevent anoxia in the bottom waters and limit the recycling of nutrients from the sediments 6. , the cleanest lake in the Rotorua District 7. Lake Okaro, formerly the most eutrophic lake in the Rotorua District, but where an extensive artificial wetland and reorganization of the dairy farm occupying the catchment (which we will visit) plus in-lake water treatment have dramatically improved the trophic status of the lake 8. Lake Rotowhero: a 19m deep hydrothermal explosion crater with boiling water entering from the bottom maintaining a constant temperature of 34°C and a pH of 3.4. This is an extremely productive lake with a single species of green algae supporting a vast population of insects and insect eating bird life.

Visits will also be made to: 9. Haumarana Springs: the largest springs in the resulting from solution cavernous weathering of the underlying ignimbrite and the single biggest source of phosphorus to Lake Rotorua 10. Okere Falls: another example of cavernous weathering in ignimbrite where a cave can be walked through that has clearly developed along intersecting joints 11. Tarawera Falls: spectacular cavernous weathering in rhyolite 12. Exiting from Lake Rotomahana will take us through the Waimungu Geothermal Park.

PROVISIONAL ITINERARY: To be notified

SPECIAL REQUIREMENTS: A moderate level of fitness is required. Sturdy footwear is essential and wet weather gear, sun hat and sunscreen are advised.

MAXIMUM NUMBER OF PARTICIPANTS: 20

MINIMUM NUMBER OF PARTICIPANTS: 8

COST: $370. Cost will include transport (by minivan, bus or coach), lake cruise fees, lunches, dinner and accommodation on Friday night and breakfast Saturday morning in Kawerau.

FURTHER INFORMATION: Email Chris Hendy at [email protected]

GALLERY

Lake Rotorua, with Rotorua city in the left foreground. Photo Lloyd Homer.

Lake Rotomahana (centre), with Waimangu thermal area in the foreground, MtTarawera in the distance and Mt Edgecumbe in the far distance. Photo Lloyd Homer.

Tarawera Falls